MXPA06009604A - Etched dielectric film in hard disk drives - Google Patents

Abstract

An etched dielectric film for use in a hard disk drive. The dielectric film has a thickness of about 25µm or greater when it is attached to a supporting metal substrate, and is subsequently etched to a thickness of about 20µm or less.

Description

DIELECTRIC FILM RECORDED IN HARD DISK UNITS Field of the Invention The invention relates to dielectric films useful in hard disk drives.

BACKGROUND OF THE INVENTION A pattern of printed polymer or copper etched into a polymeric film base can be referred to as a flexible, printed flexible circuit or wiring. Originally designed to replace bulky wiring harnesses, flexible circuitry is often the only solution for the miniaturization and movement required for today's innovative electronic assemblies. Slim, lightweight and ideal for complicated devices, flexible circuit design solutions range from single-sided conductive routes to complex, multi-layered, three-dimensional packages. Additionally, flexible circuits are used in hard disk drives. Modern computers require media in which digital data can be stored and quickly retrieved. The magnetic (hard) layers in the discs have proven to be a reliable means of storing and recovering data quickly and reliably.

REF: 175274 Disk drives that read data from, and write data to, hard drives have become popular components of computer systems. To access the memory locations on a disk, a read / write head (also referred to as a "sliding device") is provided slightly above the surface of the disk as long as the disk rotates below the head of the disk. reading / writing at an essentially constant speed. By moving the read / write head radially on the rotating disk, all the memory locations on the disk can be accessed. The read / write head is typically referred to as a "flying" head because it includes a slidable device configured aerodynamically to fly above the surface at an air location located between the disk and the sliding device that is formed according to the disk It rotates at high speeds. The air location supports the read / write head above the disk surface at a height referred to as "the flight height". A flexible circuit provides connection to the magnetic head carried by the sliding device of a disk drive suspension assembly. This overcomes the difficulties of connecting the circuitry of the disk drive to the small magneto-resistive (MR) recording heads.

Brief Description of the Invention One aspect of the present invention provides an article comprising: a flexure assembly of a hard disk drive comprising a metal substrate and a dielectric layer bonded to the metal substrate, the dielectric film comprising a polymer selected from the group consisting of polyimides, liquid crystal polymers, and polycarbonates, wherein the dielectric film has been etched to a thickness of less than about 20 μm from an original thickness of about 25 μm or greater. Another aspect of the present invention provides a method comprising: providing a metal substrate, bonding a dielectric film to the metal substrate, the dielectric film comprising a polymer selected from the group consisting of polyimides, liquid crystal polymers, and polycarbonates, the film having a thickness of about 25 μm or greater, etch the dielectric film to a thickness of less than about 20 μm. Unless stated otherwise, the concentrations of the components are presented in terms of% by weight.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates a flexible support for a head cardan suspension mounting of a hard disk drive. Figures 2a-2m illustrate the steps, including a method of the present invention, to develop a flexure structure for a hard disk drive.

Detailed Description of the Invention As required, the details of the present invention are described herein; however, it is to be understood that the modalities described are exemplary only. Therefore, the specific functional and structural details described herein are not proposed as limiting, but only as a basis for the claims and as a representative basis for teaching a person skilled in the art to variously employ the present invention .

Hard Disk Drives (HDD and Flexible Supports) The starting materials for making flexible hard drive integrated holders typically comprise a metal support layer having a molded dielectric layer (i.e., solvent-coated) or a carrier backing layer. metal and a thick dielectric layer, adhesively bonded together While the molding of a film can provide a quick method for obtaining a thin film having a particular desired thickness, these types of film also have disadvantages. recording the molded films, which makes structuring the dielectric film difficult, On the contrary, aspects of the present invention allow the selection and use of dielectric films (and adhesives, if applicable) that are easily recordable. Flexible circuits use dielectric substrate materials that are more than 25 m thick. The management and automated film processing less than 50 microns thick is known to be difficult and therefore is not profitable. Flexible circuits such as bending flex 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 substrates can be etched uniformly to provide a thin dielectric layer. In some embodiments, additional thinning of only the selected regions or characteristics of the substrate may be useful. For example, chemical etching to form holes without exit in flexible circuit substrates can be advantageous because it allows the formation of conductor structures, unsupported or cantilevers, which can not be produced by conventional physical methods. The flexible support of a head suspension assembly (HSA) represents a structural element of a hard disk drive that can be manufactured using a multi-layer composite product. A flexible support, as described in the English abbreviations 5,701,218 and 5,956,212, comprises a stainless steel layer for mechanical strength, a polyimide layer for electrical insulation and a ductile copper layer for electrical transmission. Flexible suspension supports should be made using very uniform materials, which can be customized to have small but very uniform characteristics. Because the degree of rigidity is critical to the performance of the flexible support, the thicknesses of the materials are very critical. The need for an increased data density requires that the read / write head fly low. Typical heads at 60-90 GB / sq in data capacity are currently required to fly at less than 10 nm above the rotating medium. This requires that the absolute rigidity of the flexible support be reduced. The reduction of the thickness of the flexible layer and the reduction of the weight of the composite product allows the construction of flexible supports that have improved flexibility.

The base material of the flexible support is typically a sheet of stainless steel, laminated and tempered to produce a uniform, fine grain structure and at least one hard XA condition. It preferably has a very uniform thickness in the range of 12-25 μm. The steel surface is typically recorded to produce a fine regular texture of 0.1-0.5 μm RMS. A commonly used stainless steel material is grade 302 or 304 steel from A.I.S.I. (American Iron and Steel Institute) non-magnetic, which has a thickness of 25 μm (1.0 mils), such as type 304 H-5A MW produced by Nippon Steel, Tokyo, Japan, for HDD applications. A flexible support can be produced by starting with a composite laminate product having a stainless steel layer for mechanical strength, and a dielectric polymer layer to provide an electrically insulating carrier for the conductive traces formed on the surface of the dielectric polymer layer and either by plating techniques with additive or subtraction processing. Any method produces the circuit structure necessary for the interconnection of a magneto-resistive read / write (MR) head to a hard disk drive. Figure 1 illustrates a flexible support 110 made in accordance with the present invention. The flexible support 110 comprises a flexible circuit interconnection 120, which supports the metallic trace layers 122 and is joined to the metal support structure 130. Also the cardan suspension arms 132 and the tongue 134 are portions of the metal support layer 130. The sealing layer polymer 124 protects the portions of the flexible circuit interconnection 120.

Engraver The highly alkaline developer solution, referred to herein as a recorder, comprises an alkali metal salt and optionally a solubilizer. A solution of only the alkali metal salt can be used as a recorder for polyimide but has a low engraving speed when recording LCP and polycarbonate. However, when a solubilizer is combined with the alkali metal salt recorder, it can be used to effectively etch polyimide copolymers having carboxylic ester units in the polymeric structure, LCP, and polycarbonates. Water soluble salts suitable 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 and mixtures thereof. same. Useful alkaline etchants include aqueous solutions of alkali metal salts including alkali metal hydroxides, particularly potassium hydroxides, and mixtures thereof with amines, as described in 6,611,046 Bl and 6,403,211 Bl. The useful concentrations of the recording solutions vary depending on the thickness of the polycarbonate film to be etched, as well as the type and thickness of the photoprotective substance chosen. Useful concentrations, typical of a suitable salt, vary in one embodiment from about 30% by weight to 55% by weight and in another embodiment from about 40% by weight to about 50% by weight. Useful concentrations, typical of a suitable solubilizer, vary in one embodiment from about 10% by weight to about 35% by weight and in another embodiment from about 15% by weight to about 30% by weight. The use of KOH with a solubilizer is preferred to produce a highly alkaline solution because the recorders containing KOH provide optimally recorded characteristics in the shortest amount of time. The etching solution is generally at a temperature from about 50 ° C (122 ° F) to about 120 ° C (248 ° F), preferably from about 70 ° C (160 ° F) to about 95 ° C (200 ° C). ° F) during engraving. Typically, the solubilizer in the recording solution is an amine compound, preferably an alkanolamine. The solubilizers for the recording solutions according to the present invention can be chosen from the group consisting of amines, including ethylene diamine, propylene diamine, ethyl amine, methylethylamine and alkanolamines such as ethanolamine, diethanolamine, propanolamine, and the like. The recording solution, which includes the -amine solubilizer, according to the present invention works more effectively within the percentage ranges referred to above. This suggests that there may be a double mechanism at work to etch polycarbonates or glass polymers. liquid, that is, the amine acts as a solubilizer for the polycarbonate or liquid crystal polymers most effectively within a limited range of concentrations of the alkali metal salt in aqueous solution. The discovery of this most effective range of recording solutions allows the fabrication of flexible printed circuits based on polycarbonates or liquid crystal polymers that have finely structured characteristics, which previously could not be achieved, using the normal methods of drilling, drilling and ablation with To be. Under the etching conditions, the unmasked areas of a dielectric film substrate become soluble by the action of the solubilizer in the presence of a sufficiently concentrated aqueous solution of, for example, an alkali metal salt. The time required for the engraving depends on the type and thickness of the polycarbonate film to be engraved, the composition of the etching solution, the engraving temperature, the pressure of the expression, and the desired depth of the engraved region.

Materials The present invention provides a recorded dielectric film for use in a flexible hard drive circuit. The engraving of films to introduce regions of controlled thickness, is more effective with films that do not inflate in the presence of alkaline recording solutions. The dielectric films of the present invention can be polycarbonates, liquid crystal polymers, or polyimides, including polyimide copolymers having carboxylic ester units in the polymeric structure. Preferably, the film that is recorded is cured in a substantially complete manner. The current manufacturing processes of continuous flexible circuits, roll by roll, use a base dielectric substrate that is 25 μm thick. However, manufacturers of hard drives are demanding thinner dielectric layers that have a thickness of 15 μm, 12.5 μm, 10 μm or less for better flexibility. The thickness of the dielectric film substrate can be related to the level of difficulty associated with the processing and processing of the flexible circuit. If the film web is less than about 25 μm thick, problems with material handling can lead to difficulties in the consistent fabrication of circuit structures. Unsupported films of uniform thickness less than 25 μm tend to stretch irreversibly or otherwise distort during the multi-step process of producing printed circuits. This problem can be overcome by using dielectric films according to the present invention in which thinning to less than 25 μm in thickness can occur after the film has adhered to a metallic substrate such that the metallic substrate supports the thinned dielectric layer allowing it to be processed through the manufacturing processes of continuous flexible circuits, roll by roll. Alternatively, the applications for the highly flexible dielectric film substrates, which have thinned regions, include suspension structure for hard disk drives. In hard disk applications, a flexible circuit can be made of a 25 μm film, but the flexible circuit portion in the area of the head cardan suspension assembly can advantageously have a thickness of 15 μm, 12.5 μm, μm or less for better flexibility. The existence of engraving for controlled depth of dielectric materials contributes to the improvement in applications of hard drives. For example, in hard drive applications, the main portion of a flexible circuit can be made from a dielectric film of 25 μm. The reduction in thickness to approximately 12.5 μm provides a dielectric substrate that has reduced rigidity in the mounting region of cardan head suspension of the circuit. The reduction in stiffness minimizes the influence of the dielectric film on the mechanical attributes of the hard drive's suspension. The reduction of the influence of the dielectric film leads to less variation in the flight weight of the read / write head. This increases the strength of the signal, allowing greater signal area density, which allows greater memory capacity. The thinning of the film also facilitates the use of a less powerful motor in disk drives, very sensitive to power laptops. Polyimide The polyimide film is a substrate commonly used for flexible circuits. ue meet the requirements of complex, innovative electronic assemblies. The film has excellent properties such as thermal stability and low dielectric constant. As described in U.S. Patent No. 6,611,046 Bl it is possible to produce chemically etched pathways and chemically etched through holes in flexible polyimide circuits, as needed for electrical interconnection between the circuit and a printed circuit board. It is relatively common, the complete removal of the polyimide material, for the formation of holes. Controlled etching without hole formation is very difficult when the commonly used polyimide films are inflated in an uncontrolled manner in the presence of conventional recording solutions. The most commercially available polyimide film comprises monomers of pyromanic dianhydride (PMDA), or oxydianiline (ODA), or diphenyl dianhydride (BPDA), or phenylene diamine (PPD). Polyimide polymers including one or more of these monomers can be used to produce film products designated under the trade name films KAPTON H, K, E (available from EI du Pont de Nemours and Company, Circleville, OH) and APICAL AV films. , NP (available from Kaneka Corporation, Otsu, Japan). Films of this type are inflated in the presence of conventional chemical engravers. Inflation changes the thickness of the film and can cause localized delamination of the protective substance. This can lead to loss of control of the thickness of the recorded film and irregular shaped characteristics due to the migration of the recorder to the delaminated areas. In contrast to other known polyimide films, there is evidence showing controllable thinning of APICAL HPNF films (available from Kaneka Corporation, Otsu, Japan). The existence of carboxylic ester structural units in the polymeric structure of an APICAL HPNF film that is not inflated means a difference between this polyimide and other polyimide polymers that are known to inflate or swell upon contact with alkaline etchants. The polyimide film APICAL HPNF is believed to be a copolymer derived from its structure containing ester units from the polymerization of monomers including p-phenylene-bis (trimethyl ester monoester anhydride). Other polyimide polymers containing ester units are not known commercially. However, for one skilled in the art, it would be reasonable to synthesize other polyimide polymers containing ester units depending on the selection of monomers similar to those used for APICAL HPNF. These syntheses can extend the variety of polyimide polymers for film, which, such as APICAL HPNF can be recorded in a controlled manner. Materials that can 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 (anhydrous) trimellitate), biphenol bis (anhydro trimellitate), oxy diphenol bis (anhydro trimellitate), bis (4-hydroxyphenyl sulfide) bis (anhydro trimellitate), bis (4-hydroxybenzophenone) bis (anhydro trimellitate), bis (4-hydroxyphenyl-sulfone) bis (anhydro trimellitate), bis (hydroxyphenoxybenzene), 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-aminobenzoate) bis (aminobenzoate), and the like. The polyimide films can be etched using solutions of potassium hydroxide or sodium hydroxide alone, as described in U.S. Pat. 6,611,046 Bl, or using an alkaline recorder containing a solubilizer.

LCP Liquid crystal polymer (LCP) films represent suitable materials as substrates for flexible circuits that have improved high frequency performance, lower dielectric loss, and lower moisture absorption than polyimide films. The characteristics of LCP films include electrical insulation, moisture absorption less than 0.5% at saturation, a coefficient of thermal expansion that approximates that of copper used for veneered through holes, and a dielectric constant that does not exceed 3.5 the functional frequency range from 1 kHz to 45 GHz. These beneficial properties of the liquid crystal polymers were previously known but the difficulties with the procedure prevented the application of the liquid crystal polymers to the complex electronic assemblies. The recorder with the solubilizer described herein makes it possible to use the LCP film instead of polyimide as a recordable substrate for suspension flexural assemblies. A similarity between liquid crystal polymers and APICA HPNF polyimide is the presence of carboxylic ester units in both types of polymer structures. Films that do not swell or swell of liquid crystal polymers comprise aromatic polyesters including copolymers containing p-phenylethylaminomide such as BIAC film (Japan Goro-Tex Inc., Okayama-Ken, Japan) and copolymers containing p-hydroxybenzoic acid such as the LCP CT film (Kuraray Co., Ltd, Okayama, Japan). Some embodiments of the present invention preferably use a laminated composite product in which the dielectric layer is extruded (and axially stretched) extruded liquid crystal polymer films. A process development, described in U.S. Patent No. 4,975,312, provided thermotropic, multiaxially (for example, biaxially oriented) thermotropic polymer films of commercially available liquid crystal polymers (LCPs) identified by the trade names VECTRA (based on naphthalene, available from Hoechst Celanese Corp.) and XYDAR (based on biphenol, available from Amoco Performance Products). Multiaxially oriented LCP films of this type represent suitable substrates for printed flexible circuits and circuit interconnections suitable for the production of device assemblies such as suspension bending assemblies used in hard disk drives. The development of multiaxially oriented LCP films, while providing a film substrate for flexible circuits and related devices, was subject to limitations in the methods for forming and joining these flexible circuits. A major limitation was the lack of a chemical etching method for use with LCP. Without this technique, complex circuit structures such as cantilevered, unsupported conductors or through holes or ways having angled side walls can not be included in a printed circuit design.

Polycarbonate Polycarbonates also have lower water absorption than polyimide and lower dielectric dissipation, which are very important properties for high frequency (GHz) applications, such as for microwave or wireless communication devices. While the polycarbonate films can be etched using solutions of potassium hydroxide and sodium hydroxide alone, the engraving speed is slow so that the surface of the film can be effectively etched. Engraving capabilities to produce printed flexible circuits having thinned polycarbonate substrates or polycarbonate substrates with selectively formed voids and / or tooth regions require specific materials and specific process capabilities not described above. Until now, the low cost structuring of polycarbonate film has been a key issue that prevents polycarbonate films from being applied in high volume applications. Nevertheless, as described and taught herein, polycarbonates can be easily etched when a solubilizer is combined with aqueous, highly alkaline, etching solutions, comprising, for example, water-soluble salts of alkali metals and ammonia. Engraving films to introduce accurately formed voids, depressions and other regions of controlled thickness requires the use of a film that does not inflate or swell in the presence of alkaline recording solutions. Inflation changes the thickness of the film and can cause localized delamination of the protective substance. This can lead to loss of control of the thickness of the recorded film and irregular shaped characteristics due to the migration of the recorder to the delaminated areas. The controlled etching of the films, according to the present invention) is very successful with polymers that substantially do not inflate. "Substantially not inflating" refers to a film that is inflated by a negligible amount when exposed to an alkaline etchant so as not to impede the thickening action of the etching process. For example, when exposed to some recording solutions, some polyimides will be inflated or inflated to a degree such that their thickness can not be effectively controlled in the reduction. Examples of suitable polycarbonate materials that do not inflate include substituted and unsubstituted polycarbonates. Polycarbonate blends such as aliphatic polycarbonate / polyester blends, including blends available under the trade name XYLEX from GE Plastics, Pittsfield, MA, polycarbonate / polyethylene terephthalate blends (PC / PET), polycarbonate / polybutylene terephthalate blends (PC / PBT) , and polycarbonate / poly (ethylene-2, 2-naphthalene) blends (PPC / PBT, PC / PEN), and any other polycarbonate blend with. a thermoplastic resin; 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 laminated polycarbonate product. This laminated product may have at least two different polycarbonate layers adjacent to each other or may have at least one polycarbonate layer adjacent to a layer of thermoplastic material (eg, LEXAN GS125DL which is a polyvinyl polycarbonate / polyvinyl fluoride laminate from GE). PLastics). The polycarbonate materials may also be filled with carbon black, silica, alumina and the like which may contain additives such as flame retardants, UV stabilizers, pigment and the like.

Adhesive Flexible supports for trace suspension assemblies (TSA) can use a laminate material comprising a metal layer, for example, stainless steel sheet (SST) bonded to a polyimide or polycarbonate polymer film by a bonding adhesive. The polymer film can be additionally bonded to another metal layer, for example, a copper (Cu) sheet.

Suitable adhesives include thermoplastic adhesives, such as thermoplastic polyimide (TPPI), or other chemically-recordable wet adhesive. The adhesive is typically applied to a very thin layer, for example, in the range of about 0.5 to about 5 μm thick. The dielectric layer coated with adhesive is typically laminated to a stainless steel sheet by heating both layers at temperatures typically within 20 ° C, with each other, but at approximately 30 to 60 ° C above the Tg of the adhesive material, then pressing together the layers, using plates or opposite heated rollers, to force - the adhesive flows to the surface texture of the stainless steel. The desired adhesion as measured at room temperature using the adhesion screening tests to 180 ° of industrial standard needs to be greater than 2 pounds per linear inch (pli).

Non-adhesive As an alternative to a bonded laminate, composite structures can be used to form a flexible support for a hard drive. Thermoplastic films, such as liquid crystal polymers and polycarbonate, are suitable to form a composite structure without the use of an adhesive. The thermoplastic films can be attached to a metal support sheet, such stainless steel, by using an etching solution containing an alkali metal salt and solubilizer to etch a surface of the film. A metal foil having at least one surface treated with acid will form a bond to the surface treated with etchant at the application of about 100 psi to about 500 psi pressure to the metal backing sheet and the thermoplastic film at temperatures that cause the thermoplastic film to flow. The binding surface of the metal foil is typically treated with a strongly acidic etchant composition. Acid etchers suitable 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 can also be treated with a recorder so that it can be attached to a second metal foil. The international application WO 00/23987 describes the use of a high temperature lamination press to form a laminated product having a molten liquid crystal polymer for the bond between a stainless steel sheet and a copper sheet. This three-layer material can be useful for suspension bending applications (FOS), stroke suspension mounts (TSA), and suspension assembly of related disk drives. Alternatively, the second side of the thermoplastic-metal laminate can be treated with a recorder to make the surface suitable for metallization. This metallization process can include deposits without electrodes or vacuum deposition of a seed coat to be augmented with additional layers of metal using conventional plating techniques. When metal plating without electrodes is used, the process for producing a metal-plated thermoplastic-metal laminate can comprise the steps of providing a thermoplastic-metal laminate substrate to which an aqueous solution is applied comprising from about 30% by weight to about 50% by weight of potassium hydroxide and from about 10% by weight to about 35% by weight, to provide a laminated thermoplastic-metal substrate, etched. The application of a solution of tin (II) to the laminated substrate of thermoplastic-metal, engraved, followed by palladium (II) solution, provides the engraved product of thermoplastic-metal, seeded with metal. The bonding improvement between the thermoplastic-metal laminate and the support metal on one side and the metal-seeded layer on the other adds the integrity and durability of a composite structure. The metal-seeded layer further provides the alternative for forming printed circuits using an additive process instead of a subtractive process commonly used to form electrically conductive traces on carrier substrates.

Process for Making Circuits In addition to reducing the total thickness of a dielectric polymer film, the engravers described herein can be used to form various characteristics of dielectric films. The formation of recessed or thinned regions, unsupported conductors, through holes and other circuit characteristics in the film, typically require the protection of portions of the polymeric film using a mask of a photoprotective, processable, aqueous, negatively engraved substance. photo-reticulate, or a metal mask. During the etching process, the photoprotective substance does not exhibit substantially swelling or delamination of the dielectric film. Negative photoprotective substances suitable for use with dielectric films according to the present invention include, water-repellent, discoverable, photopolymer compositions, such as those described in U.S. Patent Nos. 3,469,982; 3,448,098; 3,867,153; and 3,526,504. These photoprotective substances include at least one polymer matrix including crosslinkable monomers and a photoinitiator. Polymers typically used in the photoprotective substance include copolymers of methyl methacrylate, ethyl acrylate and acrylic acid, copolymers of styrene and isobutyl maleic anhydride ester and the like. The crosslinkable monomers may be multiacrylates such as trimethylolpropane triacrylate. The water-soluble, regulatable, sodium carbonate, eg, water-based commercially available, photoprotective substances employed in accordance with the present invention include photoprotective, polymethyl-methacrylate materials, such as those available under the RISTON commercial designation of. E.I. DuPont de Nemours and Co., for example, RISTON 4720. Other useful examples include AP850 available from LeaRonal, Inc., Freeport, NY, and PHOTEC HU350 available from Hitachi Chemical Co., Ltd. Low dry film photoresist compositions The commercial name AQUA MER are available from MacDermid, Waterbury, CT. There are several series of AQUA MER photoprotective substances that include the "SF" and "CF" series with SF120, SF125 and CF2.0 that are representative of these materials. The dielectric film of the polymer-metal laminate can be chemically etched in several stages in the manufacturing process of flexible circuits. The introduction of an etching step before the production sequence can be used to thin the bulky film or only selected areas of the film while leaving the volume of the film in its original thickness. Alternatively, the thinning of the selected areas of the film later in the flexible circuit fabrication process may have the benefit of introducing other circuit characteristics before altering the thickness of the film. Despite the occurrence of selective thinning of the substrate in the process, the handling characteristics of the film remain similar to those associated with the production of conventional flexible circuits. Figures 2a-2m illustrate a method for making a thin shrink suspension assembly of the present invention. Figure 2a shows a metal substrate 210, which is typically a stainless steel sheet, in which a layer of dielectric material 212 is laminated to form a laminated weft structure. The dielectric layer can be laminated to the metal sheet by using an adhesive or by melt-bonding a thermoplastic dielectric film. If an adhesive is used, a suitable adhesive can be a wet etched chemical such as TPPI, available under the trade name PIXEO from Kaneka, Tokyo, Japan. The stainless steel sheet is typically 12 μm to 50 μm thick, and in other embodiments from 18 μm to 25 μm thick.

The dielectric layer is typically from about 25 μm to about 75 μm thick. The thickness of the adhesive is typically from about 2 μm to about 5 μm. The laminated web structure is then passed through an etching bath, which dissolves the dielectric film layer, to form a thin dielectric layer 212 ', as illustrated in Figure 2b. The engraving bath contains a recording solution suitable for the type of dielectric layer applied to the metal sheet, as taught above. The process can provide uniform engraving depths in the directions transverse to the weft and below the weft. The laminated web is then placed in a sizzling chamber where a thin conductive layer is applied to the dielectric surface. The thickness of the sputtered layer is typically from about 10 nm to about 200 nm. Typical materials used for this process include, but are not limited to, Ni, Cr and a metallic Ni / Co / Cu alloy available under the tradename MONEL from Special Metals Corporation, New Hartford, NY, or other materials with high Melting points that are suitable for sizzle application. The weft is then placed in a plating bath to accumulate the conductive layer to a total thickness of about 1 μm to about 5 μm to make it stronger to handle in the subsequent processes (and to make it act as a low-field metal). resistance during the subsequent steps of electroplating). Typical plating materials include copper and nickel. Figure 2c illustrates the web laminated with the metal layer 214. A semi-additive process can then be used to produce the circuits of the laminated web. The surface layer can be cleaned first, for example with a solution of potassium peroxymonosulfate, such as that available under the trade name SUREETCH from E.I. du Pont de Nemours, Wilmington, DE. Then the photo-protective substance layer 218, which may be wet or dry, is applied to the metallic substrate 210 and the photo-protective substance layer 216 is applied to the metallic layer 214. The photoprotective substance layers are then imaged by exposure to radiation and reveal themselves to form circuit patterns as illustrated in Figure 2d. The pattern of the photoprotective substance restricts the subsequent metallic electroplating to specific areas. Typically, the edges of the metallic characteristics of the circuit pattern are well defined by the photoprotective substance, thus making it possible to have narrow width and narrow shrinkage characteristics. To provide closed alignment between the patterns of the strokes that will be created in the metallic layer 240 and the characteristics recorded in the metal substrate 210, the layers 216 and 218 of photoprotective substance can be formed in images at the same time using aligned photo-tools. The next step, as illustrated in Figure 2e, is to plaster metal in the circuit pattern in the metal layer 214 to form the circuit traces 220. During this process, the metallic substrate 210 may be in ground potential or in polarity slightly opposite to the metal potential in the plating bath in order to prevent the metal of the conductive trace from being plated in the metal substrate 210. (Alternatively , the metal substrate 210 can be protected by the photoprotective substance). As illustrated in Figure 2f, then another layer of photoprotective substance 222 is applied on the layer 216 of photoprotective substance and the circuit traces 220. The photoprotective substance is then exposed by flood to form the traces 220 of protected circuits with insoluble value. Then, as illustrated in Figure 2g, the portions of the metal layer 210 exposed by the layer pattern 218 of photoprotective substance are recorded to the thin dielectric layer 212 '. If the metal layer is stainless steel, suitable etchers may include ferric chloride and cupric chloride. Then, as illustrated in Figure 2h, the layer 222 of photoprotective substance and the remaining portions of the layers 216 and 218 of photoprotective substance are removed.

Once the photoprotective substance is removed, the metallic layer 214 of the underlying surface and a thin layer of traces 220 of circuits are recorded to leave the traces 220 of conductive circuits, as illustrated in Figure 2i. The following steps comprise the creation of characteristics in the thinned dielectric layer 212 A. Initially, the photoprotective substance is applied to both sides of the existing structure. The photo-tools are aligned to the metal patterns on each side of the laminated structure and both layers of photoprotective substance are imaged by exposure to adequate radiation and are revealed in the same manner as described above. This results in structured layers 224 and 226 of photoprotective substance aligned to the circuit traces 220 and the etched metal substrate 210, respectively, as illustrated in Figure 2j. Then, the exposed portions of the dielectric layer 212 are formed or removed by exposure to, for example, chemical or plasma etchers, and the remaining portions of the light protection layer layers 224 and 226 are removed to leave the flexible support structure illustrated. in Figure 2k. Suitable methods are known to those skilled in the art. Subsequently, one can apply, image and reveal another layer, or layers, on one or both sides of the structure to allow the circuit traces 220 to be encased with an additional layer of conductive material 228 suitable for dielectric bonding. or contact compatibility, for example, gold, as illustrated in Figure 21. Optionally, as a final step, a sealing layer 230 can be applied, exposed and developed to form a protective layer on the circuit traces 220, as illustrated in Figure 12m. An advantage of this process is that features can be formed anywhere in the structure in both the metal substrate 210 and the metal layer 214. This makes it possible to produce "flight" characteristics (not supported by the dielectric layer) of either electrical traces or structural elements' (for example, steel). Optionally, dielectric materials compatible with the functional requirements of the final product can be applied to the flexible support structure. The flexible support is then ready to be laminated, glued or welded to the load bar of the secondary suspension assembly to make a complete mounting of cardan head suspension for a hard drive. A similar process is the production of flexible circuits, comprising the engraving step, which can be used in conjunction with various known pre-engraving and post-engraving processes. The sequence of these procedures can be applied as desired for the particular application. A typical additive sequence of steps can be described as follows: The water-processable, photoprotective substances are laminated on both sides of a substrate comprising dielectric film with a thin side of copper, using normal lamination techniques. Typically, the substrate has a polymer film layer of about 25 μm to about 75 μm, with the copper layer being about 1 to about 5 μm thick. The thickness of the photoprotective substance is from about 10 μm to about 50 μm. In the image-type exposure of both sides of the photoprotective substance to ultraviolet light or the like, through a mask, the exposed portions of the photoprotective substance become insoluble by cross-linking. The protective substance is then revealed, by removal of the unexposed polymer with a dilute aqueous solution, for example, a 0.5-1.5% sodium carbonate solution, until the desired patterns or structures are obtained on both sides of the laminated product. The copper side of the rolled product is then additionally veneered to the desired thickness. The chemical etching of the polymer film then proceeds by placing the laminated product in a bath of recording solution, as described above, at a temperature of about 50 ° C to about 120 ° C to etch portions of the polymer not covered by the cross-linked protective substance. This exposes certain areas of the thin, original copper layer. The protective substance is then released from both sides of the rolled product in a 2-5% solution in alkali metal hydroxide from about 25 ° C to about 80 ° C, preferably from about 25 ° C to about 60 ° C. Subsequently, exposed portions of the original, thin, copper layer are recorded using a non-damaging etchant - the polymer film, for example PERMA ETCH, available from Electrochemicals, Inc. In an alternative subtractive process, the substances Water-curable, photoprotective, laminates are again laminated on both sides of a substrate having one side of polymeric film and one side of copper, using normal lamination techniques. The substrate consists of a polymer film layer of about 25 μm to about 75 μm thick with the copper layer that is about 5 μm to about 40 μm thick. The photoprotective substance is then exposed on both sides to ultraviolet light or the like, through a suitable mask, by crosslinking the exposed portions of the protective substance. The image is then developed with a dilute aqueous solution until the desired patterns or structures are obtained on both sides of the rolled product. The copper layer is then recorded to obtain the circuitry, and in this way the portions of the polymeric layer are exposed. An additional layer of aqueous photoprotective substance is then laminated onto the first protective substance on the copper side and crosslinked by flood exposure to a source of irradiation in order to protect the exposed surface of the polymer film (copper side). ) of the additional engraving. The areas of the polymeric film (on the side of the film) not covered by the cross-linked protective substance are then etched with the recording solution containing an alkali metal salt and a solubilizer at a temperature of about 70 ° C to about 120 °. C, and the photoprotective substances are then detached from both sides with the diluted basic solution, as described above. It is possible to introduce regions of controlled thickness into the dielectric layer of the flexible circuit using controlled chemical etching either before or after etching of related through holes and holes which completely removes the dielectric polymer materials as required to introduce conductive routes through of the circuit movie. The step of introducing normal gaps in a printed circuit is typically presented at about half the circuit manufacturing process. It is convenient to finish the engraving of the film in approximately the same time frame by including a step of recording to the end of the substrate and a second step of engraving to record hollow regions of controlled depth. This can be achieved by proper use of the photoprotective substance, reticulate to a pattern or structure selected by exposure to ultraviolet radiation. In the development, the removal of the photoprotective substance reveals areas of dielectric film that will be recorded to introduce recessed regions. Alternatively, recessed regions may be introduced into the polymer film as an additional step after finishing other characteristics of the flexible circuit. The additional step requires lamination of the photoprotective substance on both sides of the flexible circuit followed by exposure to crosslink the photoprotective substance according to a selected pattern or structure. The development of the photoprotective substance, using the diluted alkali metal carbonate solution described above, exposes areas of the dielectric film that will be etched at controlled depths to produce associated thinned slits and film regions. After allowing a sufficient time to record the depressions of desired depth in the dielectric substrate of the flexible circuit, the photoprotective, reticulated, protective substance is released as before, and the resulting circuit, including the selectively thinned regions, is rinsed clean. The steps of the process described above can be carried out as a batch process using individual steps or in an automated way using equipment designed to transport a web material through the process sequence from a supply roll to a roll roll, that collects mass produced circuits that include selectively thinned regions and controlled depth slits in the polymer film. The automated processing uses a weft management device having a variety of processing stations for applying, exposing and revealing coatings of photoprotective substance, as well as etching and plating the metal parts and etching the polymer film of the starting material. to the laminated polymer product. The engraving stations include several spray bars such as jet sprayers that spray recorder in the motion frame to record those parts of the frame. not protected by the reticulated photoprotective substance. To create finished products such as flexible circuits, interconnecting tape for " " processes (automated tape joining), microflexible circuits, and the like, conventional processing can be used to add multiple layers and areas of copper plate with gold, tin or nickel for subsequent welding procedures and the like as required for reliable interconnection of devices.

Examples Examples 1-4 Materials Polymer film substrates A. BIAC Film.- 25 μm thick liquid crystal polymer (LCP) film is produced by Japan Gore-Tex Inc., Okayama-Ken, Japan. B. APICAL film HPNF (50 micron film) is produced by Kaneka Corporation, Otsu, Japan.

Compositions Recorders AA. 33% by weight of potassium hydroxide + 19% by weight of ethanolamine + 48% by weight of deionized water. BB. 45% by weight of potassium hydroxide + 55% by weight of deionized water. DC. 35% by weight of. potassium hydroxide + 15% by weight of ethanolamine + 50% by weight of deionized water.

Photoprotective Substance A dry film protective substance was used for selective placement of regions for controlled etching. The photoresist material is available from MacDermid Inc., of Waterbury, CT under the product numbers SF310, SF 315 or SF 320. "Table 1 provides evidence that the 25 μm liquid crystal polymer film and the film 50 μm polyimide comprising a polymer derived from p-phenylene-bis monomer (trimellitic acid monoester anhydride) can be operated using conventional automated equipment to produce flexible circuits During the flexible circuit production process, the indicated recorders in the table they were sprayed automatically for controlled thinning of regions of the film that were exposed by selective removal of the photoprotective substance.These recessed areas produced having a film thickness that was reduced to 25% to 50% of the original film thickness.

Table 1 Polyimide and Liquid Crystal Polymer The partial thinning method of the present invention can be very precise. For example, • Example 4 was a rolled product of stainless steel and 50 mm of APICAL film. HPNF was etched with a 45% by weight KOH tape recorder to reduce its total thickness. The film experienced a residence time of approximately 1.5 minutes. The resulting material had an average average thickness reduction of '21 .63 μm with a standard deviation of 0.85 μm. The standard deviation of the roughness of the original APICAL HPNF film was 0.65 μm showing that the etching process was uniform transversely and down the weft with minimal effect on the surface roughness of the finished laminated weft.

Examples 5-9 and Comparative Example Cl For this series of examples, different recording solutions were used to record different types of polycarbonate films. The water-processable, photoprotective substances were laminated on both sides of a substrate having one side of polymeric film using normal lamination techniques. In the image-type exposure of both sides of the photoprotective substance to ultraviolet light or the like, through a mask, the exposed portions of the photoprotective substance became insoluble by cross-linking. The protective substance was then revealed, by removal of the unexposed polymer with a dilute aqueous solution, for example, a 0.5-1.5% sodium carbonate solution, until the desired patterns or structures were obtained on both sides of the rolled product. For examples 5, 7-9 and Cl, the films were subjected to double-sided engraving. In other words, no coatings or protective substances were applied to either side of the film, so that both sides were exposed to the recorder. To determine the engraving speed determination, a small film sample (approximately 1 cm x approximately 1 cm) was cut and immersed in a recording solution. This resulted in the sample film being recorded on both sides. The engraving speed (for two sides) was then determined by dividing the reduced thickness by half over the engraving time. For Example 6, the films were taped on one side. A photoprotective substance was laminated, processable, watery, dry on both sides of the polycarbonate film materials. One side of the protective substance was exposed by flooding and the other side was exposed under a patterned mask. The exposed functions of the photoprotective substance became insoluble by crosslinking. • The protective substance was then revealed by removal and the unexposed polymer with a dilute aqueous solution of 0.5-1.5% sodium carbonate, resulting in a polycarbonate film with a solid layer of protective substance on one side and a layer with protective substance patterns on the other side. The speeds for the engraving of an individual side of a sample are shown later in Table 3. For engraving on one side, for example, when one side is covered with light-protecting substance, the engraving speed will be half the speed of the engraving of two sides. For polycarbonate films with protective substances, one side of the protective substance (two thousandths of an inch thick) was exposed by flooding first and the other side was exposed under a mask and then revealed.

All the engraving experiments were carried out in a laboratory beaker, without stirring, using a water bath at 85 ° C unless specifically noted otherwise. The etch results for the polycarbonate films are summarized in Table 3. The recording compositions are shown in Table 3 as the ratio of KOH to • solubilizer (ethanolamine) with the rest of the composition which is water unless otherwise specified. For example, Example 5 shows "45/20" in the recorder column, which indicates a recording composition of 45% by weight of KOH, 20% by weight of ethanolamine, and the remainder is water. The designations "A" through "I" correspond to the polycarbonate films designated A through I in Table 2 below.

Table 2 Polycarbonate films Name Commercial thickness of Chemical composition of Available material LEXAN film T2F Polycarbonate (GE Plastics finish) At 132 μm DD 112 smooth / matt) (Pittsfield Ma) LEXAN TSF Polycarbonate (finish A2 260 μm GE Plastics DD 112 smooth / matt) LEXAN TSF Polycarbonate B 254 μtn GE Plastics OQ 112 (optically clear) LEXAN FR83 Polycarbonate with C 128 μm GE Plastics 116 flame retardant XYLEX PC and D mixes 125 μm GE Plastics D7010MC aliphatic polyester XYLEX PC and blends of E 165 um GE Plastics D5010MC aliphatic polyester PC and blends of F XYLEX D56 164 μm GE Plastics aliphatic polyester Polycarbonate (filling G LEXAN 8B25 265 um GE Plastics with carbon black) Table 3 Summary of polycarbonate (PC) engraving results * Etching temperature was approximately 92 ° C + Titration result showed a real concentration of 41. 8% by weight of KOH and 20.9% by weight of ethanolamine.

It will be appreciated by those skilled in the art, in view of the present disclosure, that changes may be made to the embodiments described herein without departing from the spirit and scope of the present invention. It is noted that in relation to this date, the best method known by the applicant to carry out the present invention is that which is clear from the present description of the invention.

Claims (17)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. Article, characterized by comprising: a flexible support assembly of a hard disk drive comprising a metal substrate and a dielectric film laminated to the substrate. metallic, the dielectric film comprising a polymer selected from the group consisting of polyimide copolymers including carboxylic ester structural units in the polymeric structure, liquid crystal polymers, and polycarbonates, wherein the dielectric film has been etched to a thickness of less than about 20 μm from an original thickness of about 25 μm or greater.
2. 2. An article according to claim 1, characterized in that the dielectric film is a polyimide having carboxylic ester structural units in the polymer structure.
3. 3. Article according to claim 1, characterized in that the dielectric film is bonded to the metal substrate by a layer of adhesive.
4. 4. Article according to claim 1, characterized in that the dielectric film is a liquid crystal polymer bonded to the metal substrate without a layer of adhesive.
5. Article according to claim 1, characterized in that the dielectric film has been etched to a thickness of less than about 10 μm.
6. 6. Article according to claim 1, characterized in that it also comprises a conductive layer in patterns or structured in the dielectric layer.
7. 7. Article in accordance with the claim 1, characterized in that it includes at least one cantilever conductor, not supported.
8. 8. Method, characterized in that it comprises: providing a metallic substrate, laminating a dielectric film to the metallic substrate, the dielectric film comprising a polymer selected from the group consisting of polyimide copolymers including carboxylic ester structural units in the polymeric structure, polymers of liquid crystal, and polycarbonates, the film having a thickness of about 25 μm or greater, etch the dielectric film to a thickness of less than about 20 μm.
9. 9. Method according to claim 8, characterized in that the dielectric film is a polyimide having a carboxylic ester structural unit in the structure of the polymer.
10. Method according to claim 8, characterized in that the dielectric film is bonded to the metal substrate by a layer of adhesive.
11. Method according to claim 8, characterized in that the dielectric film is a liquid crystal polymer bonded to the metal substrate without a layer of adhesive.
12. Method according to claim 10, characterized in that the dielectric film has been etched to a thickness of less than about 10 μm.
13. Method according to claim 8, characterized in that the dielectric film is etched with an aqueous solution, comprising: about 30% by weight to about 55% by weight of an alkali metal salt; and about 10% by weight to about 35% by weight of a solubilizer dissolved in the solution.
14. 14. Method according to claim 8, characterized in that the alkali metal salt is selected from the group consisting of sodium hydroxide and potassium hydroxide.
15. 15. Method according to claim 8, characterized in that the solubilizer is an amine.
16. 16. Method according to claim 8, characterized in that the solubilizer is ethanolamine. Method according to claim 8, characterized in that the engraving is carried out at a temperature of about 50 ° C to about 120 ° C.