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WO1990008005A1 - Preparation d'articles au soudage - Google Patents

Preparation d'articles au soudage Download PDF

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Publication number
WO1990008005A1
WO1990008005A1 PCT/GB1990/000084 GB9000084W WO9008005A1 WO 1990008005 A1 WO1990008005 A1 WO 1990008005A1 GB 9000084 W GB9000084 W GB 9000084W WO 9008005 A1 WO9008005 A1 WO 9008005A1
Authority
WO
WIPO (PCT)
Prior art keywords
laser
radiation
metallic particles
pulses
soldering
Prior art date
Application number
PCT/GB1990/000084
Other languages
English (en)
Inventor
Norman Macleod
Original Assignee
Cookson Group Plc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Cookson Group Plc filed Critical Cookson Group Plc
Publication of WO1990008005A1 publication Critical patent/WO1990008005A1/fr

Links

Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/30—Assembling printed circuits with electric components, e.g. with resistor
    • H05K3/32—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits
    • H05K3/34—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits by soldering
    • H05K3/3489—Composition of fluxes; Methods of application thereof; Other methods of activating the contact surfaces
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K1/00—Soldering, e.g. brazing, or unsoldering
    • B23K1/20—Preliminary treatment of work or areas to be soldered, e.g. in respect of a galvanic coating
    • B23K1/206—Cleaning
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/10—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern
    • H05K3/12—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using thick film techniques, e.g. printing techniques to apply the conductive material or similar techniques for applying conductive paste or ink patterns
    • H05K3/1283—After-treatment of the printed patterns, e.g. sintering or curing methods
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/22—Secondary treatment of printed circuits
    • H05K3/24—Reinforcing the conductive pattern
    • H05K3/245—Reinforcing conductive patterns made by printing techniques or by other techniques for applying conductive pastes, inks or powders; Reinforcing other conductive patterns by such techniques
    • H05K3/246—Reinforcing conductive paste, ink or powder patterns by other methods, e.g. by plating
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00—Printed circuits
    • H05K1/02—Details
    • H05K1/09—Use of materials for the conductive, e.g. metallic pattern
    • H05K1/092—Dispersed materials, e.g. conductive pastes or inks
    • H05K1/095—Dispersed materials, e.g. conductive pastes or inks for polymer thick films, i.e. having a permanent organic polymeric binder
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
    • H05K2203/04—Soldering or other types of metallurgic bonding
    • H05K2203/044—Solder dip coating, i.e. coating printed conductors, e.g. pads by dipping in molten solder or by wave soldering
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
    • H05K2203/10—Using electric, magnetic and electromagnetic fields; Using laser light
    • H05K2203/107—Using laser light
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/0011—Working of insulating substrates or insulating layers
    • H05K3/0017—Etching of the substrate by chemical or physical means
    • H05K3/0026—Etching of the substrate by chemical or physical means by laser ablation
    • H05K3/0032—Etching of the substrate by chemical or physical means by laser ablation of organic insulating material
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/02—Apparatus or processes for manufacturing printed circuits in which the conductive material is applied to the surface of the insulating support and is thereafter removed from such areas of the surface which are not intended for current conducting or shielding
    • H05K3/027—Apparatus or processes for manufacturing printed circuits in which the conductive material is applied to the surface of the insulating support and is thereafter removed from such areas of the surface which are not intended for current conducting or shielding the conductive material being removed by irradiation, e.g. by photons, alpha or beta particles
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/30—Assembling printed circuits with electric components, e.g. with resistor
    • H05K3/32—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits
    • H05K3/34—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits by soldering
    • H05K3/3457—Solder materials or compositions; Methods of application thereof
    • H05K3/3468—Applying molten solder

Definitions

  • the invention relates to a method of preparing articles for soldering.
  • it relates to a method which is useful for improving the solderability of compositions comprising metal particles distributed within an organic polymer binder.
  • Thick film inks are printable pastes comprising a conductive filler distributed within a curable or fusible binder.
  • the conductive filler is generally in the form of powder or flakes of metal, for example silver or copper.
  • silver When silver is used it is sometimes alloyed with palladium to inhibit electromigration while copper may be coated with silver or a silver palladium alloy to improve the solderability of the resulting ink.
  • Nickel, gold aluminium, palladium and platinum/gold alloys have also been used.
  • the binders which are used fall into two classes; inorganic glasses and organic polymers. Silicate, phosphate or fluoride based glasses have been used. These bind by being fused at fairly high temperatures, for example in the range 600 to over 1000°C.
  • Organic binders have the advantage that they bind at lower temperatures than most glasses, for example up to 300°C. They include compounds which would react together to form a polymer binder and thermoplastic polymers which would fuse in an analogous manner to glasses or dry in a similar fashion to paints. Reactive cross-linking polymers which, once cured, will withstand elevated temperatures are preferred.
  • the most commonly used organic polymers are epoxies, polyesters, acrylics and silicones.
  • a method of preparing for soldering a surface of a composition comprising metallic particles distributed within an organic polymer binder characterised by including the step of irradiating at least part of the surface to be soldered with a controlled amount of ultraviolet electromagnetic radiation to ablate organic material from that surface and expose metallic particles.
  • metal particles is meant both particles consisting wholly of metal and particles which have a metallic coating on a non-metallic substrate.
  • Irradiation of the surface of such a composition with a controlled amount of ultraviolet electromagnetic radiation removes a surface layer of the organic polymer by ablation and thus exposes metallic particles comprised within the composition and previously covered by polymer binder. In this way the solderability of the composition is improved.
  • Most organic materials absorb strongly in the ultraviolet region and the energy absorbed at these wavelengths can break the bonds between the atoms. At higher wavelengths (lower energy) bond fission occurs less readily and may be further diminished by the fact that absorption rates are generally lower at higher wavelengths.
  • the strong absorption with ultraviolet means that when such light is shone on organic material absorption tends to occur in only a thin layer near the surface. Thus it is in that surface layer that bonds are broken and the material tends to decompose ablatively, that is, volatile molecular fragments break off from the surface.
  • the ablation conditions e.g. wavelength, energy density, can be adjusted so that there is little redeposition of molecular fragments and thus little contamination of the exposed surface or neighbouring surfaces.
  • compositions which have been ablated in this way exhibit improved solderability compared with unablated compositions. This is thought to be because more metallic material is exposed in the new surface than in the original surface.
  • the organic polymer binder in the composition may be any known binder such as epoxy, acrylic, polyester or silicone.
  • a preferred binder is epoxy resin.
  • the metallic particles distributed within the organic polymer may be, for example, silver, a silver/palladium alloy, palladium, nickel, aluminium, copper or a platinum/gold alloy. Preferably they comprise silver.
  • Solderability of polymer thick films generally improves as the amount of metallic particles present in the composition increases. However, to maintain adequate mechanical strength in the composite, the amount of metallic particles will be as low as possible while still maintaining the required conductivity.
  • the composition will comprise at least 20 vol% metallic particles (which is equivalent to at least about 70 wt% for particles consisting wholly of metal) but lower amounts may be used.
  • the ultraviolet radiation will preferably be produced by a laser. This is because lasers provide easily controllable amounts of radiation.
  • the radiation from lasers is usually highly monochromatic coherent and of high power. Laser light can be focussed to one particular area of a composition to be ablated and soldered without causing significant ablation of other nearby areas of the composition. However, in some cases where it is desired to irradiate a more general area a broad-area beam may be used. A mask may then be employed to cover areas which are to be protected from ablation.
  • excimer lasers which are generally used to provide pulsed radiation and such lasers are preferably used in the method of the present invention. These employ compounds known as excimers which have no stable ground state but that may have excited states when temporarily bound to other molecules. Examples are lasers which employ mixtures of noble gases with halogens. These include the following which provide outputs at the indicated wavelength.
  • F 2 gas may also be employed and this produces an output at 157 nm.
  • pulsed radiation of short duration such as that produced by excimer lasers in the process of the present invention to reduce the likelihood of heating the area beside and beneath the area being ablated. Heating is not desirable because it may cause deterioration of the heated article, e.g. printed circuit board, polymer circuit, or induce undesirable oxidation of the metallic filler.
  • the excimer beam may be focussed using quartz lenses or mirrors to produce a beam of the desired size, for example up to 2cm 2 . In this way a broad area can be ablated by a pulse of the beam without the need to scan the area as is the case for conventional collimated laser beams.
  • the angular distribution of the ablated material for e.g. 193 nm radiation directed at a polyimide film is generally within 25 - 30° of the surface normal for photochemical ablation.
  • etching occurs when the laser fluence (average energy density impinging on a unit area of the surface to be ablated expressed in mJ/cm 2 ) is above a certain threshold.
  • the threshold fluence varies with laser wavelength and the organic material. It ranges from e.g. 10 mJ/cm 2 for polymethyl methacrylate at 193 nm to 130 mJ/cm 2 for polyimide at 351 nm. Above the threshold fluence, each pulse ablates the same amount of material and the etch depth per pulse (If at wavelength ⁇ ) roughly obeys the relationship
  • a is the absorption coefficient of the polymer (cm -1 ) at the wavelength of the laser beam
  • F the laser fluence and F-t the threshold fluence.
  • the threshold fluence for three typical cured epoxy resins is given below for radiation of 193 nm and 248 nm.
  • compositions of the epoxies is given below.
  • Epoxy 1 Dow Chemical resin DER 351 cured with an acid anhydride (hexahydrophthalic anhydride) in an amount of 90 parts per hundred of resin.
  • Epoxy 2 Dow Chemical resin DER 351 cured with a modified polya ine (DP 500 from Anchor
  • Epoxy 3 Dow Chemical resin DER 351 cured with an imidazole (2E4MZ-CN from Anchor Chemicals) in an amount of 10 parts per hundred of resin.
  • ultraviolet radiation with an average energy density of 40 to 500 mJ/cm 2 at a wavelength of 193 nm and an average energy density of 100 to 500 mJ/cm 2 at a wavelength of 248 nm.
  • the radiation provided by an excimer laser will be in pulses having a fixed duration in the range 10 to 25 ns and a variable frequency. Particularly favourable results have been obtained at a frequency of about 1Hz. Higher frequencies up to about 200 Hz may be employed but as the frequency increases the likelihood of producing unwanted heating increases and so lower frequencies of the order of 0.5 to 10 Hz are preferred.
  • the surface to be ablated will be irradiated by 1 to 20 pulses, more preferably 5 to 10 pulses.
  • Ease of ablation may be improved by irradiating the surface with broad spectrum ultraviolet before employing the laser.
  • the surface is irradiated with an ultraviolet lamp prior to irradiation by a laser.
  • Compositions comprising metallic particles distributed within an organic polymer binder which have been irradiated in accordance with the present invention may be used in printed circuits which are to be soldered.
  • the present invention also includes a printed circuit prepared by the method of the invention and to which a component has subsequently been soldered.
  • the present invention also includes a method of soldering a surface of a composition comprising metallic particles distributed within an organic polymer binder comprising the steps of
  • Figures 1 to 4 are photographs showing the results of copper deposition tests on samples ablated under different conditions.
  • Figure 5 is a plot of current density against number of pulses for conductivity tests carried out on samples ablated under different conditions.
  • an excimer laser model
  • Questek 2460 which delivers a 2cm 2 pulsed beam with pulses of about 20 ns duration was used.
  • Example 1 A four inch square of FR4 epoxy fiber glass board was printed with silver loaded epoxy resin thick film ink of the composition given below using a screen printer to produce a test pattern of the thick film ink on the FR4 board. The epoxy resin was then cured for 1 hour at 180°C.
  • test pattern Certain parts of the test pattern were then subjected to ultraviolet irradiation from an argon fluoride excimer laser with an output at 193 nanometres to ablate the surface.
  • the laser beam was kept in a fixed position while the board was moved in front of it to enable irradiation of different parts of the board.
  • the irradiated parts of the board were each subjected to 20 pulses (1 Hertz) each pulse having an average energy density of 240mJ/cm 2 .
  • test pattern on the board was then tested for solderability using Alpha solder wire of 62 wt% tin, 36 wt% lead and 2 wt% silver with 2% by weight of the wire of a core of activated rosin flux as supplied by Alpha Metals Inc.
  • the areas of the test pattern which had been irradiated were easily solderable with the solder forming a strong bond with the polymer thick film.
  • Parts of the test pattern which had not been irradiated were also tested for solderability as a control. These areas were not solderable; the solder balled up, did not wet the substrate, and would not adhere.
  • composition of the thick film ink was:
  • a copper electroplating technique has been used to give an indication of the quantity of metal exposed by ablation of the surface of the polymer thick film so that the effect of different radiation conditions could be assessed.
  • Using a laser beam with a wavelength of 248 nm polymer thick films of an epoxy resin containing 78% by weight of silver were irradiated with different numbers of pulses at a rate of 1 Hz and at different energy densities.
  • the copper deposition tests were then carried out on the ablated areas at a current density of 10 mA/cm 2 during 90 s.
  • Two different polymer thick films were employed (PTF1 and PTF2) . The compositions of these are given below.
  • Epoxy resin (DER 351 from Dow Chemicals) 19.47 Curing agent (DMPF, Casamid from Thomas 0.97 Swan & Co. )
  • Curing agent (cishexahydrophthalic anhydride)
  • Photographs showing the results of the copper deposition tests are shown in Figures 1 to 4. All spot diameters are 3.5 mm (equivalent to the diameter of the f ⁇ cussed laser beam) except for the fluence 2000 mJ/cm 2 where the diameter is 2.0 mm. The number of pulses increase from left to right in accordance with the conditions quoted above.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Mechanical Engineering (AREA)
  • Laser Beam Processing (AREA)

Abstract

Un procédé de préparation au soudage d'une surface d'une composition comprenant des particules métalliques réparties dans un liant de polymère organique se caractérise par l'étape consistant à exposer au moins une partie de la surface à souder à une quantité commandée de rayonnement magnétique ultraviolet, de préférence fourni par un laser excimeur à implusions, afin d'éliminer de la matière organique de cette surface et d'exposer des particules métalliques.
PCT/GB1990/000084 1989-01-19 1990-01-19 Preparation d'articles au soudage WO1990008005A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8901114.2 1989-01-19
GB898901114A GB8901114D0 (en) 1989-01-19 1989-01-19 Preparing articles for soldering

Publications (1)

Publication Number Publication Date
WO1990008005A1 true WO1990008005A1 (fr) 1990-07-26

Family

ID=10650244

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1990/000084 WO1990008005A1 (fr) 1989-01-19 1990-01-19 Preparation d'articles au soudage

Country Status (3)

Country Link
AU (1) AU4947790A (fr)
GB (1) GB8901114D0 (fr)
WO (1) WO1990008005A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003037049A1 (fr) * 2001-10-22 2003-05-01 Invint Limited Formation de circuits par ablation laser de pate

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2000197A (en) * 1977-06-24 1979-01-04 Preh Gmbh W Method of producing a solderable conductive layer on a substrate
EP0140585A1 (fr) * 1983-09-30 1985-05-08 Electro Materials Corp. Of America Procédé pour la fabrication d'un film conducteur d'électricité soudable et composition conductrice d'électricité
EP0180101A2 (fr) * 1984-11-01 1986-05-07 International Business Machines Corporation Dépôt d'une configuration en utilisant l'ablation par laser

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2000197A (en) * 1977-06-24 1979-01-04 Preh Gmbh W Method of producing a solderable conductive layer on a substrate
EP0140585A1 (fr) * 1983-09-30 1985-05-08 Electro Materials Corp. Of America Procédé pour la fabrication d'un film conducteur d'électricité soudable et composition conductrice d'électricité
EP0180101A2 (fr) * 1984-11-01 1986-05-07 International Business Machines Corporation Dépôt d'une configuration en utilisant l'ablation par laser

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003037049A1 (fr) * 2001-10-22 2003-05-01 Invint Limited Formation de circuits par ablation laser de pate

Also Published As

Publication number Publication date
AU4947790A (en) 1990-08-13
GB8901114D0 (en) 1989-03-15

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