MXPA96003138A - Films and coatings that have anisotropic conductive lines in the mis - Google Patents

Abstract

An anisotropically conductive film or a substrate having a surface coated with a conductive anisotropic coating, the film or coating being formed by solidification of a composition comprising: (i) a solidifiable ferrofluid composition, the ferrofluid comprising a colloidal suspension of particles ferromagnetic in a non-magnetic carrier, and (ii) a plurality of electrically conductive particles dispersed in the ferrofluid, the electrically conductive particles having been ordered in a non-random pattern by application of a substantially uniform magnetic field to the composition, in a liquid, and having been secured in its position by solidifying the composition. The composition solidifies in a stage A, which usually involves a primary cure. In a final-use application of the particle or coating, the composition usually goes through a stage B or secondary cure. The coated film or substrate is an article of manufacture for bonding conductors in the electronic industry.

Description

FILMS AND COATINGS THAT HAVE ANISOTROPIC CONDUCTIVE LINES IN THEMSELVES Technical Field The present invention relates to films and coatings having anisotropic conductive lines thereon, and to methods for making the films and coatings, and to electronic components having such coating thereon. The present invention is particularly for use in interconnection technology in the electronics industry.

Previous Technique Electronic components such as semiconductor chips, circuit boards, flexible connectors and visual displays often have very small connectors such as bearings, spikes and conductors and have minimum intervals (separations) between connectors. Conventional welders can cause difficulties because the welder can fill the gap between two adjacent connectors on the same component. Therefore, anisotropically conductive adhesives have been proposed for electrical interconnection. An anisotropically conductive adhesive (ACA) conducts electricity only in one direction (usually designated as the Z direction) and must eliminate conduction in the plane perpendicular to it (X and Y directions). In Journal of Electronics Manufacturing (1992) 2, 109-118 of Ogunjimi et al. Reviewed several proposals for anisotropically conductive adhesives and are described in U.S. Patent Nos. 4740657 to Tsu Agoshi et al .; 3,359,145 to Salyer et al; 4,548,862 to Hartman; 4,644,101 to Jin et al; 4,170,677 to Hutcheson and 4,737,112 to Jin et al. In IEEF Trans. on Components, Hybrids and Manufacturing Technology, Vol. 16, (8), 1993, p. 972 (the content of which is incorporated herein by reference) Jin et al. Describe anisotropically conductive films consisting of a single layer of magnetically separated conductive spheres in a polymer matrix. In a vertical magnetic field, the ferromagnetic spheres in a viscous medium become parallel magnetic dipoles, and repel one another to produce a two-dimensional particle distribution which is described as uniform. This structure is then frozen by cooling or curing the polymer matrix, which may be an elastomer or an epoxy or thermoplastic adhesive. Anisotropically conductive adhesives that become anisotropic by the application of a magnetic field have not been adopted commercially, as far as the present Applicants know. The proposals of Jin et al. (Dating from 1986, as shown in United States Patent Number 4 737 112) require specialized particles that are both magnetic and electrically conductive. Magnetic particles that have been distributed by a magnetic field can form undesirable branched projections, which can only be avoided by balancing the magnetic force on the particles with surface tension of the polymer and gravity effects. These branched structures are undesirable for interconnection in the field of electronics, where the distribution of conductive lines is critical. Therefore the ordering of magnetic particles in a regular adhesive matrix imposes limitations with respect to the type of particle (ferromagnetic), the field strength and the properties of the matrix. Ferromagnetic conductive particles such as Fe, Ni, and Co tend to have high densities, low compressibility, are prone to settle out of the formulations and are either toxic or easily corroded. It is, therefore, undesirable to use them as interconnection particles.

In Journal of Electronics Manufacturing (1993) 3, 191-197 (the content of which is incorporated herein by reference), Hogerton discusses the state of 3M's adhesive interconnect technology, with particular emphasis on anisotropically conductive adhesive films. Hogerton indicates that a new film construction will avoid the inherent limitations of the random dispersion of conductive particles and provide the direct adhesive flip-chip bond of non-rejected integrated circuits. However, the new film construction is not described. In an area of unrelated technology, it is known to make a magnetic liquid or "ferrofluid" consisting of a colloidal suspension of tiny ferromagnetic particles in a non-magnetic carrier liquid. A typical ferrofluid may consist of magnetite particles (FeOH4) having a particle size in the range of 2 nanometers to 0.1 micrometers (and an average size of about 0.01 micrometers) in kerosene as carrier liquid with a surfactant to prevent agglomeration of the particles (see Skjeltorp "One- and Two-Dimensional Crystallization of Magnetic Holes" in Physical Review Letters, Volume 51, Number 25, December 19, 1983, 2306-2309, Skjeltrop AT and Helgesen, G. Phyisica A, 176, 37, 1991; Skjeltrop A.T. J. Appl. Physics 57 (1), 3285, 1985); and U.S. Patent No. 4,846,988 to Skjeltrop, the contents of which are incorporated herein by reference. U.S. Patent No. 5,075,034 to Wanthal discloses a two-component adhesive composition which can be cured by induction heating (ie, with an induced magnetic field) and which contains conductive carbon black together with particles of iron oxide. However, it is not suggested that the iron oxide particles may be of such a small particle size as to form a colloidal suspension. Therefore, this patent is not related to the field of ferrofluids or anisotropically conductive adhesives. EP 0 208 391 A2 Ferrofluidics Corporation describes an electrically conductive ferrofluid composition which contains carbon particles having diameters of about 5 to 30 nanometers. It is intended that the composition be used in a ferrofluid exclusion seal apparatus for sealing the bolts of the computer's disk drive. JP 3095 298 Nippon Seiko KK discloses a magnetic fluid composition containing fine ferromagnetic particles and fine particles of at least one metal, an alloy or an electrically conductive ceramic as a material that imparts electrical conductivity. The conductive particles have a diameter distributed in the range of a few nanometers to a few hundred nanometers, while in the case of anisotropic particles the length of the longest particles can be a few tens of nanometers. In another unrelated area of the technology, U.S. Patent No. 4,946,613 to Ishikawa discloses a photostable ferrofluid for use in detecting a magnetic defect or for displaying magnetically recorded patterns. The photostable ferrofluid comprises a carrier, a ferrofluid in which the ferromagnetic particles have an adsorbed surfactant (or the surfactant is dispersed in the carrier) and a photostable resin. The photostable resin can be the carrier. The ferrofluid is applied to a surface that will be analyzed and then subjected to a magnetic field. The applied ferrofluid will be attracted to the portion where the magnetic flux is filtered, that is, to cracks or defects in the surface, and will expand to form a pattern corresponding to the configuration of the defective portion. A beam of light is then used to firm or harden the photostable resin in order to fix the defect pattern formed in this way. Ishikawa did not consider the application of a magnetic field to create a chosen particle alignment. followed by the fixation of this alignment. In the International Patent Publication Number WO95 / 20820 (hereinafter referred to as "the parent application", the content of which is incorporated herein by reference) published after the priority date of this application, corresponding to the Mexican patent application No. 95478 we have described a composition comprising: (i) a ferrofluid comprising a colloidal suspension of ferromagnetic particles in a non-magnetic carrier liquid, and (ii) a plurality of electrically conductive particles having substantially uniform sizes and shapes, dispersed in the ferrofluid. Preferably the average particle size of the electrically conductive particles is at least 10 times (and more particularly 100 times, more preferably 500 times) that of the colloidal ferromagnetic particles. The non-magnetic carrier liquid may be curable or non-curable and may be selected from: (i) a curable liquid composition, (ü) a mixture of a curable liquid composition and a liquid carrier in which the ferromagnetic particles have been suspended , and (iii) a non-curable carrier liquid, but if the carrier liquid is non-curable and the curable liquid composition is not present, the electrically conductive particles have a latent adhesive property.

In the parent application we have also described a method for making an anisotropically conductive bond between two sets of conductors, comprising: (a) applying to a set of conductors a layer of an adhesive composition comprising a curable composition as described above; (b) placing a second set of conductors against the adhesive composition layer; (c) exposing the adhesive composition layer to a substantially uniform magnetic field, such that the interaction between the ferrofluid and the electrically conductive particles causes the electrically conductive particles to form a regular pattern of particles each in electrical contact with a particle adjacent and / or with a conductor in one or both sets by means of which conductive lines are provided from one set of conductors to the other set, each line comprising one or more of the electrically conductive particles, - and (d) Curing the composition to secure the pattern in position and to bond the conductors. The parent application also describes a method for making an anisotropically conductive bond between two conductor juices, comprising: (a) applying to a set of conductors a layer of a non-curable composition as described above, wherein the electrically conductive particles have a latent adhesive property; (b) placing a second set of conductors against the layer of the composition; (c) exposing the layer of the composition to a substantially uniform magnetic field, such that the interaction between the ferrofluid and the electrically conductive particles causes the electrically conductive particles to form a regular pattern of particles each in contact with an adjacent particle and / or with a driver of one or both games; and (d) activating the latent adhesive property of the particles whereby conductive lines are provided from one set of conductors to the other set, each line comprising one or more of the electrically conductive particles, and the conductors are bonded by the particles. In a preferred feature of the invention of the mother application, pressure is applied to push the respective sets of conductors towards each other before and / or during the healing step or the activation of the latent adhesive property.

Description of the Invention It may not always be convenient to install an element to create a magnetic field at the assembly site of two sets of conductors. It is therefore an object of the present invention to provide other ways of achieving the benefits of the invention of the mother application. It is another object of the present invention to provide films or coatings that overcome the limitations of random dispersion of conductive particles., as described in the Hogerton study cited above, and that does not have the disadvantages of the technology of Jin and collaborators, using magnetically separated conductive spheres. The present invention provides an anisotropically conductive film or a substrate having a surface coated with an anisotropically conductive coating, this film or coating being formed by solidification of a composition comprising: (i) a solidifying ferrofluid composition, comprising ferrofluid a colloidal suspension of ferromagnetic particles in a non-magnetic carrier, and (ii) a plurality of electrically conductive particles, dispersed in the ferrofluid, said electrically conductive particles having been arranged in a non-random pattern by the application of a substantially uniform magnetic field to the composition in a liquid state and having been secured in position by solidifying the composition. In addition, the present invention provides an anisotropically conductive solid film or coating comprising a composition containing colloidal ferromagnetic particles and a plurality of electrically conductive particles arranged in a non-random pattern. The present invention provides either a film as defined above, or a substrate having a surface coated with a coating as defined above, as a material or article of manufacture. The term "film or coating" as used herein means a film or coating that is formed in order to have at least one accessible larger surface. This surface can be applied against an electronic component to achieve an electrical interconnection. The accessible surface can be protected by a release sheet or cover sheet that can be removed. The film or coating may suitably be in the form of a sheet or in the form of a roll. The term "film or coating" does not cover a layer that is formed in situ between two conductors for joining together, as described in the parent application. The term "ferromagnetic" as used herein includes ferromagnetic materials such as ferrites. The non-magnetic carrier liquid may be suitably solidifiable or non-solidifiable. The term "solidifiable" as used herein, means that it is capable of existing as a solid at ambient temperatures, for example temperatures of less than 40 ° C, more usually 20-30 ° C.

The solidifiable compositions include curable compositions that are cured to the solid form by exposure to an energy source, for example, heat treatment, electromagnetic radiation, or otherwise, hardenable compositions, compositions that solidify as a result of the evaporation of a solvent, and thermoplastic compositions that can be softened with heat but that return to the solid form with cooling. The word "Solid" as used herein means stable in form and includes a gel or polymer network. Preferably the composition can be cured and this includes a primary cure system and / or a secondary cure system. The present invention also provides a method for forming an anisotropically conductive substrate film or coating comprising: (a) applying to a substrate, a layer of a composition comprising: (i) a solidifying ferrofluid composition, comprising ferrofluid a colloidal suspension of ferromagnetic particles in a non-magnetic carrier liquid, and (ii) a plurality of electrically conductive particles dispersed in the ferrofluid, (b) exposing the liquid composition to a magnetic field to order the electrically conductive particles in a non-magnetic pattern. random, and (c) concurrent with or subsequent to step (b), exposing the composition to solidification conditions for the composition, and (d) optionally removing the solid composition layer from the substrate to form a film. The non-magnetic carrier can be solid at room temperature but can be heated during application to the substrate and / or exposure to the magnetic field. In one embodiment, it could be that the film or coating was not required to have adhesive properties, if for example it is to be used between two sets of conductors, which will be temporarily assembled for testing purposes, but which will not be joined. . However, it is generally preferred that the composition contain a secondary / latent adhesive / curing system, the secondary / latent adhesive / curing system being able to be activated in the end-use application of the film or coating. The exercise of the present invention generally involves two stages, a stage A and a stage B. The stage A, or primary solidification has the function of ensuring the order of the electrically conductive particles in position and producing a film or coating which is capable of be handled, either when it is not sustained or at least when it is sustained. Stage A may suitably involve a primary cure, for example by photocuring, heat, or E. rays. Solvent evaporation, cooling (in particular from a melt), chemical reaction (eg, polymerization), phenomena of physical association, etc., are also acceptable means of effecting viscosity increases to an effectively solid stage A condition following ordering in an initial fluid state. Stage B that occurs during the end-use application of the film or coating, may utilize the thermoplastic properties of the film or coating of step A, but preferably involves a cure, for example, to a thermoset condition. When the solidification of stage A has been effected by a primary cure, the cure of stage B is a secondary cure that can be used by the same healing system or a different one from that of stage A.

In one embodiment of the present invention, the composition is applied to the substrate, and then exposed to the magnetic field. In another embodiment of the present invention, the composition is exposed to the magnetic field while the composition is being applied to the substrate. The composition can be applied continuously or gradually. In the same way the substrate can pass continuously or gradually by the device that is applying the magnetic field. In one embodiment the composition is applied to the substrate by stencil or screen printing using stencil or screen printing equipment having one or more magnets mounted appropriately therein. The substrate may be rigid or flexible. A release layer can form the substrate and / or can be applied to the composition layer on the face away from the substrate. The release layer may be rigid or flexible. The present invention includes a substrate, preferably an active or passive electronic component, having conductors on its surface or periphery and having a coating, as described above, applied to its conductors. In accordance with one aspect of the present invention, the coating can be applied to an electronic component, more particularly to a silicon disk, as the substrate. The base disc with metallized patterns delineated therein is coated with a composition as described above, particularly an epoxy coating that can be rendered dry to the touch. The electrically conductive particles are arranged in a regular pattern by exposure to a uniform magnetic field, and the coating is cured (primary cure). Alternatively, a film "patch", previously formed in accordance with the present invention, is applied to the disk. In any case, the composition contains a latent thermal hardener in such a way that it has latent adhesive properties. The resulting product, when subdivided into chips, can be used for a "flip chip" union. Preferably, the average particle size of the electrically conductive particles is at least 10 times that of the colloidal size ferromagnetic particles, more particularly at least 100 times, more preferably at least 500 times. More suitably, the electrically conductive particles have an average particle size (measured in the smallest dimension in the case of non-symmetric particles) of at least 2 micrometers, while the colloidal ferromagnetic particles have an average particle size no greater than 0.1. micrometers, more preferably in the order of 0.01 micrometers. The interconnecting bearings generally have a width in the range of 10 to 500 micrometers, particularly in the order of 100 micrometers. The spacing between the bearings is generally less than 150 micrometers, particularly in the order of 100 micrometers. However, it is intended to reduce the separation below 100 micrometers, even to below 10 micrometers or less. The present invention facilitates such reduction of spacing or separation. In the preferred embodiments, the electrically conductive particles are arranged in a regular pattern in a monolayer. Preferably the electrically conductive particles have substantially uniform sizes and shapes. Substantial uniformity is not affected by the presence of some particles smaller than average (which may not function as conductive particles in the film) or some particles larger than average (which could be compressed and / or otherwise be able to reduce their size under the conditions of production of the film or coating, for example, agglutinated particles that could melt or deform). The size distribution for agglutinated powder particles is defined in accordance with test methods from the Institute for Electronic Circuit Interconnection and Packing, Lincolnwood, II. 60646-1705, United States of America. For example, under its IPC-TM-650 test method, the following distributions are cited: TABLE 2B% of Sample in Weight - Nominal Size in micrometers None Less than 1% 90% Minimum 10% Highest Highest Highest Among Less than 1 Type 4 40 38 38-20 20 Type 5 30 25 25-15 15 Type 6 20 15 15-5 5 The term "solidifiable ferrofluid composition" as used herein includes: (1) a colloidal dispersion of ferromagnetic particles in a solidifiable liquid composition (ie, the solidifiable composition acts as the carrier of the ferrofluid), or (2) a mixing a solidifiable liquid composition and a colloidal dispersion of ferromagnetic particles in a liquid carrier. Preferably, in the methods described above the composition cures or otherwise solidifies while the magnetic field is applied, or shortly after being removed from the field. In a feature of the present invention, pressure can be applied to the composition layer before and / or during the primary cure or other solidification step. According to another preferred feature of the present invention, the thickness of the film or coating is substantially equal to, or slightly less than, the average diameter of the electrically conductive particles. During exposure to the magnetic field, the thickness of the composition layer could be adequately greater than the average diameter of the electrically conductive particles, preferably not more than twice that average diameter, such that each particle is surrounded by the liquid carrier and be free to move in the layer of the composition. After the particles have been sorted by the magnetic field, pressure can be applied to the layer of the composition to reduce the thickness, so that the electrically conductive particles lie in, or protrude slightly from both surfaces of the film or coating. Alternatively, if compression is omitted, the thickness of the composition layer can be reduced by shrinkage during step A, for example as a result of curing or drying. If the particles are spheres that can be compressed, the thickness of the film or coating can be reduced by compression to less than the average diameter of the electrically conductive particles, such that the particles are compressed to a non-circular transverse shape and are increased. the area of electrical contact on the surface of each particle. The compression of individual particles at different degrees of compression can also compensate for some variations in the particle size and in the plane of the substrates. Electrically conductive particles having a core of polymeric material coated with an electrically conductive metal will have a degree of compressibility dependent on the extent of crosslinking of the polymer. It was found that the gold-coated polystyrene spherical particles supplied by Sekisui Fine Chemical Co., Osaka, Japan under the name AU 212, (which were found to have an average diameter of 11.5 microns) compressed into the Z axis under a Pressure of 3.3 MPa have a Z-axis dimension of 10.5 micrometers, that is, a dimensional ratio (Z / X) of 0.79 corresponding to a contraction of 8.7 percent on the Z axis. In one embodiment, the magnetic field is applied normal to the composition layer (ie the Z direction) and electrically conductive particles form a regular array of particles in a monolayer or in columns, depending on the thickness of the layer. With a monolayer there is mainly a filling of a single particle in the Z direction between two sets of conductors (when the film or coating is used between two sets of conductors). The regular pattern improves the reliability of the electrical contact. In a second embodiment the magnetic field is applied in parallel to the layer of the composition (ie, the X direction) and the electrically conductive particles form parallel chains of particles, each in electrical contact with a particle or adjacent particles thereof. chain. The chains are formed so that they lie parallel to the longitudinal axis of two sets of peaks or conductive tracks. Here again, the only particle that fills in the Z direction between the two sets of conductors is achieved, but the particles are also in electrical contact with adjacent particles in the same chain, in such a way that the reliability is further improved. In a case where two separate sets of peaks or conductive tracks are located on the opposite edges of an integrated circuit or other component, the layer of the composition will normally be interrupted in a central area of the component such that no particle-conducting chain extends across the width of the component to connect the two sets of conductors in the same component (unless in a special case this is desired). In the case of a "quad" component that has conductive peaks on four edges, with two sets at right angles to the other two sets, the layer of the composition is applied, exposed to the magnetic field and cured or activated in two steps, of such that the chains of conductive particles are formed in the X direction and in the Y direction with the appropriate alignments and interruptions in the respective areas. With the modality using a magnetic field normal to the composition layer, no significant alignment occurs in the X direction or in the Y direction, so no interruption of the composition layer or any alignment step is needed. double. The colloidal ferromagnetic particles of the ferrofluid are preferably magnetite, but other ferromagnetic particles can also be used as described in U.S. Patent Number 4,946,613 to Ishikawa, the content of which is incorporated herein by reference. Exemplary ferromagnetic particles include: (i) ferromagnetic oxides such as manganese ferrites other than magnetite, cobalt ferrites, barium ferrites, composite metal ferrites (preferably selected from zinc, nickel and mixtures thereof), and mixtures of them; and (ii) ferromagnetic metals selected from iron, cobalt, rare earth metals and mixtures thereof. A ferrite is a ceramic iron oxide compound having ferromagnetic properties with a general formula MFe204 wherein M is generally a metal such as cobalt, nickel or zinc (Chambers Science and Technology Dictionary, WR Chambers Ltd. and Cambridge University Press, England , 1988). The phenomenon of ferromagnetism is observed in ferrites and similar materials. However, these are included within the definition of ferromagnetic particles in the parent application and in the present. The diameter of the ferromagnetic particle can be in the range of 2 nanometers to 0.1 micrometers, preferably with an average particle size of approximately 0.01 micrometers. The content of the ferromagnetic particle can suitably comprise from 1 to 30 volume percent of the curable ferrofluid adhesive composition. In the case where a monomer forms the carrier of the ferrofluid, the suspension of ferromagnetic particles in the monomer may suitably have a particle content of 2-10 volume percent. Generally, a surfactant will be required for the stable dispersion of the ferromagnetic particles in the carrier. The surfactants can be selected from unsaturated fatty acids and salts thereof, wherein the fatty acid or the salt has one or more polar groups such as COOH, S03H, PO3H and mixtures thereof, or other well-known surfactants in the technique such as silicone-type surfactants, fluorine-type surfactants and the like. Suitable surfactants include sodium oleate, or oleic acid, silane coupling agents such as those available under Trade Mark SH-6040 from Toray Silicone Co. Ltd., Saloosinate LH from Nikko Chem. Co. Ltd., Surfactant X C95-470 which contains fluorine from Toshiba Silicone Co. Ltd .. The primary surfactants form a coating adsorbed on the surface of the ferromagnetic particles. In some circumstances, a secondary surfactant may also be required to achieve satisfactory dispersion, particularly an anionic surfactant, for example, an acid form of a phosphate ester, particularly an aromatic phosphate ester type surfactant such as GAFAC RE610 of GAF ( Great Britain) Limited, Wythenshawe, Manchester, United Kingdom or RHODAFAC RE610 of Rhone-Poulenc Chimie, France. A suitable non-magnetic carrier liquid can be selected from those described in U.S. Patent Number 4,946,613 to Ishikawa, U.S. Patent No. 3843540 to Reimers or WO 95/20820 to those present. Applicants, the content of which is incorporated herein by reference. The carrier can suitably be an organic solvent selected from (a) hydrocarbons such as liquid fractions of intermediate boiling range such as kerosene and fuel oils, n-pentane, cyclohexane, petroleum ether, petroleum benzene, benzene, xylene , toluene and mixtures thereof; (b) halogenated hydrocarbons such as chlorobenzene, dichlorobenzene, bromobenzene and mixtures thereof; (c) alcohols such as methanol, ethanol, n-propanol, n-butanol, isobutanol, benzyl alcohol and mixtures thereof; (d) ethers such as diethyl ether, diisopropyl ether and mixtures thereof; (e) aldehydes such as furfural and mixtures thereof, - (f) ketones such as acetone, ethylmethyl ketone and mixtures thereof; (g) fatty acids such as acetic acid, acetic anhydride and mixtures thereof and derivatives thereof; and (h) phenols, as well as mixtures of the different solvents. Several authors have provided reviews on ferrofluids (Ferromagnetic Materials, Wohlfarth EP (Ed), Vol 2 Cap.8, p509- Charles SW and Popplewell J., North Holland Publishing Co. 1980, Aggregation Processes in Solution, Wyn-Jones E., Gormally, J. Cap. 18, p509, Martinet A Elsevier Sci. Publishing Co. 1983; Rosensweig RE Ann. Rev. Fluid Mech 19, 437-463, 1987). Commercially available ferrofluids such as those of Ferrofluidics Corp. NH, United States of America, comprise magnetizable particles dispersed in suitable carriers, the most common of which are water, esters, fluorocarbons, polyphenyl ethers and hydrocarbons. The typical properties of standard ferrofluids and other exemplary ferrofluidic characteristics are given in the parent application.

Ferrofluids are usually effective isolators. It is likely that the specific strength of a ferrofluid adhesive composition will increase after curing. The solidifiable composition is preferably an adhesive composition, and can be any suitable monomer composition within which the ferrofluid can be mixed or in which the colloidal magnetic particles can be dispersed. Numerous polymerizable systems based on acrylate, epoxide, siloxane, styryloxy, vinyl ether and other monomers, oligomers, prepolymers such as polyimides and resins and / or cyanate ester polymers and hybrids thereof can be used. Traditional anisotropically conductive adhesive films have been described, for example, by Emori and Tasaka in WO 93/01248 based on cyanate ester resins in conjunction with thermoplastic resin additives. The adhesive can be selected from olefinically unsaturated systems such as acrylates, methacrylates, styrene, maleate esters, fumarate esters, unsaturated polyester resins, alkyl resins, thiol-ene, and acrylate, methacrylate, or finished resins. in vinyl, including silicones and urethanes. Suitable acrylates and methacrylates are those which are used in polymerizable systems as described in U.S. Patent No. 4963220 to Bachmann et al. And U.S. Patent No. 4215209 to Ray-Chaudhuri et al. Also preferred are methyl methacrylate, polyfunctional methacrylates, silicone diacrylates and polyfunctional acrylated urethanes of the type known as useful in the formulation of adhesives (e.g., as described in U.S. Patent No. 4092376 of Douek et al.) Or a thiol-ene (for example, as described in U.S. Patent Nos. 3661744, 3898349, 4008341 or 4808638). Suitable epoxy systems are included among those described in "Chemistry and Technology of Epoxy Resins", ed. B. Ellis, Blackie Academic and Professional, 1993, London, Chapter 7 P.206ff. F. T. Shaw. Suitable styryloxy systems are as described in U.S. Patent Nos. 5543397, 5 084 490 and 5 141 970. The contents of all of the patents and texts mentioned above are incorporated herein by reference. In the case where the solidification process exploits the resolidification of a molten matrix material, suitable matrices include heat-melted polyamide adhesive polymers, Uni-Rez (R) 2642 and Uni-Rez (R) 2665, which are commercially available with the Union Camp Corporation in Savannah, Ga, and polyester polymers , Vitel (R) 1870 and Vitel (R) 3300, which are commercially available with the Shell Chemical Co in Arkon, Ohio. These materials have been described by Mathias in U.S. Patent Number 5,346,558 in traditional anisotropically conductive solder compositions and methods for using same. A condition that is applied to the adhesive system is either compatible with a commercially available ferrofluid, or capable of acting as a carrier for the magnetically treated, suitable magnetic particles, which are used in the preparation of a ferrofluid. The monomer composition can be curable by free radical, anaerobic, photoactivated, air activated, heat activated, moisture activated, instant, or other systems, such as the addition of hardeners to the resins. A curing system may be used in stage A or primary solidification, and a second curing system may be used in stage B. The monomer composition may comprise two polymerizable systems, one of which cures all or part of the stage A or primary solidification, and the second of which cures in stage B (accompanied by additional healing of the first system, if appropriate). A hybrid monomer, for example an epoxy acrylate, can be used.

The electrically conductive particles can be magnetic; although the magnetic field will be applied directly to such particles, the presence of the ferrofluid contributes to a pattern of aligned electrically conductive magnetic particles more structured than would be achieved if sp dispersed the particles in a composition without the ferrofluid. However, it is a preferred feature of the present invention that the electrically conductive particles are substantially non-magnetic. The term "non-magnetic" as used herein means that each particle has no significant net magnetic dipole. A particle with a non-magnetic core can have a coating of a metal (such as nickel), which is ferromagnetic in nature, but in view of the small coating volume, the net magnetic moment per unit volume of the particle is not significant. . The substantially non-magnetic particles do not respond to magnetic fields in environments that in themselves are not susceptible to magnetic fields, for example a non-ferromagnetic liquid medium. The electrically conductive particles can suitably have a size in the range of 1-300 micrometers. Spherical particles are preferred, but other spheroidal shapes, elongate shapes, cylindrical shapes, regular shapes such as cubic, or fibrous structures may also be used. For spherical particles, a diameter in the range of 2-100 micrometers, more particularly of 2-50 micrometers, especially of 5-30 micrometers, and more especially of 5-20 micrometers, is preferred, while for particles having a larger dimension and a smaller dimension, preferably the largest dimension is in the range of 2-300 micrometers and the smaller dimension is preferably in the range of 2-100 micrometers, particularly 2-50 micrometers, especially 5-30 micrometers, and more especially 5-20 microns, the dimensional proportion preferably being in the range of 15/1 to 1/1, more preferably 10/1 to 1/1. In the case of fibrous structures, a dimensional proportion of up to 50/1 may be acceptable, but fibers are the least preferred due to the danger of cross-contact, causing an incorrect interconnection between conductors, particularly in a thin layer of composition. Suitable particles could have a non-magnetic, non-conductive core, for example of plastic material such as polystyrene, or glass, coated with an electrically conductive metal such as nickel, silver or gold. A core of conductive material such as graphite or a metal can be used. Optionally the core can be hollow. Fiber particles or carbon solder can also be used.

U.S. Patent No. 5,346,558 to Mathias discloses welding powder whose particle size is less than 37 microns, and preferably less than 15 microns. WO 93/1248 by Emori et al. Describes a superfine welding powder, with an average diameter of 10 micrometers available with Nippon Atomizer. The electrically conductive particles form electrically conductive inclusions in the ferrofluid composition which is an insulator. The application of a magnetic field to the ferrofluid composition causes interactions between the colloidal magnetic particles and the non-magnetic conductive particles, such that they stabilize each other in a non-random structural pattern (chain conformation where the appropriate dimension of a layer of the composition so allows) due to the attractive interactions between particles and the repulsive interaction between chains. Indeed, there is a driving force to move the conductive elements relative to the insulating elements, so that the two systems are in mutually exclusive zones (see Skjeltorp, Physical Review Letters, Op.cit.). The concentration of electrically conductive particles in the composition is chosen in accordance with the desired spacing between those particles in the ordered array and other factors. With spherical particles of approximately 2 micrometers in diameter, a concentration in a monolayer of 107 particles per square centimeter may be adequate. A qualitative concentration in the range of 0.5-60 weight percent of the composition may also be suitable. See also U.S. Patent No. 5,366,140 to Koskenmaki et al., The content of which is incorporated herein by reference, particularly in column 2, lines 24-28, which cites average densities of approximately 600. 6,000,000 microgranules / cm2, more preferably 160,000 -6,000,000 granules / cm2. The optimal concentrations of conductive particles depends on many factors that those skilled in the art can determine through simple experimentation and / or mathematical calculations. Skjeltorp (Patent of the United States of North America Number 4.846988) indicates that the concentration of magnetic gaps in ferrofluids polarized with a magnetic field determines the distance between them. Shiozawa et al. (Lst International Conference on Adhesive Joining Technology in Electronics Manufacturing, Berlin, November 1994) indicates that contact resistance in traditional anisotropic conductive adhesives decreases as the particle count increases (per unit area). The larger the number of conductive particles, the greater the capacity to carry the current. The capabilities of carrying the current depend not only on the concentration but also depend on the type of particles (Lyons and Dahringer in "Handbook of Adhesives Technology, Pizzi and Mittal (eds), Marcel Dekker Ine 1994, p.578). , the actual concentration of conductive particles will depend on the type of particles, the density, the diameter, the electrical standard, the minimum contact resistance measurements required, the spacing between opposite and adjacent conductors, the surface area of the conductors, and so on. Li and Morris (lst International Conference on Adhesive Joining Technology in Electronics Manufacturing, Berlin, November 1994) have developed computer programs that calculate the minimum size of bearings for different load densities and the minimum bearing space for different particle sizes. of the conductive particles in conductive adhesives.The magnetic field can be applied by means of a permanent gneto or by electromagnetic elements. A preferred magnetic field is in the range of 10mT to 100mT, most preferably from 10mT to 100mT, applied for a time in the range of 0.1 to 10 minutes, most preferably 0.5 to 5 minutes. It is intended that the film or coating, in accordance with the present invention, be used in the electrical interconnection of active and / or passive electronic components, for example chip-on-board, chip-in-flex, chip-in-glass and Board / flex and flex / glass. The present invention is particularly suitable for the interconnection of driver sets with fine spacing and for "flip-chip" technology.

BRIEF DESCRIPTION OF THE DRAWINGS The embodiments of the present invention will now be described by way of example. Certain examples are supported with drawings. In the drawings: Figure 1 is an image analysis (20 optical fields, 100X magnification) of a light-cured ferrofluid film containing gold-coated polystyrene spheres of 11 micrometers in diameter (Example 1). The figure shows the field measure of percentage of area covered by the particles, against the field numbers. Figure 2 is a corresponding image analysis of the film of Figure 1 for the field density measurement of the particles in 1 / mm2 (X 1,000), against the field numbers. Figure 3 is a corresponding image analysis of the film of Figure 1 for the characterization of addition of the particles by measurement of area of the sample area (percent) against size. Figure 4 (a) is a diagram (side view) of an apparatus for carrying out the coating method of Example 2.

Figure 4 (b) is a top view diagram of the apparatus of Figure 4 (a). Figure 5 is an optical photomicrograph of the coating of amplified Example 2 X 100. Transmission Field: about 730 X 490 micrometers. The particles are approximately 10 micrometers in diameter. Figure 6 is an optical photomicrograph similar to Figure 5 of a coating prepared without exposure to a (comparative) magnetic field. Figure 7 is a magnetization curve as described in Example 3. Figure 8 is a viscosity-temperature profile as described in Example 3, the viscosity being measured in centipoise (Nm "2s x 103) Figure 9 (a) is a lateral elevation diagram of an apparatus designed and constructed to produce films having anisotropic conductive lines. elevation diagram of the apparatus of Figure 9 (a), taken on line AA in Figure 9 (a) Figure 10 shows an array of squares with sides of 100 micrometers and separated by 25 micrometers, superimposed on an optical photomicrograph of a fixed film without going through stage A containing 11.5 micrometer gold-coated polystyrene spheres (film prepared according to the method described in Example 5, using the formulation described in Example 7). A magnetic field before the photocure step In this figure the gray tones in the background have been reduced for clarity The arrangement of squares was generated by computer and overlaid in the micrologic afo on the computer. Figure 11 is an optical photomicrograph depicting the same sample as described in Figure 10, without the array of squares superimposed on the image. The gray tones have not been altered (cf Figure 10).

Ways to carry out the present invention EXAMPLE 1 Magnetite particles with an average particle diameter of 9.7 nanometers were coated (Liquids Research Limited, Unit 3, Mentech, Deiniol Road, Bangor, Gwynedd, UK) with oleic acid and dispersed in heptane at an appropriate content ( 3.5 percent and 8.4 percent) in magnetite volume to produce fluids with a magnetizable saturation of 100G and 250G as described below. Five milliliters of the aforementioned heptane-based material was added to 5 milliliters of butanediol dimethacrylate and an additional 2 milliliters of a secondary surfactant, which was an acid form of an aromatic phosphate ester sold under the Registered Trademark GAFAC RE610, was added. by GAF (Great Britain, Limited, and now available as RHODAFAC RE610 = GAFAC RE610 with Rhone Poulenc Chimie, France) This is described as nonoxynol-9-phosphate The result was a good quality ferrofluid with good stability. They prepared fluids with a magnetizable saturation of 100 G and 250 G. The saturation magnetization curve was exaggerated and typical of superparamagnetic systems in which it did not exhibit hysteresis.These fluids, even when formulated with radical initiators, were stable for periods of one year at room temperature, when they were stored in air-permeable polyethylene bottles such as those experts in the art use for the storage of traditional anaerobic adhesives. The butane diol dimethacrylate ferrofluids can be polymerized in the raw state with standard radical photo and / or thermal initiator systems. To the 100 g butanediol dimethacrylate based ferrofluid was added 10 weight percent / weight gold-crosslinked polystyrene spherical microparticles of 11 micrometer diameter and 6 weight percent / weight of the acetophenone photoinitiator of 2, 2- dimethoxy-2-phenyl.

Said particles are essentially monodisperse (i.e., substantially uniform in shape and diameter) and are an article of commerce of Sekisui Fine Chemical Co Ltd, Osaka, Japan. The photocurable, particle-loaded ferrofluid adhesive composition was applied to a rigid elongated substrate, and a flexible or rigid release layer was placed on top to form a three-layered structure. When the top layer was flexible, another rigid substrate was placed on top to ensure that it was flat and uniform pressure was applied across the multi-layer structure. The multi-layered structure was placed in the center of a Halbach magnetic cylinder (Magnetic Solutions Ltd, Dublin, Ireland). The cylinder had a central perforation of 28 millimeters and had a length of 63 millimeters and sent a uniform magnetic field of 0.26T which was normally applied to the substrate (multilayer). After approximately one minute, the multilayer was removed and photocoated for approximately 90 seconds with an Ultracure 100 SS ultraviolet ray lamp. The release layer was separated cleanly to leave a sustained coating, cured with uniformly aligned conductive particles secured in place. In this way the film section was achieved with a classification of high quality particles over areas larger than square centimeters. The ordering quality was evaluated with an Optical Image Analyzer (Buehler Omnimet 3 Image Analizer, Illinois, United States of America). Figure 1 illustrates the percent coverage of area over 20 optical fields, the standard deviation over 20 fields was 0.806 percent. The results in Figure 1 are summarized as follows: Minimum 14.993% Maximum 18.038% Medium 16.354% Standard Deviation 0.806% Field Area 100728.594 micrometers2 Total Area 2.015 e + 06 micrometers2 Field Count 20 Figure 2 illustrates the density of the particles distributed in the cured field over twenty randomly selected fields - the data indicate an average of approximately 5668 particles per square millimeter. The results in Figure 2 are summarized as follows: Minimum 5291,447 l / mm2 Maximum 6006,239 l / mm2 Medium 5667,706 l / mm2 Standard Deviation 240,559 l / mm2 Field Area 0.101 l / mm2 Total Area 2,015 mm2 Field Count 20 One was written computer routine to identify the incidence of the particle / particle interaction in the optical image in such a way that any visual 'objects' of size substantially larger than the diameter of 11 micrometers would be recorded and characterized as aggregates - the size of an aggregate being a multiple of this diameter of 11 micrometers plus a small margin for geometric error. In this way the size category of less than 13 micrometers can only capture individual particle objects (nominally 11 micrometers), the 13-26 micrometer category can only capture dimers, or two aggregates of particles (theoretically a maximum length of 22 micrometers end to end), and so on for an optical field comprising a layer of monolayer thickness filled with particles with respect to the diameter of the sphere. Figure 3 illustrates the data generated after the examination of twenty optical fields randomly selected for the ordered cured film. The results in Figure 3 are summarized as follows: 6.5 - 13 micrometers 14.281% 13 - 26 micrometers 0.067% 26 - 39 micrometers 0.015% 39 - 52 micrometers 0% 52 - 65 micrometers 0% 65 - 78 micrometers 0% 778 micrometers 0 % Total Area 2,015 e + 06 micrometers2 Field Count 20 It can be seen that 99.5 percent of the area analyzed was in the form of discrete individual particles, and the remaining 0.5 percent occurred only in dimeric form. The twenty optical fields analyzed were typical of the largest ordered regions of the macroscopic sample. Twenty fields amplified at 100X corresponded to a total area of approximately 2 square millimeters and consequently an average of 11336 particles of Figure 2. In this way, approximately 56 particles (0.5 percent) were non-discrete or individual particles in this experiment, but they were in fact in dimeric form, that is, only 28 particles were matched in the whole area. Pairing of particles to this extreme was probably due to inadequate wetting of these specific particles.

EXAMPLE 2 (a) In order to demonstrate the ordering in si tu of magnetic voids in a ferrofluid coating, the following experiment was conducted. A high-performance multi-purpose DEK 245 screen printer was modified in such a way that a substantially uniform magnetic field could be applied to a specific area of an overlay substrate, such that the direction of the magnetic field was orthogonal to the substrate and to the substrate. called 'work table' of the printer (DEK Printing Machines LTD, Dorset, England). As shown in Figure 4, the conventional work table of the DEK 245 was replaced with a custom-built work table, which included a polished aluminum surface plate (320 mm X 240 mm) (1) with a central milled depression (2) sufficient to accommodate a standard microscope glass slide (approximately 76 mm X 25 mm) (3). The polished plate was mounted on an arrangement of flat permanent magnets arranged in such a way that a magnetic material strip (4) of about 170 mm long and 50 mm wide lay directly below the milled depression in the plate, said depression being located approximately 70 mm from the draining end (5) of the belt, in such a way that a magnetic field was developed before the substrate (slide 3) with respect to the direction of printing, the direction of printing being that which moves the dripper paddle (5) from the left of Figure 4 (end A) to the right of the Figure (end B). The magnetic tape was constructed from a series of flat ferrite magnets each 40 mm X 25 mm X 8 mm (length X width X depth). These were polarized through their thickness and collectively sent a field strength of approximately 400 Oe, measured directly on the surface of the polished superimposed plate. Each magnet had its flat face parallel to the face of the top plate of the polished work table (1) and was arranged in such a way that the length dimension of each magnet was parallel to the length axis of the top plate. Flanking the central magnetic tape on either side, there were two similar tapes polarized in the opposite direction to the central tape. The three tapes were joined together to complete a magnetic circuit with vertical flow lines rising through the substrate coincident with the milled depression (2) in the top plate (1). In comparative experiments where no magnetic field was required, the same polished top plate was used, but the array of magnets below was temporarily removed. A ferrofluid formulation filled with particles was prepared based on a commercially available ferrofluid having a viscosity of 1500 cps (1.5 Nm "2s) (APG 057 available with Ferrofluids, Ine, NH, United States of America).

North America) and 10 weight percent of 11 micron transparent crosslinked polystyrene spheres (Sekisui Fine Chemical Co., Osaka, Japan). The spheres were completely dispersed in the formulation by vigorous mixing. The formulation was applied to the magnetic work table (1) on a 20 mm tape placed approximately 20 mm before the milled depression (2) which now contained a standard laboratory microscope slide (3). The work table was raised to a position that would allow the printing of a thin ferrofluid coating. The position of the work table, the printing speed, the printing pressure, and the type of drainer were adjusted in independent experiments to optimize the coating for the particular formulation under consideration. The motorized drip paddle pulled the formulation through the length of the microscope slide. During this coating action the filled fluid experienced a magnetic field. After the printing cycle, the free runner blade was lifted from the work table surface and returned to its original position ready for another operation. The coated substrate (3) was examined optically using a microscope connected to an optical image analyzer. The most modern equipment is capable of processing the image and evaluating the quality of field ordering of particles induced in the ferrofluid. The particles are arranged in the ferrofluid coating because they act as magnetic voids in the fluid matrix. Skjeltorp has described the phenomenon of magnetic voids (see for example "One and Two Dimensional Crystallization of Magnetic Holes" in Physical Review Letter, 51 (25), 2306, 1983) in fluid films that are confined in a cavity formed by two rigid substrates In this case, the coating was not confined. As illustrated in Figure 5, the image analysis of the coated substrate indicated that the result was a substantially uniform film with discrete particles dispersed therein. A comparative experiment was conducted using the aforementioned formulation and methodology with the exception that the magneto array was removed from the underside of the work table. In the Figure 6 the results of this experiment are indicated and clearly show that the particles are not uniformly dispersed or isolated as discrete particle entities. Although this Example was carried out using a non-curable ferrofluid composition and non-conductive particles, the Example illustrates the method that can be used in placing a coating in accordance with the present invention, as described elsewhere herein. (b) In order to show the effect with polymer-based systems, epoxy novolac ferrofluid solutions were developed. These essentially comprise resinous materials dissolved in volatile ferrofluids derived from methyl ethyl ketone (MEK) and toluene. Ferrofluid solvents were prepared having saturable magnetization values (Ms) of 112 and 166 G in MEK and toluene respectively. These were used to dissolve epoxy novolac DEN 438 EK85 (Dow Deutschland, Werk Rheinmuenster) and epoxy monomers of bisphenol F at an overall concentration of 20 weight percent / weight. The relative percentage weight of each constituent and curatives is listed below. The concentration, Ms, and viscosity of these solutions can be adjusted by solvent evaporation. Epoxy of Bisphenol F Dow, E.U.A. 78% DEN 438 EK85 (in ferrofluid solvent) 13.9% DICY (dicyandiamide) 7.0% BDMA (benzyldimethyl amine) 1.0% Conductive particles with a diameter of 25 micrometers to 10 weight percent / weight were loaded into the aforementioned drainage solutions and lowered onto conductive substrates such as copper or gold FR4 coated boards. The boards were put in place in an ACCU-LAB ™ downcoat (Industry-Tech., Oldsmar, Florida) and the formulation was lowered with a Meyer rod to give a wet thickness of apprately 40 microns. The coated substrate was placed inside a Halbach magnetic cylinder with the uniform 0.6 Tesla field placed normally to the plane of the sample. Polarization was performed when the film was still wet and evaporation of the solvent proceeded while the sample remained in the magnetic field until a viscous film was obtained. This was examined under the optical microscope and the ordering of particles was confirmed. Subsequently the film was dried by heating at 80 ° C for many hours (drying of step A). Copper substrates were placed on the dried films and joined by heating under pressure at 180 ° C for about 30 minutes (step B). Although the aforementioned formulations formed a film that was too brittle to be removed from the substrate even when coated for release, however the Example illustrates the method for securing particles in a polymer matrix which can be solidified by solvent evaporation (step A) and subsequently it is crosslinkable (step B).

EXAMPLE 3 A formulation based on epoxides was prepared based on the following composition: NAME COMMERCIAL COMPONENT / WEIGHT PROVIDER% Triglicidyl Ether Resin HELOXY 5048 38% Aliphatic (Shell Chemicals) Cycloaliphatic Epoxy Resin CYRACURE 10% UVR6351 (Union Carbide) Digicidyl Ether Polymer ARALDITE 6010 50% Bisphenol A (Ciba) Thermal and / or Photoinitiator 1 IRGACURE 261 2% * ( Ciba) Photoinitiator 2 GE1014 2% * (General Electric) In both cases the initiators were as 50 percent solutions in propylene carbonate. Therefore, the previous 2 percent refers to 1 percent real initiator (that is, a 50 percent solution).

A liquid film of said photo-cured composition in an 'A' stage (primary cure) after exposures of 2 X 60 seconds (one per side), yielded an adaptable solid film. This film could be transferred to a metal overlap and an adhesive bond formed by overlaying it with another metal overlap. When this 'sandwich' structure was clamped and heated at approximately 115 ° C for 30 minutes, the specimens of the metal overlap were strongly bonded (secondary cure). The composition described above was poured into a Ferrofluid by the addition of magnetite previously coated, using techniques known to those skilled in the Ferrofluidic art and mentioned in Example 1 of the application and also in the parent application. In Figure 7 the magnetization curve for the epoxy ferrofluid is shown. The magnetization saturation for this fluid was 97 Gauss. The viscosity-temperature profile for this fluid (designated) LOC 22 is illustrated in Figure 8. The viscosity of the Ferrofluid was further modified by dilution with 10 percent of the cycloaliphatic epoxy resin CYRACURE UVR6351. A thin liquid film of this composition can be photo-etched to form an adaptive film as previously noted. However, the ferrofluidized version had increased exposure times (2.5 minutes per side), even with increased levels of photoinitiators. To the liquid epoxy ferrofluid composition was added 15 percent (w / w) of 11.5 micron gold-coated polymer monospheres, available from SEKISUI KK, Osaka, Japan. Using this conductive composition charged with particles, a thin liquid film was prepared on two conductive substrates, i.e. ITO coated glass and copper plate. In both cases, a transparent polyester film was placed on top of the liquid film. Another rigid substrate was placed on top of the polyester and pressure was applied by hand to squeeze the liquid film into position before polarizing in a uniform magnetic field 0.6 Tesla in force (normally applied to the plane of the substrate). Polarization was conducted for a period of 1 to 5 minutes. The magnetic alignment times could be reduced by slightly heating the sample before sorting. There is a pronounced drop in viscosity in the ferrofluid composition as a function of temperature. (Figure 8). Following the magnetic ordering (polarization), the films were subsequently irradiated with ultraviolet rays to induce a stage A (primary) healing. After photo-curing, the backing polyester film was removed to expose the primary-cured, solid epoxy conductive coating loaded on a conductive substrate. Then another conductive substrate was clamped over the aligned conductive coating and the Z-axis contact resistance measurements were recorded using the four-point investigation method and a GEN-RAD 1689 DIGIBRIDGE PRECISION. Contact resistances were recorded that varied from 40 to 100 milliohms for the copper bound to the ITO (tin oxide of indium). The primary cured film, sandwiched between conductive substrates was subsequently subjected to a heat cure (110 ° C for 30 minutes) of stage B (secondary). The substrates were strongly bonded and the Z-axis contact resistance data were typically 50 milliohms for the copper bound to the ITO (tin oxide of indium).

EXAMPLE 4 As already described, adhesives derived from coatings or films can be made by subjecting stage B to a previously cast material. In such cases, the primary solidification, or stage A, may result from the evaporation of solvent and / or partially induced thermal curing. Stage A, which has the function of securing conductive particle arrays in place, can also be pre-formed by chemical reactions that cause partial gelling at temperatures that are, however, well below the thermal limit temperature required to trigger the latent polymerization catalysts that are used to activate the subsequent stages B, for example < 120 ° C in the case of dicyandiamide (DICY). An example of a system operating at room temperature involves the reaction between isocyanates and multifunctional polyols to produce a polyurethane. The ferrofluid content of such a formulation can be derived from a ferrofluid polyol, a ferrofluid isocyanate or from some other monomeric system which does not enter the polyurethane formation but which is present to provide a subsequent heat cure, by example, ferrofluid epoxide or acrylic monomers. The following formulation has been used to order conductive particles and secure them in place by chemical reactions (polyurethane formation) at room temperature, which were not aided by light: Hexamethylene Diisocyanate 1. lg Hydroxyethyl methacrylate (HEMA) 0.7g Ferrofluid-Butadiene di-glycidyl ether (MS = 343G) 1.47g DICY 0.07g Benzyl dimethylamine 0.015g polystyrene spheres coated with Au 0. lg of 25 micrometers Derivative systems were also prepared from versions of HEMA ferrofluid (Ms = 115 G, - viscosity at 27 ° C = 5.5 cPs 0.0055 Nm "2s.) However, the HEMA-based ferrofluid is unstable.An alternative proposal to ensure particles in ordered arrangements in ferrofluid adhesives involves photochemistry. it can be a cationic or photoinduced radical cure.The formulations that respond in this way can only be partially cured with light, or they can comprise two different types of reaction system that act independently (in the same or in different monomers). In previous cases, a cycloaliphatic and non-cycloaliphatic mixed system with photocatalytic initiators can be partially cured and subsequently thermally cured. in a stage B process. In the latter case, a blended acrylic-epoxy system could be designed and a photoinduced radical cure used to act on the acrylic functionalities to secure arranged conductor arrangements in place. The following examples describe these proposals in detail.

EXAMPLE 5 In order to produce high quality anisotropically conductive adhesives or films (anisotropically conductive adhesives or anisotropically conductive films (ACF) respectively) it was necessary to design specialized formulations and specialized equipment. Figure 9 illustrates the equipment for making the film and provides films up to about 20 square centimeters in area, although the test pieces routinely used were approximately 7.5 square centimeters in area. This Example describes in detail the apparatus that is used to produce films and the processing steps involved. As shown in Figure 9, carriage 10 which is a flat platform constructed from unpolished magnetic steel is used to hold the sample. The carriage comprises a vacuum nozzle to hold a substrate in place as well as a cartridge heater capable of raising the platform temperature to approximately 100 ° C, and a thermoelectric battery to detect the temperature. The car is mounted on a Tufnal base to avoid any thermal transfer to the substructure on which it rests. The car travels on a single track 11, also constructed from non-magnetic material. The arrangement is such that the assembled carriage assembly can be moved to specific positions from the left side of the appliance to the right. By doing so it can pass within the central plane of a large magnetic cylinder (Halbach) 17. When the processing is finished, the carriage can be retracted and moved from the right of the device to the left. The adhesive formulation of ferrofluid containing a plurality of conductors is applied to a coated substrate for release mounted on the top of the carriage 10. Said substrate is flat and can be reflective. A substrate treated in a similar manner is placed on top of the ferrofluid adhesive film. This substrate is a transmitter of ultraviolet rays. When the two substrates confine the ferrofluid adhesive composition comprising a plurality of conductors, the arrangement of the conductive particles is initially random in three dimensions. The confined fluid is placed and secured in its position in the next step of the film making process. If the initial assembly of the film is considered as step 1 of the process, the second step can be described as 'determination of wet film thickness'. In this second step, the assembled film is compressed by an apparatus identified by numbers 12-14 in Figure 9. The objective of this compression step is to produce a homogeneous fluid film by occupying the entire area of the upper confining substrate with liquid at excess being squeezed around the entire periphery of the upper substrate. The compression not only achieves a substantially uniform fluid film, but pressure is applied which produces a fluid layer between the substrates, such that the liquid layer is less than two conductor particle diameters in thickness. This situation is referred to as a monolayer of conductive particles. The fluid film is, however, thicker than a particle diameter so that the individual particles are free to move in the XY plane of the sample. The machinery used in this second stage comprises an air-driven cylinder 12 capable of sending a continuously variable pressure of up to 20 kilograms per square centimeter, a pressure measuring device 13 and a specially designed hub 14 that eventually applies pressure to the assembly. of film. The hub 14 is open on one of its vertical faces to allow optical access for an ultraviolet ray. In a position corresponding approximately to the diagonal of the hub, a high-quality mirror 15, placed to optimize the ultraviolet ray reflection, is mounted at an angle of 45 degrees or less to divert the light down towards the sample below. The lower face of the cube, that is, one that is parallel to the plane of the sample, is a high-quality fused silica flat cover 1 centimeter thick and approximately 5 centimeters on each side. This component is flat a? / 4 or better over 25 square millimeters measured in the laser line of the green Ar ion. The optical window at the base of the cube created by this component after assembly on the cube assembly is 3 centimeters X 3 centimeters. The flat optical cover sits remarkably from the base of the cube frame and consequently applies pressure through an area of up to 5 centimeters X 5 centimeters. The entire assembly attached to the cylinder 12 can be made to appear weightless by controlling differential pressure to the cylinder regulated through precision controls in the case 18. These controls also allow an extremely soft landing of the assembly on the sample below. The control box 18 also comprises heater control and feedback for the car cartridge heater. The remaining sides of the cube shell are polished metal optionally fitted with heat sinks on their outer surfaces. A heat sink can also be attached to the back of the mirror inside the bucket to remove any heat generated by the lamp. To generate a wet film having a thickness of about one conductive particle diameter, pressure controls are regulated to compress the film assembly. This requires pressures typically in the order of a few kilograms per square centimeter. The pressure is then removed and the film remains essentially at the compressed thickness. The carriage 10 carrying the compressed film is then inspected in step 3. The inspection is conducted with a reflective mode microscope 16 usually operating at a magnification of 200X. You can explore the length of the movie. The image is transmitted to a monitor by means of a video camera attached to the trinocular head of the microscope. When the operator is satisfied that the film is a monolayer with respect to the thickness, the assembly can be sent to the next step of the process. If the film is not a monolayer, it can be sent back one step and recompressed under different conditions until a satisfactory result is observed. Once in layer configuration, the film is advanced into the polarization gate 17 which comprises a large Halbach magnetic cylinder with a circular opening of approximately 55 millimeters and a length of approximately 140 millimeters. This permanent magnet has been designed and constructed to send a substantially uniform magnetic field over the vast majority of its length. The Halbach cylinder sends a field of 0.6 T, the orientation of which can be controlled by turning it in its cup-shaped housing. The strength of the magnetic field was selected to substantially saturate the ferrofluid compositions employed. In order to achieve a uniform dispersion of conductive particles, such as that illustrated in Figure 5, the normal field will be applied to the sample. However, it has been found useful to achieve very high degrees of order to first polarize the sample with the direction of the field parallel to the sample and then subsequently re-direct the field to a position normal to the sample. The period required for the polarization depends on different parameters, such as the composition of the fluid with respect to the magnetizable material, the magnetization saturation of the fluid in the specific field applied, the viscosity of the formulation, the temperature of the sample, and so on. The temperature of the sample can be regulated by heating the mounting platform 10. After the fourth polarization step, the sample is removed from the magnet and inspected again to verify the ordering of conductive particles. If the ordering is not satisfactory, the sample can be polarized again. In this fifth stage or in the third stage of inspection, the output of the video camera can be connected to an optical image analyzer which provides quality control of the ordering process. Then the fluid fluid film is passed again in step 6 to the compression position. The ordered sample can be photocured at this point with or without pressure applied to the liquid film. In this process, the sample is illuminated with ultraviolet light, number 19 in Figure 9, to induce photocuring and to secure the arranged conductors in their place. An Oriel one-kW XeHg arc lamp (LOT ORIEL, Leatherhead, Surrey, UK) with a beam diameter of 50 millimeters and fitted with a dichroic mirror and an electronic shutter was built into the film making device and is used to partially cure or pass through stage A to the anisotropically conductive films. After irradiation with ultraviolet rays, the pressure was released, if applied, from the assembly and the cured film was carefully freed from the substrates. The central section of the anisotropically conductive film thus produced, which was approximately 7.5 square centimeters in area, was used for the physical test. After cleaning or replacing the substrates, the operation can be repeated. The apparatus was designed to accommodate different types and sizes of conductive particles and formulations of different viscosity. In this way, the process parameters for the continuous film making equipment can be obtained.

EXAMPLE 6 In the present E.}. A typical formulation designed for the processing equipment mentioned above is described. The formulations should be designed in this way: a) to produce a film that passes through stage A, that is, a solidifiable form that can be handled in a sustained or non-sustained manner. The film that passed through stage A can be used in a thermoplastic system. b) to produce an additional curing step or step B, if a thermofixing is required, which is activated by the end user to cause adhesion between the substrates to be joined together. c) to be able to order "magnetic voids" in their fluid state, for example through the use of magnetizable fluids; this requires careful consideration of the viscosity of the fluid and / or its relationship to the temperature or resistance to shear stress, for example. d) to comprise conductors of regular geometry that provide conductive lines between the conductive bearings in one substrate and the tracks or conductive bearings in another. For the purposes of this Example and of the apparatus detailed in Example 5, step A was performed by photo-curing. However, the use of heat, curing with E-rays, evaporation of solvent, cooling, in particular from a melt, the chemical reaction, the phenomenon of physical association, etc. are also valid means to effect increases in viscosity at a condition that passes through effectively solid stage A, which is used to secure the arrangements in place after ordering in an initial fluid state. when using photo-curing it may be preferable to design a formulation such that the photo-curing mechanism is specific to certain components of the formulation and not effective towards others. Thus, for example, a combination of epoxy acrylate can be photo-cured by photolysis of a radical photoinitiator, such as benzophenone. In this case the functions of the acrylate are susceptible to healing while the epoxy functions are not. This scheme is preferable to an all-epoxy hybrid formulation comprising, for example, a mixture of cycloaliphatic epoxides and bisphenol A epoxies (cf. Example 3). In the latter case, cycloaliphatic epoxides are more susceptible to cationically induced light-curing than bisphenol A-type epoxies, so that a stage A can be carried out. However, because the hybrid formulation comprises only epoxides, it can not be make no clear distinction and undesirably cure, during stage A, a proportion of the bisphenol A type epoxides, intended to be subsequently cured in a stage B. If this happens, the last forces that can be achieved afterwards could be adversely affected from step B. In order to achieve extremely high degrees of ordering of conductors in the ferrofluid version of the adhesive formulations, it is preferred that the viscosity be less than 1500cPs (1.5Nm "2s), and more preferably less than of a few hundred cPs or less at the temperature of the polarization operation, it may also be preferable to ensure that the formulation initial n is any liquid in nature before addition of conductive particles. For example, liquid anhydride hardeners may be used to effect epoxy cure in stage B as alternatives to DICY. The preference for all liquid systems is related to the fact that any particle included in a ferrofluid formulation behaves like a "magnetic gap" once it is stimulated by a magnetic field. Thus, if conventional heterogeneous hardeners are used for epoxides such as dicyandiamide (DICY), they would behave as "magnetic voids". Although this is not a problem by itself, and you might even think it is convenient with regard to the distribution of curatives throughout the length of the adhesive, particles of this kind can be intertwined with the conductive array and consequently produce less than a substantially high ordered array of conductive particles. However, this becomes less of a problem if the DICY is of a small particle size, particularly if it is smaller in size than the conductive particles. A disadvantage of epoxies cured with anhydride is the speed of cure. However, those skilled in the art know that the catalysts substantially accelerate the cure with anhydride. Suitable catalysts can be liquids such as benzyldimethyl amine (BDMA) or semi-solids such as the HX epoxy hardening pastes from Asahi Chemical Industry Co. Ltd ..

An example of a catalysed formulation suitable for anisotropically conductive films is described below: Component Supplier Description Percentage p / p Resin Ebecryl ucb Chemicals Epoxide 16.8 604 Drogenbos, acrylated Belgium Methacrylate from Rohm & Haas, Acrylate 23.6 dihydrocyclopene- Germany tadieniloxyethyl Ether diglycid Alrich, Epoxide 15.8 butane E.U.A. diol (BDDGE) Bisphenol F Dow, E.U.A. Epoxide 15.8 Aldrich Nodic Anhydride, Hardener 21.5 E.U.A. latent Irgacure 1700 Ciba-Geigy, Fotoinicia3.0 United Kingdom dor HX3722 Asahi, Japan Catalyst 3.9 Such formulation is photocured after 20 seconds of irradiation by a medium pressure ultraviolet ray lamp at a film thickness of about 25 microns. A 36 mm2 Si die was placed on top of the light-cured film (which passed through stage A) and was bonded to a FR4 board with a force of 100 N and a heat treatment of 90 seconds at approximately 180 °. C. Average die shear strengths of about 450 N were recorded for this die size. A version of the above formulation was prepared by mixing ferrofluid adhesive monomers with standard monomers, as detailed below: Component Number Percentage Reference p / p FF Resin Ebecryl 604 7.3 FF - Dihydrodicide-methacrylate 3.0 clopentadienyloxyethyl 3 FF - Bisphenol F 14.8 4 Diglycidyl ether of Butanediol 15.0 (BDDGE) 5 Ebecryl resin 604 9.5 6 Dihydrodicyclo-19.5 pentadienyloxyethyl methacrylate 7 Anhydride NaDico 24.5 8 Irgacure 1700 3.0 9 HX3722 3.5 FF * refers to ferrofluid monomers prepared by Liquids Research Limited - see Example 1.

This can be done either by adding two monomers to a third one that has already been converted to a ferrofluid, or by using a monomer mixture as a single polymerizable carrier. In the first case, the production of a typical ferrofluid based on the low viscosity monomer of Dihydrodici-clopentadienyloxyethyl Methacrylate (Reference 2 above) is detailed below.

Heptane Intermediate: 404 grams of Ferric Nitrate are dissolved in pure water and filled to 500 milliliters. 150 grams of Ferrous Sulfate Heptahydrate are dissolved in water and filled to 500 milliliters. The above solutions are mixed together and 450 milliliters of ammonia solution is added (specific gravity: 0.88). 150 milliliters of oleic acid are added. The solution is acidified and the solid magnetite is separated. The solids are washed copiously with water and redispersed in heptane.

Production of ferrofluid of Dihydrodicyclopentadienyloxyethyl Methacrylate using a heptane material. The required amount of heptane fluid is precipitated and the solids are separated. 0.3 milliliters / 100 emu * of a phosphate ester surfactant such as GAFAC RE610, and 0.3 milliliters / 100 em of Bykanol-N dispersant are added from Byk-chemie GmbH, D-4230 Wesel, Germany. The required amount of monomer is added and heated to evaporate the residual solvent. * emu is "electromagnetic unit", which is an alternative unit for the expression of magnetic saturation. The density of the ferrofluid 4xPix converts emu / gram into Gauss units.

The percentages of approximate components resulting from the previous procedure are: Dihydrodicyclopentadienyloxyethyl Methacrylate = 80% Oleic acid = 5% Magnetite = 5% Bykanol-N = < 5% Phosphate Ester = 5% The above composition produces a ferrofluid of Dihydrodicyclopentadienyloxyethyl Methacrylate with a magnetization saturation of about 100 Gauss. Stronger fluids require an additional charge of magnetite. The final concentration of the fully formulated adhesive composition is determined by diluting high concentration monomeric ferrofluids that are relatively easy to prepare, with monomers that are not ferrofluid, more viscous. The three constituents of the formulation mentioned above, reference numbers 1-3, were derived from a single ferrofluid made from these components in the appropriate proportions. A colloidally stable mixture resulted in a viscosity at 27 ° C 1800 cPs (1.8Nm ~ 2s), and Ms 135 Gauss. The ferrofluid adhesive formulation indicated in the aforementioned table was cured and mechanically tested in the same manner as the non-ferrofluid version of the formulation. Average shear strengths of about 260 N were recorded. Additionally, when the formulation was loaded with 10 weight percent / weight of 25 micrometer polystyrene spheres coated with Au and aligned in a magnetic field, and then passed through stages A and B, in accordance with the present invention, the Z-axis contact resistance measurements, using the four-point research method, recorded 10 mOhms with an upper Cu substrate and a lower FR4 substrate coated with Au. To minimize the migration or exudation of a surfactant in the ferrofluid adhesive composition, it may be convenient to use a reactive or polymeric surfactant, such as is available from Monomer-Polymer Dajac Laboratories Inc., Trevose, PA 19047, E.U.A. (see also Wu, H.F. et al., Polymer Composites, 12 (4), 281, 199; Rao, A.V. and collaborators, Paint and Ink International, 15, 1995; Holmberg, K, Surface Coatings International, (12), 481, 1993).

EXAMPLE 7 In the present Example, the photochemistry was also used to effect the cure in step A, however the constituents of the formulation that respond to photocuring were derived from acrylic rather than epoxide monomers. The following is the basic formulation: Component Number Percentage Reference p / p Epoxide-Acrylate Resin 36.71 IRR282, ucb Chemicals, Drogenbos, Belgium 2 Bisphenol F, Dow, E.U.A. 10.84 3 Irgacure 1700, Ciba-Geigy, Kingdom 3.85 United 4 Butanediol diacrylate 26.92 5 DICY 5.24 6 Benzylated dimethylamine 0.35 7 Coated Spheres with Au, 16.08 Sekisui KK, Osaka, Japan In order to optimize the viscosity and magnetic strength of the formulation, the constituent 1 was derived from a ferrofluid based on IRR282 (Ms115 G, viscosity at 27 ° C of 115cPs = 0.115Nm "2s), and 29.86 by percent of the constituent 4 was derived from a ferrofluid based on butanediol diacrylate (Ms 116 G, viscosity at 27 ° C of 12 cPs = 0.012Nm "2s). The ferrofluids were prepared by Liquids Research Limited - see Examples 1 and 6. The residual balance of the constituent 4 was derived from a monomer of pure butanediol diacrylate. The formulation formed a stable colloid when all the ingredients were mixed. The magnetic strength of the resulting low viscosity formulation was approximately 50G. The gold-coated spheres had a diameter of either exclusively 12, or only 25 micrometers. Formulations of this type have been designed for a cure in stage A a manageable solid formula, which can be either sustained or non-sustained. In this case the films were unsupported or permanent free. The system that responds to photocuring is acrylic and reacts independently of the epoxy system, forming in this way a network of partially crosslinked polyacrylate surrounded by epoxy fractions, which are subsequently reacted in stage B. IRR282 resin, being an epoxy acrylate hybrid, serves to link the interpenetrating network of acrylic polymer and the epoxy polymer after heat activation. Alternatively, the acrylic film that forms the resins may not carry any hybrid epoxy function, such that the two systems remain completely independent after polymerization in the separate healing cycles. Formulations of the type described in this Example, which form a smooth film having epoxy monomers that can be fused, unreacted, interspersed throughout their structure, can be used to form anisotropically conductive films with a thickness of cured film in stage A larger than the diameter of a conductive filling particle, but less than two particle diameters. Due to the smoothness of the film that passed through stage A and the fact that the epoxy monomers can fuse and do not react at this stage, conductive bearings penetrate into the substrates that are to be joined, through the film until they make contact with the conductive filler particle, which lies slightly below the surface of the film that passed through stage A. This process is favored by the curing conditions of stage B, which requires the application of pressure at temperatures which are well above the melting temperatures of the epoxy monomers. This formulation was used in conjunction with the apparatus described in Example 5 to produce free permanent films comprising arrays of conductive particles, said films being capable of subsequent heat activation (step B) to produce an adhesive bond. When such films were used, comprising 25 micrometer spheres coated with gold, to join copper bolts to gold-coated FR4 boards, the Z-axis contact resistance measurements made using the four-point research methodology indicated resistance in the range of 16-22 mOhms. When the same formulation was prepared and films were produced comprising particles of identical diameter and core material, but without any conductive coating therein, the Z-axis contact resistance measurements indicated open electric circuits with estimated resistances being in the order of many hundreds of kOhms or MOhms. The silicone die was attached with an area of 36 mp ^ to uncoated FR4 boards, using the free permanent films and a force of 100N was applied for 90 seconds with a junction line temperature of approximately 180 ° C. The samples were allowed to stand at room temperature prior to the cut test using an Instron tension tester with a specially designed sample holder. The thrust forces of the 150 N die for the above formulation and the bonding conditions were typical. Figure 10 illustrates an array of squares with sides of 100 micrometers, separated by 25 micrometers in both directions X and Y, superimposed on top of a free permanent film that passed through stage A, prepared from the formulation of Example current. The square arrangement simulates an array of electrode bearings sized and placed similarly on a Silicon device, or the so-called 'flip chip' device. The magnetic gap nature of the particles causes a repulsive force when the system is polarized with a field normally oriented to the plane of the sample. This causes the non-magnetic particles to essentially repel each other and separate, which minimizes the potential for cross connections between electrode bearings superimposed or contacted with the film. The mottled gray texture of the Figure is due to the crystals of DICY (dicyandiamide) embedded in the film that passed through stage A. This can be discerned more clearly in Figure 11. DICY acts as a latent hardener catalyst that is used to initiate the curing reaction of stage B of the epoxy components of the formulation. The DICY crystals themselves will behave like magnetic holes, although irregular, and their separation by mutual repulsion, in the beginning, serves to help the uniformity of the healing through a more uniform dispersion of the healing. The DICY crystals thus dispersed do not interfere adversely with the distribution of the conductive magnetic egg spheres, as can be seen in Figure 10, in which the square-like bearings are separated by 25 micrometers in each of the X directions and X (parallel to the edges of the Figure). The DICY can be deployed in the formulation but removed from the interstitial spaces between conductive magnetic sphere spheres by means of firstly spherical showering with DICY in such a way that the latent hardener occupies the same position in the array formed as the conductive particle. Heating such a coating above the melting point causes it to induce cure in the epoxide and to flow from the conductive particle. Alternatively, liquid latent hardeners may be used to replace heterogeneous solid hardeners such as DICY. An example of a latent liquid hardener which does not interfere with the distribution of the conductive particles is nadic anhydride (Example 8). Figure 10 shows no incidence of cross connection between simulated bearings arising from chains or aggregates of particles. While the acrylic functions in the formulation serve to generate free permanent manageable films with latent adhesive properties, and the epoxy functions serve to polymerize during the operations of stage B, the double-functional IRR 282 material enters both types of reaction and serves to join together the epoxy and acrylic systems.

EXAMPLE 8 A formulation similar to that described in Example 7 was prepared, in accordance with the details that are expressed below: Component Number Percentage Reference p / p FF Epoxide-Acrylate Resin 26.8 IRR282, ucb Chemicals, Drogenbos, Belgium Bisphenol F, Dow, E.U.A. 12.5 Irgacure 1700, Ciba-Geigy, United Kingdom 4.5 Butanediol diacrylate 20.4 Anhydride Nádico, Aldrich, Kingdom 18.36 Kingdom 6 HX3722 2.5 7 Coated Spheres with Au, 15.0 Sekisui KK, Osaka, Japan FF * refers to ferrofluid monomer prepared by Liquids Research Limited - see Examples 1 and 6.

This formulation is based on the latent healing epoxide Naphthous Anhydride liquid. The formulation had a magnetic force of approximately 31G. The alignment of the conductive particles was facilitated by light heating before photocuring. Free permanent 25 micron films were produced after 20 seconds of ultraviolet irradiation. An Si punch of 36 mm2 area was attached in a step B operation on the light-cured film, which caused 90 seconds of heat treatment at 180 ° C and a force of 100 N applied to the die with the flip-bonding device. chip ('Fineplacer', FINETECH electronic, Berlin, Germany). Resistance to die average shear stress of 140 N was recorded. Electrical measurements on the Z axis show that the film had a resistance of 120 mOhms after submitting it to stage B.

Claims (20)

1. An anisotropically conductive film or a substrate having a surface coated with an anisotropically conductive coating, the film or coating being formed by solidification of a composition comprising: (i) a solidifiable ferrofluid composition, the ferrofluid comprising a colloidal suspension of ferromagnetic particles in a non-magnetic carrier, and (ii) a plurality of electrically conductive particles dispersed in the ferrofluid, these electrically conductive particles having been arranged in a non-random pattern by the application of a substantially uniform magnetic field to the composition, in a liquid state, and having been secured in its position by solidifying the composition.

2. A film or coating, according to claim 1, wherein the composition can be cured and comprises at least one primary curing system.

3. A film or coating, according to claim 1 or 2, wherein the composition contains a secondary / latent adhesive / curing system, whereby the secondary / latent adhesive / curing system can be activated in the end-use application. the film or coating.

4. A film or coating, according to any of claims 1 to 3, wherein the electrically conductive particles have substantially uniform sizes and shapes.

5. A film or coating, according to any of the preceding claims, whose thickness is substantially equal to the average diameter of the electrically conductive particles.

6. A method of forming an anisotropically conductive film or substrate coating comprising: (a) applying to a substrate, a layer of a composition comprising: (i) a ferrofluid composition that can be solidified, the ferrofluid comprising a colloidal suspension of ferromagnetic particles in a non-magnetic carrier liquid, and (ii) a plurality of electrically conductive particles dispersed in the ferrofluid, (b) exposing the liquid composition to a magnetic field to order the electrically conductive particles in a non-random pattern , and (c) concurrently with or subsequent to step (b), exposing the composition to solidification conditions for the composition, and (d) optionally removing the solid composition layer from the substrate to form a film. 7.- A method, in accordance with the claim 6, wherein the composition can be cured and comprises at least one primary cure system, and the solidification of the composition is achieved by means of a primary cure. 8.- A method, in accordance with the claim 7, wherein the composition contains a secondary / latent adhesive / curing system in addition to the primary curing system, the secondary / latent adhesive / curing system being activated in the end-use application of the film or coating. 9. A method, according to any of claims 6 to 8, which includes the application of pressure to the layer of the composition before and / or during curing or other solidification of the composition. 10. A method, according to any of claims 6 to 9, wherein the composition is applied to the substrate, and then exposed to the magnetic field. 11. A method, according to any of claims 6 to 9, wherein the composition is exposed to the magnetic field while the composition is being applied to the substrate. 12.- A method, in accordance with the claim 11, wherein the composition is applied to the substrate by means of stencil or screen printing, using stencil or screen printing equipment having one or more magnets mounted appropriately therein. 13. A method, according to any of claims 6 to 12, wherein the coating is applied to an active or passive electronic component, such as the substrate. 14. A method, according to any of claims 6 to 13, wherein the thickness of the layer of the composition exposed to the magnetic field is not more than twice the average diameter of the electrically conductive particles. 15. A method, according to any of claims 6 to 14, wherein the composition is heated during exposure to the magnetic field. 16. An anisotropically conductive film or substrate coating formed by a method according to any of claims 6 to 15. 1

7. An anisotropically conductive film in solid form or a substrate having a surface coated with an anisotropically conductive coating. solid form, comprising a composition containing colloidal ferromagnetic particles and a plurality of electrically conductive particles arranged in the composition in a non-random pattern. 1

8. A film or coating, according to claim 17, wherein the composition contains a secondary / latent adhesive / curing system that can be activated in the end-use application of the film or coating. 1

9. A substrate, preferably an active or passive electronic component, having conductors on its surface or periphery, and an anisotropically conductive film or coating, as defined in claim 1 or 17, applied to its conductors. 20. A substrate, according to claim 19, wherein the anisotropically conductive coating has latent adhesive / curing characteristics.