Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
1998-08-31
2001-06-12
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
Composite
Of metal
C427S388100, C427S493000, C427S510000, C427S520000, C427S556000, C428S209000, C428S473500, C428S901000
Reexamination Certificate
active
06245432
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a circuit substrate, a circuit-formed suspension substrate, and production methods thereof. More specifically, the present invention relates to a circuit substrate having an insulating layer composed of a polyimide resin on a metal foil substrate, a circuit-formed suspension substrate having formed on the circuit substrate a pattern circuit composed of a conductive layer, and production methods of the circuit substrate and circuit-formed suspension substrate.
In a magnetic disk device such as a hard disk device which is used as an external storage device for a computer, etc., for performing magnetic recording or regeneration, it is necessary to relatively run the above-described magnetic disk and a magnetic head, elastically push the magnetic head to the magnetic disk against to an air stream formed thereby, and keep a definite fine interval between the magnetic head and the magnetic disk. A magnetic head supporting means for elastically pushing the magnetic head to the magnetic disk against the air stream as described above is a suspension. The present invention relates to a circuit substrate which can be suitably used for producing such a circuit-formed suspension device, a circuit-formed suspension substrate having formed on such a circuit substrate a circuit composed of a conductive layer by a patterning technique, and the production methods of them.
BACKGROUND OF THE INVENTION
Recently, a circuit substrate comprising a metal foil having formed thereon an insulating layer composed of a polyimide resin has been used as a thin-film multilayer circuit substrate for the purposes of high-density packaging of semiconductors and a high-speed signal treatment. However, since the polyimide resin which is conventionally used as an insulating material has a large coefficient of linear thermal expansion, the circuit substrate is liable to cause cracking on the resin layer and warping and the delamination of the resin layer, and warping.
On the other hand, in computers and storage devices which are peripheral equipments for computers, in addition to the improvement of the capacity, small-sizing and a low cost have been required and with such requirements for a background, in particular, the technique of hard disk drives has been greatly advanced. Also, in the magnetic head, recently the developments of a thin-film magnetic head (TFH) wherein the coil portion is made of a thin film and further a thin film-magnetic resistance composite head (MR) which serves reading and writing and has a greatly large storage capacity have been hurried to a conventional metal in gap (MIG).
However, by a conventional technique of constituting desired wiring by laying a conductive wire on a suspension substrate, the conductive wire gives influences on the elastic modulus of the suspension to cause the fluctuation of the pushing force of the suspension and as the case may be, by the contact with the magnetic disk, the durability of the magnetic disk device is sometimes lowered.
Therefore, recently, a suspension formed by directly forming an electric circuit on a suspension substrate for mounting a magnetic head has been practically used. However, the suspension finally obtained using the conventional circuit substrate having a polyimide resin as an insulating layer also causes insulation failure and warping occur, resulting in performance failure in some cases, since the polyimide resin has a coefficient of linear thermal expansion larger than that of a metal foil substrate.
SUMMARY OF THE INVENTION
The present invention has been made to overcome the above-described problems in the conventional circuit substrate comprising a metal foil having formed thereon an insulating layer composed of a polyimide resin and in the circuit-formed suspension substrate prepared by using the circuit substrate.
Accordingly, one object of the present invention is to provide a circuit substrate wherein a coefficient of linear thermal expansion of the polyimide resin is close to that of various metal foils, and hence cracking does not occur on the resin layer, the resin layer does not separate, and warping scarcely occur.
Another object of the present invention is to provide a circuit-formed suspension substrate using the circuit substrate.
Other objects of the present invention are to provide the production methods of the circuit substrate and circuit-formed suspension substrate
A circuit substrate comprises a metal foil substrate and an insulating layer composed of a polyimide resin formed on the metal foil substrate, wherein the polyimide resin is a polyimide resin obtained by the reaction of
(A) p-phenylene diamine and
(B) acid anhydrides of
(a) 3,4,3′,4′-biphenyltetracarboxylic acid dianhydride and
(b) 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane.
More specifically, the polyimide resin is one obtained by reacting a polyamic acid obtained by the reaction of
(A) p-phenylene diamine and
(B) acid anhydrides of
(a) 3,4,3′,4′-biphenyltetracarboxylic acid dianhydride and
(b) 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane in the presence of a photosensitive agent.
The method of producing a circuit substrate according to the present invention comprises forming a coating film composed of a photosensitive polyimide resin precursor on a metal foil substrate, light-exposing, heating after the light-exposure, developing, imidating the precursor by heating to form a circuit substrate having an insulating layer composed of a polyimide resin, wherein the photosensitive polyimide resin precursor is obtained by compounding a polyamic acid obtained by the reaction of
(A) p-phenylene diamine and
(B) acid anhydrides of
(a) 3,4,3′,4′-biphenyltetracarboxylic acid dianhydride and
(b) 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane with a photosensitive agent.
According to the method described above, by light-exposing the coating film composed of the photosensitive polyimide resin precursor and formed on the metal foil substrate in conformity with a definite pattern, heating the film after light-exposure, developing the film to form the definite pattern composed of the above-described precursor, and finally heating the pattern-formed film at high temperature to form polyimide, the circuit substrate having the patterned insulating layer composed of the polyimide resin can be obtained.
The circuit-formed suspension substrate of the present invention comprises a metal foil substrate, an insulating layer composed of a polyimide resin and formed on the metal foil substrate, and a pattern circuit composed of a conductive layer and formed on the insulating layer, wherein the polyimide resin is a polyimide resin obtained by the reaction of p-phenylene diamine and acid anhydrides of 3,4,3′,4′-biphenyltetracarboxylic acid dianhydride and 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane.
Also, the method of producing a circuit-formed suspension substrate according to the present invention comprises forming a pattern circuit composed of a conductor layer on the insulating layer composed of the polyimide resin of the circuit substrate described above, wherein the photosensitive polyimide resin precursor for forming the insulating layer of the circuit substrate is obtained by compounding the polyamic acid obtained by the reaction of p-phenylene diamine and an acid anhydride of 3,4,3′,4′-biphenyltetracarboxylic acid dianhydride and 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane with a photosensitive agent.
The circuit-formed suspension substrate is obtained by preparing the above-described circuit substrate having the definite-patterned insulating layer composed of the polyimide resin and then forming a pattern-circuit composed of a conductive layer on the insulating layer.
REFERENCES:
patent: 5578697 (1996-11-01), Kawamonzen et al.
patent: 5605763 (1997-02-01), Yusa et al.
patent: 5665802 (1997-09-01), Maki et al.
patent: 5670609 (1997-09-01), Auman et al.
patent: 5849397 (1998-12-01), Kohno et al.
patent: 5858518 (1999-01-01), Omote et al.
Funada Yasuhito
Omote Toshihiko
Nakarani D. S.
Nitro Denko Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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