JP2005285198A - Laminate for hdd suspension and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminate for a suspension superior in flatness using rolled copper foil or electrolytic copper foil having high conductivity and low strength, and a method for manufacturing the same. <P>SOLUTION: The laminate for the HDD suspension is composed of a stainless steel layer, a polyimide resin layer and a conductive layer, wherein the conductive layer is copper foil having a thickness of 1-20 μm, a tensile strength of ≤600 MPa, and a conductivity ratio of ≥90%, and warpage in a 65 mm disk is ≤3 mm. In the method for manufacturing the laminate for the HDD suspension, the laminate composed of the stainless steel layer, the polyimide layer and the conductive layer is made by stacking the rolled copper foil or the electrolytic copper foil on the polyimide resin layer after the polyimide resin layer is formed on the stainless steel layer, and by performing heat crimping at a temperature of ≥280°C. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a laminate used for an HDD suspension and a manufacturing method thereof. Specifically, the present invention relates to a laminate for an HDD suspension having excellent flatness and a method for manufacturing the same.

  The suspension mounted on the hard disk drive (hereinafter referred to as HDD) is a wiring-integrated type that has stable buoyancy and positional accuracy with respect to the disk that is the storage medium, from the wire type suspension that has been conventionally used as the capacity increases. Most have been replaced by suspension. This wiring-integrated suspension is a type in which a flexible printed circuit board called FSA (flex suspension assembly) method is processed and bonded using an adhesive, and a polyimide acid precursor called CIS (circuit integrated suspension) method. After processing the shape, it is imidized and further formed into a wire by forming a wire on the polyimide. A laminated body made of stainless steel foil-polyimide resin-copper foil called TSA (trace suspension assembly) method is predetermined by etching. There are three types of processing.

  Although the FSA method is easy and inexpensive to process, it is said that it cannot be technically supported when the fine wiring is further advanced in the future because the position accuracy in joining with the terminal is poor because it is attached using an adhesive. . In addition, the CIS method has many advantages such as excellent dimensional accuracy because the wiring is formed directly on the polyimide, and the use of pure copper has many advantages such as easy control of electrical characteristics. In the shape processing called lead, imidized polyimide resin has to be removed with a laser or the like, which increases the number of processes, and there are many disadvantages such as high cost. The TSA suspension can be used for a wide range of joining methods, such as easily forming a flying lead by laminating high-strength copper foil and making it easy to connect by ultrasonic bonding used to connect a read / write cable. It is. In addition, it is widely used because of its high degree of freedom in shape processing and relatively low cost and good dimensional accuracy.

  An HDD suspension laminate in which a polyimide resin layer and a conductor layer are sequentially formed on a stainless steel substrate has already been disclosed (see, for example, Patent Document 1). In this document, what defines the linear expansion coefficient of the polyimide resin layer and the adhesive force between the polyimide resin layer and the conductor layer is described in order to obtain a laminate suitable for the HDD suspension laminate. However, with the technology disclosed here alone, it is difficult to cope with impedance control and miniaturization in order to cope with future increases in HDD capacity and data transmission speed.

  Therefore, the Company has already applied for a patent on a laminate for an HDD suspension using a copper foil having high strength and high conductivity (see, for example, Patent Document 2). However, high strength copper foil is required for the ultrasonic bonding method, but high strength is not required for the solder bonding method. In addition, it is required to control the stiffness in order to maintain the flying distance of the HDD disk and the slider and the flying posture of the slider, and in order to control this, the copper foil or insulating resin that inhibits the stiffness control is required. It is preferable that strength and rigidity are low. Furthermore, since the alloy-based rolled copper foil has inferior conductivity to the rolled copper foil or electrolytic copper foil of pure copper, it is difficult to control the impedance for dealing with the increase in data transmission speed.

In order to solve this problem, a laminate material of stainless steel foil / insulating layer / conductor layer system using rolled copper foil or electrolytic copper foil with high conductivity has been desired, but rolled copper foil or electrolytic copper with high conductivity has been desired. When the foil was laminated at a high temperature, there was a problem that warping was likely to occur because the copper foil stretched.
WO98 / 08216 Japanese Patent Application No. 2002-342457

  An object of this invention is to provide the laminated body for suspension excellent in flatness using the rolled copper foil or electrolytic copper foil with high electrical conductivity and low intensity | strength, and its manufacturing method.

As a result of intensive studies to solve such problems, the present inventors have completed the present invention by obtaining optimum manufacturing conditions using a rolled copper foil or electrolytic copper foil having high conductivity and low strength. It came.

  That is, the present invention is composed of a stainless steel layer / polyimide resin layer / conductor layer, a rolled copper foil or an electrolytic copper foil having a tensile strength of 600 MPa or less and a conductivity of 90% or more, and a warpage in a 65 mm disk is 3 mm or less. The laminate for HDD suspension characterized by the above.

  The above-mentioned laminate for an HDD suspension in which the thickness of the stainless steel layer in the present invention is in the range of 5 to 30 μm and the thickness of the polyimide resin layer is in the range of 5 to 20 μm is desirable.

  In the present invention, a polyimide resin solution is applied to a 5-30 μm stainless steel foil or a rolled copper foil or an electrolytic copper foil having a thickness of 1-20 μm, a tensile strength of 600 MPa or less, and an electrical conductivity of 90% or more, and heat-treated to form a polyimide resin layer. After the formation, a rolled copper foil, an electrolytic copper foil or a stainless steel foil having a thickness of 5 to 20 μm, a tensile strength of 600 MPa or less, and an electrical conductivity of 90% or more is superposed on the polyimide resin layer, and thermocompression bonded at a temperature of 280 ° C. It is a manufacturing method of the laminated body for HDD suspension characterized by setting it as the laminated body comprised from a stainless steel layer / polyimide layer / conductor layer.

  According to the present invention, by using a rolled copper foil or electrolytic copper foil having high conductivity and low strength for the conductor layer, there is no warpage and the flying distance of the disk and slider corresponding to the increase in capacity of the HDD is shortened. And a laminate for a HDD suspension substrate that can easily control the stiffness required to stabilize the flying posture of the slider, improve impedance control, reduce electrical signal loss, and improve transmission speed. Can be provided.

  The laminate for HDD suspension of the present invention (hereinafter referred to as a laminate) comprises a stainless layer / polyimide resin layer / conductor layer. The stainless steel layer in the present invention is not particularly limited, but from the viewpoint of spring characteristics and dimensional stability, a high-elasticity and high-strength stainless steel foil such as SUS304 is preferable, and SUS304 annealed at a temperature of 300 ° C. or higher is particularly preferable. preferable. The thickness of the stainless steel used is preferably in the range of 5 to 30 μm, and particularly preferably in the range of 10 to 20 μm.

  If the thickness of the stainless steel layer is less than 5 μm, there is a possibility that the spring property that sufficiently suppresses the flying height of the slider cannot be secured. On the other hand, if the thickness exceeds 30 μm, the rigidity becomes too large and it is difficult to lower the slider mounted. There is a risk.

  The polyimide resin which comprises an insulating layer in the laminated body of this invention should just have an imide bond in the structure, such as a polyimide, a polyamideimide, a polyetherimide. The polyimide resin layer may be composed of only a single layer, but is preferably composed of a plurality of polyimide resin layers. When making a polyimide layer into a polyimide resin layer of multiple layers, it is preferable to use what shows favorable adhesiveness with these conductor layers or stainless steel layers for the polyimide resin layer which touches a conductor layer or stainless steel layer.

Examples of the polyimide resin exhibiting good adhesion include those having a glass transition temperature of 300 ° C. or lower. In addition, the intermediate layer not in contact with the conductor layer or the stainless steel 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 from the viewpoint of dimensional stability when HDD suspension is used. Is preferably used. When forming a polyimide resin layer with 3 or more layers, the thickness (t _b) ratio of the total thickness of the both outermost layers (t _a) and the other intermediate layer, t _a / t _b = 0.1~ A range of 0.5 is advantageous.

  The conductor layer in the present invention is formed from a rolled copper foil or an electrolytic copper foil having high conductivity. The thickness of the rolled copper foil or the electrolytic copper foil forming the conductor layer needs to be 1 to 20 μm, and preferably 3 to 18 μm. There is no particular limitation on the point where the thickness is less than 3 μm. However, if the thickness is less than 3 μm, the handling property is deteriorated, and problems such as a decrease in yield occur. On the other hand, if it exceeds 18 μm, the strength of the copper foil has a great influence on the stiffness control for controlling the flying of the slider, and it becomes difficult to process into fine wiring.

  Moreover, regarding the thickness of the copper foil used in the present invention, a commercially available copper foil may be used, but it may be later processed to a predetermined thickness using a half etching method or the like. The conductor layer used in the present invention preferably has a conductivity of 90% or more. When less than 90%, it becomes difficult to control the impedance corresponding to the increase in data transfer speed.

  Moreover, it is preferable that the tensile strength of the conductor layer used by this invention is 600 Mpa or less. Exceeding 600 MPa is not preferable because it adversely affects the strict stiffness control required for HDD suspensions. The lower limit is preferably closer to 0, but practically 200 MPa or more.

Next, the manufacturing method of the laminated body of this invention is demonstrated.
When manufacturing a laminated body, first, a polyimide resin liquid is apply | coated on 5-30 micrometers stainless steel foil used as a base | substrate. The polyimide resin liquid 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 resin solution is used, and after application, the solvent is removed to some extent by preheating. A method of imidization by heat treatment after removal is preferred. In addition, when using the imidized polyimide resin solution, the heat processing for imidation is naturally omitted.

  Thus, when the polyimide resin layer is formed, a rolled copper foil or an electrolytic copper foil having a thickness of 1 to 20 μm, a tensile strength of 600 MPa or less, and a conductivity of 90% or more, which is a conductor layer, is superposed at a temperature of 280 ° C. or more. , Pressurize in the range of 3 to 120 minutes. When the pressurization time exceeds 120 minutes, warpage is likely to occur due to heat elongation of the copper foil, and it is difficult to obtain a stable laminate material. Further, when the pressurization time is less than 3 minutes, a sufficient peel strength cannot be obtained, which is not preferable. A more preferable heating and pressing time is 10 to 100 minutes. Moreover, there is no problem even if a polyimide resin layer is formed on a rolled copper foil or an electrolytic copper foil to be a conductor layer, and a stainless steel foil is overlapped later.

Hereinafter, the present invention will be described more specifically based on examples and comparative examples.
The evaluation of various characteristics in the examples is based on the following method. Moreover, the polyimide used as a sample was sufficiently imidized.

(A) Measurement of peel strength The adhesive strength between the metal foil and the polyimide resin is such that after forming a polyimide resin layer on the stainless steel foil, the copper foil is further thermocompression bonded to create a laminate of double-sided metal foil. Then, a test piece for measuring 1/8 inch wiring width was prepared by circuit processing. Affix the SUS foil side and the copper foil side to the fixed plate, and peel off each metal foil in the 90 ° direction using a tensile tester (Toyo Seiki Co., Ltd., Strograph-M1). It was measured.

(B) Measurement of warpage As for the warpage of the laminated body, a distance between a portion having the largest warpage and a desk surface was measured when a disk having a diameter of 65 mm was prepared by circuit processing and placed on a desk using a caliper.

(C) Conductivity measurement After degreasing the copper foil with acetone, the roughened portion was dropped with a soft etching solution consisting of a mixed acid of 10% sulfuric acid and 5% hydrogen peroxide, and then a strip 300 mm long x 10 mm wide. The test piece was cut out, and the conductivity was measured in a constant temperature room at 20 ° C. using a precision low voltage current potentiometer manufactured by Yokogawa Hokushin Electric Co., Ltd.

(D) Measurement of strength of copper foil A strip-shaped test piece having a width of 12.7 mm and a length of 254 mm was cut out, and the crosshead speed was 50 mm / min using a tensile testing machine (Toyo Seiki Co., Ltd., Strograph-R1). The distance between chucks was 50.8 mm, the displacement (elongation) during the tensile test was determined, and the 0.2% yield strength was calculated from the SS curve.

(E) Measurement of linear thermal expansion coefficient The linear thermal expansion coefficient was measured at a rate of 20 ° C./minute 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-amino Phenoxy) phenyl] propane DMAc: N, N-dimethylacetamide

Synthesis example 1
In order to synthesize a low thermal expansion polyimide resin layer having a linear expansion coefficient of 30 × 10 ⁻⁶ / ° C. or lower, 9.0 mol of DADMB was weighed and stirred in a 40 L planetary mixer with the solvent DMAc 25. Dissolved in 5 kg. 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 the solvent DMAc while stirring in a 40 L planetary mixer. Next, 6.4 mol of BPDA was added, and the polymerization reaction was continued for 3 hours at room temperature to obtain a viscous polyimide precursor B solution.

Example 1
The solution of polyimide precursor B obtained in Synthesis Example 2 was applied on a stainless steel foil (manufactured by Nippon Steel Corp., 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. Further, 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 then further 130 to 360 ° C. In several steps, imidization was completed by stepwise heat treatment for 3 minutes each for 3 minutes to obtain a laminate having a polyimide resin layer thickness of 10 μm on stainless steel. The first polyimide resin layer and the third polyimide resin layer were the same. Next, copper foil (USLP, copper foil thickness 12 μm) made by Nihon Electrolytic Co., Ltd. is laminated, and the desired laminate is subjected to thermocompression bonding using a vacuum press machine under conditions of a surface pressure of 10 MPa, a temperature of 300 ° C., and a press time of 20 minutes. Got. This laminated body sufficiently satisfies the basic performance required as a suspension substrate material such as tensile strength and warpage, and has led to obtaining a material having high conductivity. The results are shown in Table 1 together with the physical properties of the copper foil used.

Example 2
By a method similar to that of Example 1, a laminate having a polyimide resin layer thickness of 10 μm was formed on Nippon Electrolytic copper foil (USLP, copper foil thickness 12 μm). Next, stainless steel was overlaid, and a target laminate was obtained by thermocompression bonding under conditions of a surface pressure of 10 MPa, a temperature of 300 ° C., and a press time of 20 minutes using a vacuum press. The results of evaluating the properties of this laminate are shown in Table 1.

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, an electrolytic foil made of Mitsui Metal (NA-VLP, copper foil thickness 12 μm) is overlaid and heat-pressed using a vacuum press machine under conditions of a surface pressure of 10 Mpa, a temperature of 300 ° C., and a press time of 60 minutes. A laminate was obtained. The results of evaluating the properties of this laminate are shown in Table 1.

Comparative Example 1
In the same manner as in Example 1, a laminate having a polyimide resin layer thickness of 10 μm was formed on stainless steel. Next, a copper foil made of Nihon Electrolytic (USLP, copper foil thickness 12 μm) is superposed and heat-pressed using a vacuum press machine under conditions of a surface pressure of 10 MPa, a temperature of 300 ° C., and a press time of 150 minutes. Got. As shown in Table 1, as a result of evaluating the characteristics of the laminate, it was confirmed that warpage is large and is not suitable as a suspension board material.

Claims (6)

  It is composed of a stainless steel layer / polyimide resin layer / conductor layer, and the conductor layer is a rolled copper foil or electrolytic copper foil having a thickness of 1 to 20 μm, a tensile strength of 600 MPa or less, and an electrical conductivity of 90% or more, and warpage in a 65 mm disk is 3 mm or less. A laminate for HDD suspension, characterized in that   The laminate for an HDD suspension according to claim 1, wherein the stainless steel layer has a thickness in the range of 5 to 30 μm.   The suspension laminate according to claim 1 or 2, wherein the polyimide resin layer has a thickness in the range of 5 to 20 µm.   After forming a polyimide resin layer on the stainless steel layer, a rolled copper foil or an electrolytic copper foil having a thickness of 1 to 20 μm, a tensile strength of 600 MPa or less, and a conductivity of 90% or more is superposed on the polyimide resin layer at a temperature of 280 ° C. or more. A method for producing a laminate for an HDD suspension, wherein the laminate is made of a stainless steel layer / polyimide layer / conductor layer by thermocompression bonding.   After forming a polyimide resin layer on a rolled copper foil or electrolytic copper foil having a thickness of 1 to 20 μm, a tensile strength of 600 MPa or less, and an electrical conductivity of 90% or more, a stainless steel foil is overlaid on the polyimide resin layer, and a temperature of 280 ° C. or more. A method of manufacturing a laminate for an HDD suspension, wherein the laminate is made of a stainless steel layer / polyimide layer / conductor layer by thermocompression bonding. 6. The method for manufacturing a laminate for an HDD suspension according to claim 5, wherein the heating and pressing time at 280 [deg.] C. or higher is in the range of 3 to 120 minutes.