JP2008135164A - Manufacturing method of layered product for hard disc drive (hdd)suspension - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a layered product for a hard disk drive (HDD) suspension omitting complication of a working step and suitable for an inexpensive working method by which copper wiring lines can be finely worked. <P>SOLUTION: The manufacturing method of the layered product for the HDD suspension includes: (a) applying a solution of a polyimide based resin solution or a solution of a precursor of the polyimide based resin on a stainless layer A and drying and thermally treating the solution to form an insulating resin layer B comprising a plurality of polyimide based resin layers and having 1×10<SP>-5</SP>to 3×10<SP>-5</SP>/°C linear expansion coefficient; (b) a step for depositing a first seed layer C as a metal thin film by a sputtering method on the resin layer B; (c) a step for depositing a second seed layer D as a metal thin film having satisfactory conductivity by a sputtering method on the first seed layer C; and (d) a step for forming a plating layer E to be a conductive layer on the second seed layer D. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a suitable laminate as an HDD (Hard Disk Drive) suspension board and a method for manufacturing an HDD suspension using the same. More specifically, the present invention relates to a highly functional laminate that can be processed at low cost and with high precision in miniaturization of wiring required for a suspension material.

The technological evolution for increasing the capacity of HDDs is remarkable, and the surface recording density has been improved by the miniaturization of the slider, and the average storage capacity has reached about 40 Gbits / in ² at present. These technologies have been replaced by wire-type suspensions that use conventional wire wires instead of wireless-type suspensions that have integrated wiring, and the instability based on non-uniform wire load has been a problem. As a result, the suspension's floating posture has been greatly improved, enabling technology to mount a slider that can be downsized. By enabling the technology to mount this miniaturized slider, a technology for dramatically improving the write capacity such as track density and linear recording (bit) density has been achieved (see Non-Patent Documents 1 and 2).

Japanese Patent Laid-Open No. 2002-245609 JP 2000-339650 A JP 2000-195032 A JP 2001-352137 A IDEMA Japan News No47.p8- Nikkei Electronics 1998.4.6.p713- IDEMA Japan News No45.p6-

  However, the technical needs for increasing the capacity of HDDs do not seem to stop, and technological development aimed at further increasing the capacity mainly for video applications is progressing. Specifically, a method of improving the storage capacity by further downsizing the slider, or introducing a microactuator that enables minute movement of the slider by dividing the movement of the arm into multiple stages, and further a chip (amplifier) Proposals have been made for new technologies such as chip-on-suspension, in which the is mounted directly on the suspension. With the advent of these microactuators and chip-on-suspensions, the number of wires used to control them has increased, and at the same time, the suspension itself and the slider have become more compact. (See Non-Patent Documents 2 and 3).

  As a technique for processing this fine wiring, after forming polyamic acid which is a precursor of polyimide resin on a stainless steel foil and processing it into a predetermined shape, it is replaced with polyimide resin by thermosetting, and then by a sputter plating method. Techniques such as an additive method for forming wiring (CIS method) and a FOS method in which a sputter-plating is performed on a polyimide resin and then directly bonded onto the load beam using an adhesive are proposed. However, these technologies, after forming fine wiring, to form a part of the copper wiring called a flying lead, which is necessary for connecting the slider and the terminal and the wiring further, the polyimide resin under the wiring is laser processing method etc. This method has to be removed by using this method, and there is a problem that the subsequent process becomes complicated and the cost increases. In addition, since the FOS method is directly attached onto a load beam, which is a support substrate, using an adhesive, positional accuracy is required, and it is said that it is technically difficult to apply to this miniaturized slider. Furthermore, until now, flexure blanks, called the short tail type, where a relay cable is retrofitted to a flexure blank, have been the mainstream, but from the viewpoint of yield during mounting processing, this short tail and the relay cable are integrated into a long tail type. It is moving to. As a result, the number of flying parts of the copper wiring alone necessary for connection to each terminal increases, and the complexity in the subsequent process is further increased.

  By the way, although patent document 1 teaches using the laminated body which laminated | stacked the polyimide layer and the copper foil sequentially on the stainless steel foil as an object for suspensions, copper foil is a method of laminating | stacking by the press-bonding method. Patent Document 2 discloses a method of manufacturing a suspension from a three-layer laminate similar to Patent Document 1. Patent Document 3 obtains a laminate in which a polyimide precursor layer and a copper foil layer are sequentially formed on a stainless steel foil, forms a wiring pattern by a subtractive method, and then forms a polyimide precursor layer by a photolithographic technique. A method for manufacturing a suspension including a step of imidizing after patterning is disclosed. Here, the copper foil layer is formed on the polyimide precursor layer. In addition to the hot press method, a metal thin film such as copper is formed by sputtering, and metal plating such as electrolytic copper foil is further formed thereon. The method of applying is illustrated. Patent Document 4 discloses a technique related to improvement of the peripheral structure of the suspension. Patent Documents 3 and 4 and Non-Patent Document 2 teach that there are a subtractive method, an additive method, a semi-additive method, etc. as suspension manufacturing techniques, and three layers comprising a stainless steel foil, a polyimide layer, and a copper foil. It is disclosed that this laminate is useful for the subtractive method and the semi-additive method.

  An object of the present invention is to provide a laminate material suitable for an inexpensive processing method capable of omitting the complexity of a process when processing into a flexure blank and finely processing a copper wiring.

  As a result of intensive studies to solve such problems, the present inventors have formed a polyimide resin on a stainless steel foil, and further processed the polyimide resin directly by etching the metal by sputtering-plating. Thus, the inventors have found that a suitable material that can be processed at low cost without requiring post-processing by laser beam irradiation or the like is obtained, and the present invention has been completed.

That is, the present invention is a method for manufacturing a laminate for an HDD suspension comprising a stainless steel layer A, an insulating resin layer B, a seed layer, and a plating layer E.
a) On the stainless steel layer A, a polyimide resin solution or a precursor solution thereof is applied, dried and heat-treated to form an insulating resin layer B composed of a plurality of polyimide resin layers. The expansion coefficient is 1 × 10 ^{−5 to} 3 × 10 ⁻⁵ / ° C., and the layers on both sides are polyimide resin layers having a glass transition temperature of 300 ° C. or lower.
b) forming a first seed layer C as a metal thin film on the insulating resin layer B by sputtering;
c) forming a second seed layer D as a metal thin film having better conductivity than the metal thin film of the first seed layer C on the first seed layer C by sputtering;
d) forming a plating layer E to be a conductor layer on the second seed layer D;
The manufacturing method of the laminated body for HDD suspension characterized by including each process of these.

In the present invention, satisfying any one or more of the following provides a preferable method for producing a laminate for an HDD suspension.
1) The adhesion between the first seed layer C and the second seed layer D and the adhesion between the second seed layer D and the plating layer E are both 0.6 kN / m or more.
2) The first seed layer C is a metal layer made of Cr, Mo, Ni, Ti, Be, Si or an alloy thereof having a thickness of 2 to 10 nm.
3) The second seed layer D is a metal layer having a thickness of 100 to 300 nm, and the first seed layer C is a metal layer having a thickness of 2 to 30 nm.
4) The plating layer E is made of a metal layer made of copper having a thickness of 5 to 15 μm or a copper alloy containing copper as a main component.
5) The insulating resin layer B is a polyimide resin layer having a thickness of 5 to 18 μm, and its linear expansion coefficient is 1 × 10 ^{−5 to} 3 × 10 ⁻⁵ / ° C.
6) The stainless steel layer is made of SUS304 having a thickness of 5 to 30 μm.

Further, the present invention provides a method for manufacturing an HDD suspension,
e) preparing the HDD suspension laminate obtained by the HDD suspension laminate manufacturing method described above;
f) using the resist as a mask on the surface of the plating layer E, etching the exposed plating layer, removing the resist, and forming a plating layer having a pattern on the insulating resin layer B; and
g) removing unnecessary portions of the insulating resin layer B to form an insulating resin layer having a pattern;
A method for manufacturing an HDD suspension, comprising the steps of:

Hereinafter, a method for producing a laminate for HDD suspension (hereinafter also referred to as a laminate) of the present invention will be described.
The laminate obtained by the production method of the present invention comprises stainless steel foil layer A / insulating resin layer B / first seed layer C / second seed layer D / plating layer E. Hereinafter, for convenience of explaining the layer structure, the stainless steel foil layer A is on the bottom and the plating layer E is on the top.

  The stainless steel layer used in the method for manufacturing a laminate of the present invention is not particularly limited, but SUS304 annealed at a temperature of 300 ° C. or higher is particularly preferable from the viewpoint of spring characteristics and dimensional stability. The thickness of the stainless steel foil used may be in the range of 5 to 30 μm, preferably 10 to 30 μm, more preferably 15 to 25 μm. If the thickness of the stainless steel layer is less than 5 μm, rolling of the SUS foil becomes difficult and the cost becomes high, which is not practical. On the other hand, if the thickness exceeds 30 μm, it becomes difficult to adjust the buoyancy of the slider due to the rigidity of the stainless steel foil, which is not suitable.

  In addition, the insulating resin layer provided on the stainless steel layer in the present invention is preferably made of a polyimide resin system having low thermal expansion from the viewpoint of dimensional stability and warpage, but is not limited thereto. General-purpose resins such as epoxy resins are advantageous in terms of cost, but have a large coefficient of thermal expansion, so warpage is likely to occur, which is not preferable because stable position accuracy of the slider cannot be obtained due to warpage and storage capacity decreases. .

Any polyimide resin may be used as long as it has an imide bond in its structure, such as polyimide, polyamideimide, or polyetherimide. The polyimide resin layer may consist of only a single layer, but is preferably composed of a plurality of polyimide resin layers, and has good adhesion to the metal layer on both sides (surface) in contact with the metal layer. The ones shown are used and the other layers are of low thermal expansion. The polyimide resin exhibiting good adhesion to the metal layer has a glass transition temperature (Tg) of 300 ° C. or lower. In addition, the intermediate layer not in contact with the stainless steel layer or the seed layer has a dimensional change rate with respect to a temperature change, that is, a linear expansion coefficient of 30 × 10 ⁻⁶ / ° C. or less in terms of dimensional stability when processed into an HDD suspension. It is preferable to use one. The intermediate polyimide resin layer is thickened and the surface polyimide resin layer having a high linear expansion coefficient is used, and the linear expansion coefficient of the insulating resin layer as a whole is 10 × 10 ⁻⁶ to 30 × 10 ⁻⁶ / ° C. The range.

  The thickness of the insulating resin layer is preferably in the range of 5 to 18 μm. When the thickness is less than 5 μm, it is difficult to form an insulating resin layer such as a polyimide resin layer, and sufficient insulation cannot be ensured. On the other hand, if the thickness of the resin layer is 18 μm or more, the spring property for controlling the buoyancy of the slider is affected, and a stable buoyancy cannot be obtained.

  On the insulating resin layer B, a first seed layer C and a second seed layer D are sequentially laminated by a sputtering method. For the first seed layer, a metal such as Cr, Mo, Ni, Ti, Be, Si, or an alloy thereof is effective in order to ensure adhesion with the plating layer as the conductor layer. There are no particular restrictions on the metal species used for the sputter layer, but Cr, Mo or alloys containing these as the main component are particularly effective because of their high adhesion. The thickness of the first seed layer is 2 to 300 nm, preferably 2 to 30 nm, more preferably 2 to 10 nm. If the thickness of the sputtered layer is 2 nm or less, it is difficult to form a uniform film, and if the thickness is 300 nm or more, the sputtered film is undesirably cracked.

  On the first seed layer, a second seed layer D having good conductivity is provided in advance in order to facilitate the lamination of the plating layer. As the metal used for the second seed layer, Cu or Cu and a copper alloy of Cr, Mo, Ni, Ti, Be, Si are preferably used. The second seed layer is a sputtered film having a thickness of 15 to 400 nm, preferably 50 to 350 nm, more preferably 100 to 300 nm. If the thickness is 1 nm or less, current unevenness is likely to occur when a current is applied, and defects such as pinholes are likely to occur in the plating layer. On the other hand, when it is thicker than 400 nm, it tends to be brittle, and it is not preferable because cracks occur when a wiring such as a flying lead is formed alone. The conductivity of the second seed layer D is preferably a metal that is more conductive than the second seed layer C and gives a high adhesion to the plating layer E.

  The plating layer provided on the second seed layer is formed of copper or a copper alloy containing copper as a main component. Examples of the metal blended in the copper alloy include Ni, Be, Cr, Ni, Ti, Zr, and Fe. The thickness of the plating layer is 5 to 20 μm, preferably 5 to 15 μm. It is easier to finely process the copper foil wiring as the thickness of the plating layer is thinner. However, when the thickness of the plating layer is 5 μm or less, the wiring strength is weak, and disconnection of the flying lead portion is likely to occur. Moreover, when the thickness of the plating layer is 20 μm or more, it is not preferable from the viewpoint of inferior wiring strength and the like in comparison with a laminate obtained by thermocompression bonding of a copper foil.

Next, an example of the manufacturing method of the laminated body of this invention is demonstrated.
In manufacturing a laminated body, first, a polyimide resin solution is applied on a stainless steel layer serving as a base. The polyimide resin can be applied by a known method, and is usually applied using an applicator. The polyimide resin solution may be prepared by dissolving an imidized polyimide resin in a solvent. In the present invention, a polyimide resin precursor solution is used, and after application, the solvent is removed by preheating. A method of imidization by heat treatment after removing (drying) to some extent is preferable. In addition, when using the imidized polyimide resin solution, naturally, the heat treatment for imidization is omitted. Thus, after forming a polyimide-type resin layer, a 1st seed layer is formed on this polyimide-type resin layer as a metal thin film which shows adhesiveness with a polyimide resin by a sputtering method. Next, a second seed layer is formed as a conductive metal thin film on the first seed layer formed here. By forming the second seed layer, the formation of the plating layer by the electrolytic-plating method is facilitated. Next, a plating layer to be a conductor layer is formed on the second seed layer.

Next, a method for manufacturing the HDD suspension of the present invention will be described.
The HDD suspension is obtained by laminating or coating a photosensitive resist on the surface of the laminate composed of the stainless steel layer, resin layer, first seed layer, second seed layer, and plating layer obtained as described above, and exposing and developing. Then, the exposed plating layer is etched using the photosensitive resist as a mask to remove unnecessary portions, and then the photosensitive layer is peeled and removed to form a desired pattern on the resin layer. Next, unnecessary portions of the exposed resin layer are removed with a laser beam using the plating layer as a mask to form an insulating layer having a desired pattern. Further, a photosensitive resist is laminated or applied to the plated layer on the insulating layer, and similarly, exposure, development, and etching are performed, and the photosensitive resist is peeled off to form a circuit on the insulating layer.
Thereafter, if necessary, the plated layer on which the circuit is formed is further subjected to corrosion resistance treatment such as nickel plating, and is cut into a desired shape by punching or the like, whereby an HDD suspension can be obtained.

  The laminate obtained by the HDD suspension manufacturing method of the present invention aims to increase the capacity of the HDD, and facilitates the fine wiring processing of the HDD suspension having multiple lines. In addition, the accuracy of attaching the wiring to the slider to be reduced is increased, and the control of the spring property for adjusting the flying height of the slider of the suspension is facilitated. Furthermore, because pure copper is used, it is possible to improve impedance control, reduce electrical signal loss, and increase transmission speed by increasing the conductivity, and omits subsequent processes such as laser beam irradiation when processing into a suspension. The suspension can be manufactured at a low cost.

  Hereinafter, the present invention will be described more specifically based on examples and comparative examples. In addition, the evaluation method of the basic characteristic in an Example is based on the following method, and the basic performance required for HDD suspension use is described together below. The polyimide resin used as the sample was one that had been sufficiently imidized.

1) Measurement of peel strength: Adhesive strength between metal foil and polyimide resin can be measured by forming a polyimide resin layer on a stainless steel foil, forming a conductor layer by sputtering-plating, and then processing the circuit. A test piece for measuring / 8 inch wiring width was prepared. Affix this sample to the SUS foil side and copper foil side to the fixed plate, and peel off each metal foil in 90 ° direction using a tensile tester (Toyo Seiki Co., Ltd., Strograph-M1) It was measured.

2) Measurement of warpage: For the warpage of the laminate, a disk having a diameter of 65 mm was prepared by circuit processing, and the portion where the warpage was the largest when placed on a desk using a caliper was measured.

3) Measurement of linear thermal expansion coefficient: The linear thermal expansion coefficient is measured at a rate of 20 ° C / min up to 255 ° C using a thermomechanical analyzer (manufactured by Seiko Instruments Inc.), and at that temperature for 10 minutes. After being held, it was further cooled at a constant rate of 5 ° C./min. The average thermal expansion coefficient (linear thermal expansion coefficient) from 240 ° C. to 100 ° C. during cooling was calculated.

Abbreviations used in Examples and the like are as follows.
BPDA: 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride
DADMB: 4,4'-diamino-2,2'-dimethylbiphenyl
BAPP: 2,2-bis [4- (4-aminophenoxy) phenyl] propane
DMAc: N, N-dimethylacetamide

Synthesis example 1
In order to synthesize a low thermal expansion polyimide resin layer with a linear expansion coefficient of 30 × 10 ^-6 / ° C or less, 9.0 mol of DADMB was weighed and stirred in a 40 L planetary mixer to 25.5 kg of solvent DMAc. Dissolved. Next, 8.9 mol of BPDA was added, and the polymerization reaction was continued by stirring at room temperature for 3 hours to obtain a viscous polyimide precursor A solution.

Synthesis example 2
As a polyimide resin layer having a glass transition temperature of 300 ° C. or less, 6.3 mol of DADMB was weighed and dissolved in 25.5 kg of solvent DMAc while stirring in a 40 L planetary mixer. Next, 6.4 mol of BPDA was added, and the polymerization reaction was carried out by continuing stirring at room temperature for 3 hours to obtain a solution of a viscous polyimide precursor B.

The polyimide precursor B solution obtained in Synthesis Example 2 was applied on a stainless steel foil (manufactured by Nippon Steel Corporation, SUS304, tension annealed product, thickness 20 μm) so that the thickness after curing was 1 μm. After drying at 110 ° C. for 3 minutes, the polyimide precursor A solution obtained in Synthesis Example 1 was applied thereon so that the thickness after curing was 7.5 μm, and dried at 110 ° C. for 10 minutes. Furthermore, the polyimide precursor B solution obtained in Synthesis Example 2 was applied thereon so that the thickness after curing was 1.5 μm and dried at 110 ° C. for 3 minutes, and further in the range of 130 to 360 ° C. The imidization was completed by heat treatment in several steps for 3 minutes each to obtain a laminate having a polyimide resin layer thickness of 10 μm on stainless steel.
Next, Cr was sputtered to 3 nm on the polyimide resin surface of the obtained stainless steel / polyimide resin laminate, and Cu was sputtered to 200 nm on the sputtered layer to ensure conductivity. A 12 μm Cu plating layer was formed thereon by electrolytic plating. As a result of evaluating the laminated body thus obtained, a laminated body satisfying the basic performance as a flexure blank as shown in Table 1 and suitable for fine processing was obtained. In addition, the polyimide resin can be processed only by plasma irradiation, and can be processed without any complicated post-process.

A laminate having a polyimide resin layer thickness of 10 μm was formed on stainless steel by the same method as in Example 1.
Next, after sputtering 3 nm of Mo on the polyimide resin surface of the stainless steel / polyimide resin laminate obtained here and further sputtering 200 nm of Cu on the sputtered layer, the electroplating method is used. A 12 μm Cu plating layer was formed. As a result of evaluating the laminate thus obtained, as shown in Table 1, a laminate that satisfies the basic performance as a flexure blank as in Example 1 and is suitable for fine processing was obtained. In addition, the polyimide resin can be processed only by plasma irradiation, and can be processed without any complicated post-process.

Comparative Example 1
A laminate having a polyimide resin layer thickness of 10 μm was formed on stainless steel by the same method as in Example 1.
Next, Cr was sputtered on the polyimide resin surface of the stainless steel / polyimide resin laminate obtained here for 1 nm, and Cu was sputtered on the sputtered layer for 200 nm to ensure conductivity. A 12 μm Cu plating layer was formed. As a result of evaluating the laminated body thus obtained, as shown in Table 1, the peel strength varied, and the required adhesive strength of the suspension could not be satisfied.

Comparative Example 2
A laminate having a polyimide resin layer thickness of 10 μm was formed on stainless steel by the same method as in Example 1.
Next, when Cr was sputtered to 400 nm on the polyimide resin surface of the stainless steel / polyimide resin laminate obtained here, cracks occurred, and furthermore, Cu was sputtered to 200 nm on the sputtered layer to ensure conductivity, Furthermore, when a 12 μm Cu plating layer was formed by electrolytic plating, a stable conductor layer such as the generation of pinholes could not be obtained.

Comparative Example 3
A laminate having a polyimide resin layer thickness of 10 μm was formed on stainless steel by the same method as in Example 1.
Next, Cr was sputtered on the polyimide resin surface of the obtained stainless steel / polyimide resin laminate by 3 nm, and Cu was sputtered on the sputtered layer by 10 nm to ensure conductivity, and further by electrolytic plating. When a 12 μm Cu plating layer was formed, pinholes were generated and a stable conductor layer could not be formed.

Table 1 shows the results of evaluating the laminates of Examples 1 and 2 and Comparative Examples 1 to 3 obtained as described above. The adhesive strength and warpage between stainless steel and polyimide and between conductor layer and polyimide were measured by processing the stainless steel and copper foil into arbitrary shapes using ferric chloride, respectively, and then evaluating with the method described above. did.
When the laminate was subjected to a heat resistance test for 1 hour in an oven at 300 ° C., no abnormality such as swelling and peeling was observed in all systems. The linear thermal expansion coefficient of the polyimide film obtained by etching away the metal foil is as shown in the table below, and almost no warpage was observed in the laminate obtained by etching the metal foil into an arbitrary shape in all systems. There wasn't.

Claims (8)

In the manufacturing method of the HDD suspension laminate comprising the stainless steel layer A, the insulating resin layer B, the seed layer and the plating layer E,
a) On the stainless steel layer A, a polyimide resin solution or a precursor solution thereof is applied, dried and heat-treated to form an insulating resin layer B composed of a plurality of polyimide resin layers. The expansion coefficient is 1 × 10 ^{−5 to} 3 × 10 ⁻⁵ / ° C., and the layers on both sides are polyimide resin layers having a glass transition temperature of 300 ° C. or lower.
b) forming a first seed layer C as a metal thin film on the insulating resin layer B by sputtering;
c) forming a second seed layer D as a metal thin film having better conductivity than the metal thin film of the first seed layer C on the first seed layer C by sputtering;
d) forming a plating layer E to be a conductor layer on the second seed layer D;
The manufacturing method of the laminated body for HDD suspension characterized by including each process of these.   The adhesive strength between the first seed layer C and the second seed layer D and the adhesive strength between the second seed layer D and the plating layer E are both 0.6 kN / m or more. A method for producing a laminate for an HDD suspension as described in 1.   The method for producing a laminate for an HDD suspension according to claim 1 or 2, wherein the first seed layer C is a metal layer made of Cr, Mo, Ni, Ti, Be, Si or an alloy thereof having a thickness of 2 to 10 nm. .   4. The HDD according to claim 1, wherein the second seed layer D is a metal layer having a thickness of 100 to 300 nm, and the first seed layer C is a metal layer having a thickness of 2 to 30 nm. A method for manufacturing a suspension laminate.   5. The HDD suspension laminate according to claim 1, wherein the plating layer E is made of a metal layer made of copper having a thickness of 5 to 15 μm or a copper alloy containing copper as a main component. Method.   6. The method for manufacturing a laminate for an HDD suspension according to claim 1, wherein the insulating resin layer B has a thickness of 5 to 18 [mu] m.   The method for manufacturing a laminate for an HDD suspension according to claim 1, wherein the stainless steel layer A is made of SUS304 having a thickness of 5 to 30 μm. In the HDD suspension manufacturing method,
e) a step of preparing an HDD suspension laminate obtained by the method for manufacturing an HDD suspension laminate according to any one of claims 1 to 7;
f) using the resist as a mask on the surface of the plating layer E, etching the exposed plating layer, removing the resist, and forming a plating layer having a pattern on the insulating resin layer B; and
g) removing unnecessary portions of the insulating resin layer B to form an insulating resin layer having a pattern;
The manufacturing method of the HDD suspension characterized by including each process of these.