KR20070021159A - Etched Dielectric Film in Hard Disk Drive - Google Patents

Abstract

Etched dielectric film for use in hard disk drives. The dielectric film has a thickness of about 25 μm or more when attached to the supporting metal substrate, and is etched to a thickness of about 20 μm or less.

Etched Oilfield Films, Hard Disk Drives, Metal Substrates

Description

Etched dielectric film in hard disk drive {ETCHED DIELECTRIC FILM IN HARD DISK DRIVES}

The present invention relates to dielectric films useful in hard disk drives.

The etched copper or printed polymeric film on the polymeric film substrate may be referred to as a flexible circuit or flexible printed wiring. Originally designed to replace bulky wire bundles, flexible circuits are the only solution for the miniaturization and movement required in current cutting edge electronic assemblies. Ideal flexible circuit design solutions for thin, lightweight and complex devices range from single-sided conductive paths to complex multi-layer three-dimensional packages.

Flexible circuits are also used in hard disk drives. Modern computers require media that can store and retrieve digital data at high speed. The magnetization (hard) layer on the disk has proven to be a reliable medium for fast and accurate data storage and retrieval. Disk drives that read data from and write data to hard disks have become popular parts of computer systems. In order to access the memory location on the disc, the read / write head (also called "slider") is located slightly above the surface of the disc, while the disc essentially rotates below the read / write head at a constant speed. . By moving the read / write head radially over the rotating disk, all memory locations on the disk can be accessed. The read / write head is typically referred to as a " flying " head because it includes a slider that is aerodynamically arranged to float on a surface on an air bearing positioned between the disc and the slider that is formed when the disk is rotating at high speed. Lose. The air bearings hold the read / write head above the disk surface at a height called "flying height". The flexible circuit provides a connection to the magnetic head supported by the slider of the disc drive suspension assembly. This overcomes the difficulty of connecting the disk drive circuit to the small magnetoresistive (MR) write head.

Summary of the Invention

One aspect of the invention includes a flexure assembly of a hard disk drive comprising a metal substrate and a dielectric film attached to the metal substrate; The dielectric film comprises a polymer selected from the group consisting of polyimide, liquid crystal polymer and polycarbonate, wherein the dielectric film is etched to a thickness of less than about 20 μm from its original thickness of at least about 25 μm To provide.

Another aspect of the invention provides a metal substrate; Attaching a dielectric film to the metal substrate, wherein the dielectric film comprises a polymer selected from the group consisting of polyimide, liquid crystal polymer and polycarbonate, the film having a thickness of at least about 25 μm; A method is provided that includes etching the dielectric film to a thickness of less than about 20 μm.

Unless stated otherwise, the concentrations of the components are expressed herein in weight percent.

1 shows a flexure of a head gimbal assembly of a hard disk drive.

2A-2M illustrate steps involving the method of the present invention to fabricate the flexure structure of a hard disk drive.

Details of the invention are disclosed below as needed; However, it should be understood that the disclosed embodiments are merely exemplary. Accordingly, the specific structural and functional details disclosed herein should not be interpreted as limiting, but merely as a basis for the claims and as a typical basis taught to those skilled in the art for various uses of the invention.

Hard disk drive ( HDD ) And flexure

Starting materials for making integrated hard disk drive flexures typically include a support metal layer having a cast (ie, solvent-coated) dielectric layer or a thick dielectric layer bonded together by a metal support layer and an adhesive. . Casting films can provide a quick way to obtain thin films with certain desired thicknesses, but films of this type also have disadvantages. Cast films can be difficult to etch, which can make patterning of dielectric films difficult. In contrast, aspects of the present invention may select and use dielectric films (and adhesives, where applicable) that are easily etchable.

Flexible circuits typically use dielectric substrate materials with thicknesses greater than 25 μm. Automated handling and processing of films with thicknesses below 50 μm is known to be difficult and therefore not cost effective. Flexible circuits, such as flex-on-suspension circuits for hard disk drive devices, can provide improved device performance if the flexible dielectric substrate is thinner than 25 μm. As taught herein, the dielectric substrate may be uniformly etched to provide a thinner dielectric layer. In some implementations, it may be useful to further thin only selected regions or features of the substrate. For example, chemical etching for forming blind holes in a flexible circuit board may be advantageous because it can form an unsupported or cantilevered lead structure that cannot be manufactured by conventional physical methods.

The flexure of the head suspension assembly (HSA) represents a structural element of a hard disk drive that can be assembled using a multilayer composite. Flexures as described in US Pat. Nos. 5,701,218 and 5,956,212 include a layer of stainless steel for mechanical strength, a polyimide layer for electrical insulation, and a soft copper layer for electrical transfer.

The suspension flexure should be made using a very uniform material, which can be customized to have a small but very uniform characteristic. Since the degree of stiffness is critical to the performance of the flexure, the material thickness is very important. The requirement for increased data density requires floating the read / write head lower. Currently, typical heads of 60 to 90 GB / sq data capacity need to float below 10 nm on the rotating medium. This requires that the absolute stiffness of the flexure is reduced. Reducing the thickness of the dielectric layer and lowering the weight of the composite can result in flexure with improved flexibility.

The flexure base material is typically a stainless steel foil wound and quenched to at least 1/2 a hard state to create a fine and uniform particle structure. Preferably, it has a very uniform thickness in the range of 12 to 25 μm. The steel surface is typically etched to create fine regular textures of 0.1 to 0.5 μm RMS. Commonly used stainless steel materials are non-magnetic A.I.S.I. (American Iron and Steel Institute) A type 304 H-TA MW made by 302 or 304 grade steel, such as Nippon Steel (Tokyo, Japan).

Additional plating techniques or subtractives, starting with a composite laminate having a stainless steel layer for mechanical strength and a dielectric polymer layer for providing an electrically insulating carrier for conductive traces formed on the surface of the dielectric polymer film, The flexure may be produced by a subtractive treatment. Either method creates the circuit pattern needed to interconnect the magnetoresistive (MR) read-write heads to the hard disk drive.

1 shows a flexure 110 made in accordance with the present invention. The flexure 110 includes a flexible circuit interconnect 120 that supports the metal trace layer 122 and is coupled to the metal support structure 130. Gimbal arm 132 and tongue 134 are also part of metal support layer 130. Covercoat polymer 124 protects a portion of flexible circuit interconnect 120.

Etchant

High alkaline developer, also referred to as etchant, includes alkali metal salts and optionally solubilizers. Although a solution of alkali metal salts alone can be used as an etchant for polyimide, the etch rate is slow when etching LCP and polycarbonate. However, when the solubilizer is combined with an alkali metal salt etchant, it can be used to effectively etch polyimide copolymers with carboxyl ester units in the polymer backbone, LCP and polycarbonate.

Suitable water soluble salts for use in the present invention include, for example, potassium hydroxide (KOH), sodium hydroxide (NaOH), substituted ammonium hydroxides such as tetramethylammonium hydroxide and ammonium hydroxide or mixtures thereof. Useful alkaline etching agents include mixtures with aqueous solutions of alkali metal salts, especially alkali metal salts including potassium hydroxide and mixtures with amines, as described in US Pat. Nos. 6,611,046B1 and 6,403,211B1. Useful concentrations of etchant solutions vary depending on the type and thickness of the selected photoresist as well as the thickness of the polycarbonate film to be etched. Typically useful concentrations of suitable salts in one embodiment range from about 30% to 55% by weight, and in other embodiments range from about 40% to about 50% by weight. Typically useful concentrations of suitable solubilizers range from about 10% to about 35% by weight in one embodiment and from about 15% to about 30% by weight in another embodiment. Since KOH-containing etchant provides the best etched characteristics in the shortest time, the use of KOH with solubilizers is preferred to produce a high alkaline solution. The etching solution is generally at a temperature of about 50 ° C. (122 ° F.) to about 120 ° C. (248 ° F.), preferably about 70 ° C. (160 ° F.) to about 95 ° C. (200 ° F.).

Typically, the solubilizer in the etchant solution is an amine compound, preferably alkanolamine. The solubilizer for the etchant solution according to the invention can be selected from the group consisting of amines including ethylene diamine, propylene diamine, ethylamine, methylethylamine, and alkanolamines such as ethanolamine, diethanolamine, propanolamine and the like. It may be. The etchant solution comprising the amine solubilizer according to the invention works most efficiently within the above mentioned percentage ranges. This may indicate that there is a dual mechanism that acts to etch the polycarbonate or liquid crystal polymer, that is to say that the amine is most efficiently soluble for the polycarbonate or liquid crystal polymer within a limited range of alkali metal salt concentrations in an aqueous solution. It acts as a topic. By identifying the most effective range of etchant solutions, flexible printed circuits based on polycarbonate or liquid crystal polymers with microstructural features that could not be achieved using standard methods of drilling, drilling and laser ablation were previously available. It can manufacture.

Under etching conditions, the unshielded portion of the dielectric film substrate is melted by the action of a solubilizer, for example in the presence of a sufficiently concentrated aqueous solution of an alkali metal salt. The time required for etching depends on the type and thickness of the polycarbonate to be etched, the composition of the etching solution, the etching temperature, the spray pressure, and the desired depth of the etched area.

material

The present invention provides an etched dielectric film for use in hard disk drive flexible circuits. Etching the film to introduce regions of controlled thickness is most effective in films that do not swell in the presence of alkaline etching solutions. The dielectric film of the present invention may be a polycarbonate, liquid crystal polymer or polyimide, including a polyimide copolymer having a carboxyl ester unit in the polymer backbone. Preferably, the film to be etched is substantially sufficiently cured.

Current continuous roll-to-roll flexible circuit fabrication methods use basic dielectric substrates of 25 μm thickness. However, hard disk drive manufacturers are demanding thinner dielectric layers with thicknesses of 15 μm, 12.5 μm, and 10 μm or less for better flexibility. The thickness of the dielectric film substrate may be related to the degree of difficulty associated with manufacturing and manufacturing flexible circuits. If the film web is less than about 25 μm thick, material handling problems can make continuous fabrication of circuit structures difficult. Unsupported films of uniform thickness less than 25 μm tend to be irreversibly stretched or distorted during the multi-step process of printed circuit fabrication. This problem may be overcome by using the dielectric film according to the present invention, in which the film is thinned to less than 25 μm thickness after the film is attached to the metal substrate so that the metal substrate supports the thinned dielectric layer, which is a continuous roll It can be processed by a-to-roll flexible circuit manufacturing process.

Alternatively, the use of highly flexible dielectric film substrates with thinned areas includes suspension structures for hard disk drives. In hard disk drive applications, the flexible circuit can be made from a 25 μm film, but part of the flexible circuit in the head gimbal assembly advantageously has a size of 15 μm, 12.5 μm, 10 μm or less for better flexibility. It may have a thickness.

The presence of controlled depth etching of the dielectric material contributes to improving hard disk drive applications. For example, in hard disk drive applications, the main part of the flexible circuit may be made of a 25 μm dielectric film. The thickness reduction to about 12.5 μm provides a dielectric substrate with reduced stiffness in the head-gimbal assembly area of the circuit. This reduction in stiffness minimizes the impact of the dielectric film on the mechanical properties of the hard disk drive suspension. Reduction of the influence of the dielectric film results in less variation in the flying height of the read / write head. This increases the signal strength and can further increase the signal area density, which makes the memory capacity even larger. Thinning the film allows lower power motors to be used in power-sensitive portable hard drives.

Polyimide

Polyimide films are substrates commonly used for flexible circuits that meet the requirements of complex cut electronic assemblies. The film has excellent properties such as thermal stability and low dielectric constant.

As described in US Pat. No. 6,611,046 B1, it is possible to create chemically etched biases and through holes in flexible polyimide circuits, as is required for electrical interconnection between circuits and printed circuit boards. It is relatively common to completely remove the polyimide material for pore formation. When the polyimide film generally used is swelled beyond control in the presence of a conventional etchant solution, it is very difficult to control the etching without hole formation. Most commonly available polyimide films include monomers of pyromellitic dianhydride (PMDA) or oxydianiline (ODA) or biphenyl dianhydride (BPDA), or phenylene diamine (PPD). KAPTON H, K, E Films (available from E.I. DuPont de Nemuwa and Company, Circleville, Ohio, USA) and APICAL AV, NP Films (Otsu Kaneka Corporation, Japan) Polyimide polymers comprising one or more monomers may be used to make a film product. Films of this type swell in the presence of conventional chemical etchant. Swelling changes the thickness of the film and may cause local peeling of the resist. This may result in loss of control of the etched film thickness and may lead to irregular shaped features due to the etchant migration to the delaminated portion.

In contrast to other known polyimide films, there is evidence showing an adjustable thinning of the Apical HPNF film (available from Otsu Kaneka Corporation, Japan). The presence of carboxylic ester structural units in the polymer backbone of the non-swellable epical HPNF film indicates the difference between these polyimides and other polyimide polymers known to swell when contacted with an alkaline etchant.

 Apical HPNF polyimide films are believed to be copolymers that derive ester unit containing structures from the polymerization of monomers including p-phenylene bis (trimelitic acid monoester anhydride). Other ester unit containing polyimide polymers are not commonly known. However, it is reasonable for one skilled in the art to synthesize other ester unit containing polyimide polymers depending on the choice of monomers similar to those used for Apical HPNF. Such synthesis may extend the range of polyimide polymers for films that may be controllably etched, similarly to Apical HPNF. Materials that may be selected to increase the number of ester-containing polyimide polymers include 1,3-diphenol bis (anhydro- trimellitate), 1,4-diphenol bis (anhydro- trimellitate), ethylene Glycol Bis (Anhydro-Trimellitate), Biphenol Bis (Anhydro-Trimellitate), Oxy-Diphenol Bis (Anhydro-Trimellitate), Bis (4-hydroxyphenyl Sulfide) Bis (Anhydro -Trimelitate), bis (4-hydroxybenzophenone) bis (anhydro-trimelitate), bis (4-hydroxyphenyl sulfone) bis (anhydro-trimelitate), bis (hydroxyphenoxy Benzene), bis (anhydro- trimellitate), 1,3-diphenol bis (aminobenzoate), 1,4-diphenol bis (aminobenzoate), ethylene glycol bis (aminobenzoate), biphenol Bis (aminobenzoate), oxy-diphenol bis (aminobenzoate), bis (4-aminoben Joate) bis (aminobenzoate) and the like.

The polyimide film may be etched using solely potassium hydroxide or sodium hydroxide solutions, such as those described in US Pat. No. 6,611,046 B1, or by using alkaline etching agents containing solubilizers.

LCP

Liquid crystal polymer (LCP) films represent suitable materials as substrates for flexible circuits with improved high frequency performance, low dielectric loss and low water absorption compared to polyimide films. LCP films feature electrical insulation, less than 0.5% water absorption at saturation, a coefficient of thermal expansion that approaches the coefficient of thermal expansion of copper used for plated through-holes, and 3.5 over an operating frequency range of 1 kHz to 45 GHz. Dielectric constants that do not exceed. While the advantageous properties of liquid crystal polymers are known above, the difficulty in processing prevents the application of liquid crystal polymers to complex electronic assemblies. Etchants with solubilizers described herein allow the use of LCP films instead of polyimides as etchable substrates for flex-on-suspension assemblies. The similarity between the liquid crystal polymer and the Apical HPNF polyimide is the presence of carboxyl ester units in both types of polymer structures.

Non-swellable films of liquid crystal polymers include copolymers containing p-phenylene terephthalamide, such as BIAC films (Japan Gore-Tex Inc., Okayama, Japan), and LCP CT films (Kura, Okakayama, Japan). Aromatic polyesters, including copolymers containing p-hydroxybenzoic acid, such as Lay Company Limited).

Some embodiments of the present invention preferably use a laminated composite in which the dielectric layer is extruded and the liquid crystal polymer film is tentered (biaxially stretched). The process development described in US Pat. No. 4,975,312 is available under the trade names VECTRA (naphthalene based, available from Zest Celanese Corporation) and Zydar (biphenol based, available from Amoco Performance Products). A multiaxial (eg biaxial) oriented thermotropic polymer film of the identified, commonly available liquid crystal polymer (LCP) was provided. Multiaxially oriented LCP films of this type represent suitable substrates for flexible printed circuits, and circuit interconnects suitable for making device assemblies, such as flex-on-suspension assemblies used in hard disk drives.

The development of multiaxially oriented LCP films provides film substrates and related devices for flexible circuits, but limits the method of forming and bonding such flexible circuits. An important constraint is the lack of chemical etching methods for use with LCP. Without this technique, complex circuit structures such as unsupported cantilevered lead or through holes or biases with angled sidewalls cannot be included in the printed circuit design.

Polycarbonate

Polycarbonates have lower absorbency and lower dielectric losses compared to polyimides, which is a very important property for applications at high frequencies (GHz), for example for wireless communication or microwave devices.

Potassium hydroxide and sodium hydroxide solution alone may be used to etch the polycarbonate film, but the etch rate is too slow to effectively etch only the surface of the film. Etching capabilities to produce flexible printed circuits with thin polycarbonate substrates or polycarbonate substrates with voids and / or optionally formed recessed areas require specific materials and processing capabilities not previously disclosed. Shall be. To date, low-cost patterning of polycarbonate films has been a major problem preventing polycarbonate films from being applied in high volume applications. However, as disclosed and taught herein, polycarbonates can be easily etched when combining solubilizers with, for example, high alkaline aqueous etchant solutions including water soluble salts of alkali metals and ammonia.

Etching the film to introduce precisely shaped voids, recesses and other areas of controlled thickness requires the use of a film that does not swell in the presence of an alkaline etchant solution. Swelling may change the thickness of the film and cause local peeling of the resist. This results in loss of control of the etched film thickness due to etchant migration into the exfoliated site and can lead to irregular shaped features. According to the invention, the controlled etching of the film is most successful when using substantially non-swelling polymers. "Substantially non-swelling" refers to a film that swells by an insignificant amount when exposed to an alkaline etchant so as not to interfere with the thickness-reducing action of the etching process. For example, when exposed to some etchant solution, some polyimide will swell to such an extent that the reduction in thickness cannot be effectively controlled. Examples of suitable non-swelled polycarbonate materials include substituted and unsubstituted polycarbonates; Polycarbonate blends, such as polycarbonate / aliphatic polyester blends, including polycarbonate / aliphatic polyester blends, including those available under the trade name XYLEX from GE Plastics (Pittsfield, Mass., USA) (PC / PET) blend, polycarbonate / polybutylene terephthalate (PC / PBT) blend, and polycarbonate / poly (ethylene 2,6-naphthalate) ((PPC / PBT, PC / PEN) blend, and Other blends of polycarbonates and thermoplastics, and polycarbonate copolymers such as polycarbonate / polyethylene terephthalate (PC / PET) and polycarbonate / polyetherimide (PC / PEI) Another type of material suitable for use in the present invention is a polycarbonate laminate, which laminates at least two different polycars adjacent to each other. It may have a carbonate layer or may have at least one polycarbonate layer adjacent to a thermoplastic layer (eg, LEXAN, which is a polycarbonate / polyvinyl fluoride laminate from GE Plastics). GS125DL) The polycarbonate material may be filled with carbon black, silica, alumina, or the like, or may contain additives such as flame retardants, UV stabilizers, pigments and the like.

glue

The flexure for the trace suspension assembly (TSA) may use a laminate material comprising a metal layer, for example stainless steel foil (SST) bonded to a polyimide or polycarbonate polymer film by a bonding adhesive. The polymer film may be further bonded to another metal layer, for example copper (Cu) foil.

Suitable adhesives include thermoplastic adhesives such as thermoplastic polyimide (TPPI) or other wet chemical etchable adhesives. The adhesive is typically applied in a very thin layer, for example in the range of about 0.5 to about 5 μm thick. The adhesive-coated dielectric layer is typically heated both layers to a temperature within 20 ° C. of each other, but to a temperature of about 30 ° C. to 60 ° C. above the Tg of the adhesive material, followed by use of a heated counter platen or roll. They are pressed together and are typically laminated to stainless steel foil by forcing the adhesive into the surface tissue of the stainless steel. The desired adhesion measured at room temperature using the industry standard 180 ° peel adhesion test needs to be greater than 2 pounds / linear pli.

Non-adhesive

As an alternative to the laminates attached, a composite structure may be used to form the flexure for the hard disk drive. Thermoplastic films such as liquid crystal polymers and polycarbonates are suitable for forming composite structures without the use of adhesives. The thermoplastic film may be bonded to a supporting metal foil such as stainless steel by using an etching solution containing an alkali metal salt and a solubilizer to treat the surface of the film as an etchant. A metal foil having at least one acid treated surface will form bonds to the etchant treated surface when applying a pressure from about 100 psi to about 500 psi to the support metal foil and the thermoplastic film at a temperature flowing the thermoplastic film. . The bonding surface of the metal foil is typically treated with a strong acid etch composition. Suitable acid etchant for stainless steel include corrosive acids such as chromic acid and mixtures of nitric acid and hydrochloric acid.

The second side of the thermoplastic-metal laminate may be etchant treated to bond it to the second metal foil. International application WO 00/23987 describes the use of hot laminate presses to form laminate materials with molten liquid crystal polymer for bonding between stainless steel foil and copper foil. Such three-layer materials may be useful for flex-on-suspension (FOS) applications, trace suspension assemblies (TSAs), and related disk drive suspension assemblies.

Alternatively, the second side of the thermoplastic-metal laminate may be etched to form a surface suitable for metallization. Such metallization processes may include electroless deposition or vacuum deposition of seed layers that are reinforced with additional metal layers using conventional plating techniques. When using electroless metal plating, a method for producing a metal-seeded thermoplastic metal laminate comprises an aqueous solution comprising from about 30% to about 50% by weight potassium hydroxide and from about 10% to about 35% by weight s. Providing a thermoplastic-metal laminate substrate, which may be applied to provide a etched thermoplastic-metal laminate substrate. Applying the tin (II) solution to the etched thermoplastic-metal laminate substrate followed by the palladium (II) solution provides a metal-coated thermoplastic-metal laminate.

Improved bonding between the thermoplastic-metal laminate and support metal on one side and the metallized layer on the other side increases the integrity and durability of the composite structure. Metal-clad layers provide an alternative to forming printed circuits using additive processes, rather than the subtractive processes commonly used to form electrically conductive traces on carrier substrates.

Circuit-forming method

In addition to reducing the total thickness of the dielectric polymer film, the etchant disclosed herein can be used to form various features of the dielectric film.

Forming concave or thin areas, unsupported lead, through-holes and other circuit features of the film is typically used to protect portions of the polymer film using photo-crosslinked negative action masks, aqueous processable photoresists or metal masks. Needs one. During the etching process, the photoresist exhibits substantially no swelling or delamination from the dielectric film.

Negative photoresists suitable for use in the dielectric film according to the invention are described in US Pat. No. 3,469,982; 3,448,098; Negative functional and aqueous developable photopolymer compositions such as those disclosed in 3,867,153 and 3,526,504. Such photoresists comprise a polymer substrate comprising at least a crosslinkable monomer and a photoinitiator. Polymers typically used in photoresists include copolymers of methyl methacrylate, ethyl acrylate and acrylic acid, copolymers of styrene and male anhydride isobutyl esters, and the like. The crosslinkable monomer may be a polyacrylate, such as trimethylol propane triacrylate.

Aqueous commercially available aqueous bases, for example sodium carbonate developable negative functional photoresists used in accordance with the present invention, are commercially available from polymethyl-methacrylate photoresist materials such as E.I.Dupont de Nemu and Company. (RISTON) available, for example Liston 4720. Other useful examples include AP850 available from LeaRonal, Inc., Freeport, New York, USA, and PHOTEC HU 350 available from Hitachi Chemical Company Limited. A dry film photoresist composition under the trade name AQUA MER is available from MacDermid (Waterberry, Connecticut, USA). These are several series of accumulator photoresists, including the "SF" and "CF" series, and SF120, SF125 and CF2.0 are representative examples of such materials.

The dielectric film of the polymer-metal laminate may also be chemically etched in several steps in a flexible circuit manufacturing process. In order to thin the bulk film or only selected areas of the film while maintaining the bulk of the film at the original thickness, the introduction of an etching step may be used at the beginning of the manufacturing sequence. Alternatively, thinning selected portions of the film later in the flexible circuit manufacturing process may have the advantage of introducing other circuit features before changing the film thickness. Regardless of when selective substrate thinning occurs in this process, the film-handling characteristics remain similar to those associated with the manufacture of conventional flexible circuits.

2A-2M illustrate a method of making a fine pitch suspension assembly of the present invention. 2A shows a metal substrate 210, typically a stainless steel foil, on which a layer of dielectric material 212 is laminated thereon to form a laminate web structure. The dielectric may be laminated to the metal foil by using an adhesive or by melt-bonding the thermoplastic dielectric film. If an adhesive is used, a suitable adhesive may be an etched wet chemical such as TPPI, available under the tradename PIXEO from Token Kaneka, Japan. Stainless steel foils are typically 12 μm to 50 μm thick, in other embodiments 18 μm to 25 μm thick. The dielectric layer is typically about 25 μm to about 75 μm thick. The adhesive thickness is typically about 2 μm to about 5 μm.

As shown in FIG. 2B, the laminate web structure is passed through an etch bath that dissolves the dielectric film layer to form a thin dielectric layer 212 ′. The etching bath contains an etchant solution suitable for the type of dielectric layer applied to the metal foil as described above. The method can provide uniform etch depth in the transverse and longitudinal directions of the web. The laminate web is then placed in a sputter chamber, where a thin conductive layer is applied to the dielectric surface. The thickness of the sputtered layer is typically about 10 nm to about 200 nm. Typical materials used for this method include, but are not limited to, Ni, Cr and Ni / Co / Cu metal alloys (available under the trade name Monel from Special Metals Corporation, New Hatford, NY, USA) or sputtering. And other materials with a high melting point suitable for application by The web is then placed in a plating bath to form a conductive layer up to an overall thickness of about 1 μm to about 5 μm, which makes handling more difficult in subsequent processes (also, a low resistive magnetic field metal during subsequent electroplating steps). To act as Typical plating materials include copper and nickel. 2C shows a laminate web with a metal layer 214. A semi-additive process may also be used to circuit the laminate web. The surface layer may first be washed, for example, with a solution of potassium peroxymonosulfate such as E. DuPont de Nemu and Wilmington, Delaware, under the tradename SUREETCH. Next, a layer 218 of photoresist, which may be wet or dry, is applied to the metal substrate 210, and a layer 216 of photoresist is applied to the metal layer 214. The photoresist layer is then imaged and developed by exposure to appropriate radiation to form a circuit pattern as shown in FIG. 2D. The photoresist pattern limits subsequent metal electroplating to specific sites. Typically, the edges of the circuit pattern metal features are defined by the photoresist, thus making it possible to narrow the width, narrow the pitch, and make the features repeat. To provide a closer alignment between trace patterns that may occur on metal layer 214 and etched features in metal substrate 210, photoresist layers 216 and 218 may be simultaneously used using aligned phototools. You can also image. A subsequent step, such as shown in FIG. 2E, is to plate the metal in a circuit pattern on the metal layer 214 to form the circuit trace 220. During this process, the metal substrate 210 may be at a base potential or may be slightly opposite polarity relative to the potential of the metal in the plating bath to prevent the conductive trace metal from being plated onto the metal substrate 210 (alternatively Metal substrate 210 may be protected by a photoresist). As shown in FIG. 2F, another layer of photoresist 222 is applied to photoresist layer 216 and circuit trace 220. The photoresist is then flood exposed to form an insoluble blocking protection circuit trace 22. Subsequently, as shown in FIG. 2G, a portion of the metal layer 210 exposed by the pattern of the photoresist layer 218 is etched with a thin dielectric layer 121 ′. If the metal layer is stainless steel, suitable etchant may include iron chloride and copper chloride. As shown in FIG. 2H, the photoresist layer 222 and the remaining portions 216 and 218 of the photoresist layer are removed. Once the photoresist is removed, the underlying surface metal layer 214 and the thin layer 220 of circuit traces are etched away, leaving conductive circuit traces 220 as shown in FIG. 2I.

Subsequent steps include characterizing the thinned dielectric layer 212 ′. Initially, photoresist is applied to both sides of the existing structure. The phototool is aligned with the metal pattern on each side of the laminate structure, both layers of photoresist are imaged by exposure to appropriate radiation, and developed in the same manner as previously described. This results in patterned photoresist layers 224 and 226 aligned to circuit trace 220 and etched metal substrate 210, respectively, as shown in FIG. 2J. The exposed portions of dielectric layer 212 are then removed by shaping or by exposure, for example by exposure to plasma or chemical etchant, and the remaining portions of photoresist layers 224 and 226 removed. This leaves the flexure structure shown in FIG. 2K. Appropriate methods are known to those skilled in the art. Then, as shown in FIG. 21, another layer of photoresist, such that the circuit trace 220 can be plated with an additional layer of conductive material 228, such as gold, suitable for electrical bonding or contact compatibility. Alternatively, layers may be applied, imaged and developed on one or both sides of the structure. Optionally, as a final step, a layer of covercoat 230 may be applied, exposed and developed to form a protective layer over circuit trace 220 as shown in FIG. 2M.

An advantage of this method is that anywhere on the structure, features can be formed on both the metal substrate 210 and the metal layer 214. This makes it possible to create a "flying" (not supported by dielectric) of either an electrical trace or a structural (eg steel) element. Optionally, a dielectric material may be applied to the flexure structure that matches the functional requirements of the final product. The flexure is then ready to be stacked, attached or welded to the load rung of the suspension sub-assembly to form a complex head gimbal assembly for the hard disk drive.

A similar process is the fabrication of flexible circuits, including etching steps, which may be used with various known pre-etch and post-etch procedures. The order of these procedures may vary as desired for the particular application. A typical addition sequence of steps can be described as follows:

Using standard lamination techniques, an aqueous processable photoresist is deposited on both sides of a substrate, including a dielectric film with a thin copper side. Typically, the substrate has a polymer film layer of about 25 μm to about 75 μm and the copper layer is about 1 to about 5 μm thick.

The thickness of the photoresist is about 10 μm to about 50 μm. When both sides of the photoresist are exposed to the ultraviolet light through a mask in an image manner, the exposed portions of the photoresist become insoluble by crosslinking. The resist is then developed by removing the unexposed polymer with a dilute aqueous solution, for example 0.5-1.5% sodium carbonate solution, until the desired pattern is obtained on both sides of the laminate. The copper side of the laminate is further plated to the desired thickness. Subsequently, the polymer film is chemically etched by placing the laminate in a bath of etchant solution at a temperature of about 50 ° C. to about 120 ° C. as described above to etch away a portion of the polymer that is not covered by the crosslinked resist. . This exposes certain areas of the original thin copper layer. The resist is then stripped from both sides of the laminate in a 2-5% solution of alkali metal hydroxide at about 25 ° C. to about 80 ° C., preferably at about 25 ° C. to about 60 ° C. The exposed portions of the original thin copper layer are then etched using an etchant that is not harmful to the polymer film, such as PERMA ETCH, available from Electrochemicals, Inc.

In an alternative subtractive process, using standard lamination techniques, the aqueous processable photoresist is laminated again on both sides of the substrate with the polymer film side and the copper side. The substrate is comprised of a polymer film layer about 25 μm to about 75 μm thick, and the copper layer is about 5 μm to about 40 μm thick. The photoresist is exposed to ultraviolet light or the like on both sides through a suitable mask and the exposed portions of the resist are crosslinked. The image is then developed with dilute aqueous solution until the desired pattern is obtained on both sides of the laminate. The copper layer is etched to obtain a circuit, exposing a portion of the polymer layer. An additional layer of aqueous photoresist is deposited over the first resist on the copper side and crosslinked by flood exposure to the radiation source to protect the exposed polymer film surface (on the copper surface) from further etching. The area of the polymer film (on the film side) not covered by the crosslinked resist is etched with an etchant solution containing an alkali metal salt and a solubilizer at a temperature of about 70 ° C. to about 120 ° C. and the photoresist is Peel off from both sides with dilute basic solution as described previously.

Before or after etching through-holes and associated pores that completely remove the dielectric polymer material as needed to introduce conductive pathways through the circuit film, a controlled thickness of controlled thickness into the dielectric film of the flexible circuit may be used. It is possible to introduce areas. The introduction of standard voids into the printed circuit typically occurs halfway through the circuit fabrication process. By including one step for etching all the way through the substrate and the second etching step for etching the concave region of controlled depth, it is convenient to complete film etching within approximately the same time frame. This can be achieved by appropriate use of the photoresist and crosslinked in a selected pattern by exposure to ultraviolet light. Upon development, removing the photoresist reveals portions of the dielectric film that are to be etched to introduce the recessed areas.

Alternatively, concave areas may be introduced into the polymer film as an additional step after completing other features of the flexible circuit. An additional step requires stacking photoresist on both sides of the flexible circuit and then exposing the photoresist for crosslinking according to the selected pattern. Developing the photoresist using a dilute solution of the alkali metal carbonate described above exposes areas of the dielectric film that are etched to a controlled depth to create indentations and associated thin regions of the film. After sufficient time has passed to etch the recesses of the desired depth into the dielectric substrate of the flexible circuit, the protected crosslinked photoresist is stripped as before and the circuit containing the optionally thinned area is rinsed clean.

The method steps described above may be carried out in a batch process using individual steps or in an automated manner using an apparatus designed for delivering web material through the process sequence from the feed roll to the wind-up roll. This collects mass production circuits comprising controlled depth indentations and optionally thinned areas in the polymer film. The automated process uses a web handling device with various processing locations to apply, expose and develop photoresist coatings, as well as to etch and plate metal parts and to etch polymer films of starting metal onto polymer laminates. do. The etching location includes a plurality of spray rods with jet nozzles that spray etchant over the moving web to etch portions of the web that are not protected by the crosslinked photoresist.

Interconnecting tapes for flexible circuits, "TAB" (tape automated bonding) processes, such as gold, tin, or nickel, as required for reliable device interconnection, to make end products Conventional treatment may also be used to add several layers of copper and plating sites together in subsequent soldering procedures.

Example  1 to 4

material

Dielectric film substrate

A. BIAC Film-A 25 μm thick liquid crystal polymer (LCP) film made by Japan Gore-Tex Incorporated (Okayama, Japan).

B. Apical HPNF-Film (50 micron film) manufactured by Kaneka Corporation (Otsu, Japan).

Etchant  Furtherance

AA. 33 weight% potassium hydroxide + 19 weight% ethanolamine + 48 weight% deionized water

BB. 45 wt% potassium hydroxide + 55 wt% deionized water

CC. 35 wt% potassium hydroxide + 15 wt% ethanolamine + 50 wt% deionized water

Photoresist

Dry film photoresist was used for selected locations of areas for controlled etching. Photoresist materials are available from McDermid Incorporated (Waterberry, Connecticut, USA) under the trade names SF310, SF315 or SF320.

Table 1 shows a conventional automation for producing a 25 μm liquid crystal polymer film and a 50 μm polyimide film comprising a polymer derived from a p-phenylene bis (trimelitic acid monoester anhydride) monomer. Provide evidence that the device can be handled. During the flexible circuit fabrication process, the etchant shown in the table was automatically sprayed to controlly thin the area of the film exposed by selective removal of the photoresist. This creates a recess with a reduced film thickness of 25% to 50% of the original film thickness.

Polyimide and liquid crystal polymer Example 1 Example 2 Example 3 Example 4 film A B B B Etchant AA BB CC BB Temperature 71 ℃ 93 ℃ 82 ℃ 88 ℃ Line speed 38 cm / min 41 cm / min 102 cm / min 75 cm / min Thickness after etching 12.5㎛ 12.0㎛ 11.0㎛ 21.6 ㎛

The partial thinning method of the present invention can be very accurate. For example, Example 4 is a laminate of stainless steel and the 50 mm Apical HPNF film was etched with 45 wt% KOH etchant to reduce its overall thickness. The film experienced a residence time of about 1.5 minutes. The material obtained had an average thickness reduction to 21.63 μm with a standard deviation of 0.85 μm. The standard deviation of roughness of the original Apical HPNF film is 0.65 μm, indicating that the etching process is uniform across the web, both horizontally and vertically, with minimal effect on the surface roughness of the final laminate web.

Example  5 to 9 and Comparative example C1

For a series of examples, different etchant solutions were used to etch different types of polycarbonate films. An aqueous processable photoresist was laminated on both sides of the substrate with the polymer film side using standard lamination techniques. When imagewise exposing both sides of the photoresist through ultraviolet light through a mask, the exposed portions of the photoresist become insoluble by crosslinking. The resist is then developed by removing the unexposed polymer with a dilute aqueous solution, for example 0.5-1.5% sodium carbonate solution, until the desired pattern is obtained on both sides of the laminate.

For Examples 5, 7-9 and C1, the film was 2-sided etched. In other words, no coating or resist was applied to either side of the film, and as a result both sides were exposed to the etchant. To determine the etch rate determination, a small film sample (about 1 cm × about 1 cm) was cut and immersed in the etchant solution. As a result, a sample film etched on both sides was obtained. By dividing half of the reduced thickness by the etching time, the etching rate (on one side) was determined.

For Example 6, the film was etched one-sided. Dry aqueous processable photoresist was laminated on both sides of the polycarbonate film material. One side of the resist was flood-exposed and the other side was exposed under a patterned mask. The exposed portion of the photoresist became insoluble by crosslinking. The resist was developed by removing the exposed polymer with dilute aqueous 0.5-1.5% sodium carbonate solution, resulting in a polycarbonate film having a solid layer of resist on one side and a patterned layer of resist on the other side. . The rate for etching a single side of the sample is shown in Table 3. For single-sided etching, for example when covering one side with photoresist, the etching rate is half of the two sided etching rate. For polycarbonate films with resist, one side (2 mils thick) of the resist was first flood-exposed and the other side exposed under a mask and then developed. Unless specifically stated, using a water bath at 85 ° C., all etching experiments were carried out in a beaker without stirring. The etching results for the polycarbonate film are summarized in Table 3. Unless otherwise specified, the etchant composition is shown in Table 3 as the ratio of KOH to solubilizer (ethanolamine), with the remainder of the composition being water. For example, Example 5 shows '45 / 20 'in the etchant column, which indicates the etchant composition of 45 wt% KOH, 20 wt% ethanolamine and the remaining water. The names "A" through "I" correspond to polycarbonate films named A through I in Table 2 below.

Polycarbonate film Substance brand name Chemical composition Film thickness Where to get A1 LEXAN T2F DD112 Polycarbonate (smooth / matte finish) 132㎛ GE Plastics (Pittsfield, Massachusetts, USA) A2 LEXAN T2F DD112 Polycarbonate (smooth / matte finish) 260 ㎛ GE Plastics B LEXAN T2F OQ112 Polycarbonate (Optical Transparent) 254㎛ GE Plastics C LEXAN FR83 116 Polycarbonate with flame retardant 128 μm GE Plastics D XYLEX D7010MC PC and Aliphatic Polyester Blends 125 μm GE Plastics E XYLEX D5010MC PC and Aliphatic Polyester Blends 165 ㎛ GE Plastics F XYLEC D56 PC and Aliphatic Polyester Blends 164㎛ GE Plastics G LEXAN 8B25 Polycarbonate (filled with carbon black) 265 ㎛ GE Plastics H ZELUX Natural Film Polycarbonate (smooth / matte finish) 50 μm Westlake Plastics Company (Lenny, PA) I Macropole DPF 5014 Polycarbonate (Velvet, Very Fine Matte) 150 μm Bayer Plastics Division (Pittsburgh, PA)

Summary of Polycarbonate (PC) Etching Results Polyimide film type A1 A2 B C D E F G H I Example Etchant Single-sided Etch Rate (μm / min) 5 45/20 23.0 - 20 15.3 11.0 2.0 1.2 - - - 6 42/21 ^{* †} - 26.0 - - - - - - 14.7 19 7 40/20 15.6 - 14.1 9.0 7.1 1.3 1.2 17.0 - 11.9 8 36/28 15.0 - 14.8 10.0 7.9 1.6 1.5 - - - 9 33/33 11.5 - 11.1 7.6 5.0 1.8 1.7 - - - C1 45/0 2.5 - 2.8 1.2 1.0 0.2 0.034 - - - * The etching temperature was about 92 degreeC. † Titer results showed actual concentrations of 41.8 wt.% KOH and 20.9 wt.% Ethanolamine.

It will be appreciated by those skilled in the art, in light of the present disclosure, that various changes may be made in the embodiments disclosed herein without departing from the spirit and scope of the invention.

Claims (17)

A metal substrate and a dielectric film attached to the metal substrate, wherein the dielectric film comprises a polymer selected from the group consisting of polyimide, liquid crystal polymer, and polycarbonate, wherein the dielectric film has an original thickness of about 25 μm or greater And a flexure assembly of the hard disk drive. The article of claim 1, wherein the dielectric film is a polyimide having carboxyl ester structural units in the polymer backbone. The article of claim 1, wherein the dielectric film is attached to the metal substrate by an adhesive layer. The article of claim 1, wherein the dielectric film is a liquid crystal polymer attached to a metal substrate without an adhesive layer. The article of claim 1, wherein the dielectric film is etched to a thickness of less than about 10 μm. The article of claim 1, further comprising a patterned conductive layer over the dielectric film. The article of claim 1 comprising at least one unsupported cantilever lead. Providing a metal substrate; Attaching a dielectric film to the metal substrate, the dielectric film comprising a polymer selected from the group consisting of polyimide, liquid crystal polymer, and polycarbonate, the dielectric film having a thickness of at least about 25 μm; Etching the dielectric film to a thickness of less than about 20 μm. The method of claim 8, wherein the dielectric film is a polyimide having carboxyl ester structural units in the polymer backbone. The method of claim 8, wherein the dielectric film is attached to the metal substrate by an adhesive layer. The method of claim 8, wherein the dielectric film is a liquid crystal polymer attached to a metal substrate without an adhesive layer. The method of claim 10, wherein the dielectric film is etched to a thickness of less than about 10 μm. The method of claim 8, wherein the dielectric film is About 30 wt% to about 55 wt% alkali metal salt; And About 10% to about 35% by weight solubilizer dissolved in solution Etching with an aqueous solution comprising. The method of claim 8, wherein the alkali metal salt is selected from the group consisting of sodium hydroxide and potassium hydroxide. The method of claim 8, wherein the solubilizer is an amine. The method of claim 8, wherein the solubilizer is ethanolamine. The method of claim 8, wherein the etching is performed at a temperature of about 50 ° C. to about 120 ° C. 10.

Images