Stock material or miscellaneous articles – Composite – Of polyimide
Reexamination Certificate
2001-10-02
2003-04-15
Hampton-Hightower, P. (Department: 1711)
Stock material or miscellaneous articles
Composite
Of polyimide
C428S035700, C428S035800, C428S035900, C428S036700, C428S036910, C428S213000, C428S214000, C428S215000, C428S216000, C428S357000, C428S411100, C428S458000
Reexamination Certificate
active
06548180
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims priority of Japanese Application Nos. 2000-302087 filed Oct. 2, 2000 and 2001-230272 filed Jul. 30, 2001, the complete disclosure of which are hereby incorporated by reference.
FIELD OF THE INVENTION
This invention relates to an aromatic polyimide film and further relates to an aromatic polyimide film laminate.
BACKGROUND OF THE INVENTION
Aromatic polyimide films show good high thermal resistance, good chemical properties, high electrical insulating property, and high mechanical strength, and therefore are widely employed in various technical fields. Particularly, an aromatic polyimide film made of polyimide comprising a 3,3′,4,4 ′-biphenyltetracarboxlic acid component and a p-phenylenediamine component (hereinafter referred to as “BPDA-PPD polyimide film”) shows prominently high resistance to heat treatment and chemical processing and further shows a high modulus of tensile elasticity.
Accordingly, the BPDA-PPD polyimide film is very favorably employable in the form of a continuous aromatic polyimide film/metal film composite sheet for manufacturing a flexible printed circuit board (FPC), a carrier tape for tape-automated-bonding (TAB), and a tape of lead-on-chip (LOC) structure.
Previously, a BPDA-PPD polyimide film for the use of manufacturing a carrier tape for TAB or others generally is a relatively thick film such as a film of 75 &mgr;m thick or 125 &mgr;m thick. Recently, however, a demand for utilizing a BPDA-PPD polyimide film having less thickness such as a thickness of less than 55 &mgr;m has increased to respond to requirements for manufacturing more compact electric elements and also for lowering the production cost.
A BPDA-PPD polyimide film having a less thickness such as a thickness of less than 55 &mgr;m can be prepared in the same manner as that employed for the preparation of a BPDA-PPD polyimide film having a thickness of 75 &mgr;m thick or 125 &mgr;m thick. It is assumed that the relatively thin BPDA-PPD polyimide film shows physical characteristics as high as those of the relatively thick BPDA-PPD polyimide film, so long as the same starting materials in the same ratio are employed. However, it has already been found that the thin BPDA-PPD polyimide film shows a less linear expansion coefficient as compared with that of the thick BPDA-PPD polyimide film. The reason is considered as follows:
An aromatic polyimide film is prepared by casting a dope of polyamic acid (i.e., a precursor of polyimide in a solvent) on a continuous belt support, heating the cast dope to give a self-supporting dope film having a less amount of a solvent, separating the dope film from the belt, and heating the dope film to a high temperature such as a temperature in the range of 300 to 550° C. In the step of casting a polyamic acid dope on a continuous belt support, polyamic acid molecules in its surface layer are oriented on the surface of the belt support. The orientation of the polymer molecules in the surface layer is considered to decrease of the linear expansion coefficient of the produced polyimide film. The orientation of the polymer molecules on the surface layer does not give noticeable effect to decrease the linear expansion coefficient of the polyimide film, so long at the film has a relatively large thickness. However, if the polyimide film is a thin film, the orientation of polymer molecules on the surface layer gives noticeable effect to decrease the linear expansion coefficient of the polyimide film.
It is known that an electrolytic copper foil, namely, a representative metal film, has a linear expansion coefficient of approximately 17×10
−6
cm/cm/° C. (in the temperature range of 50-200° C.) in its traverse direction (TD), while an aromatic polyimide film having a thickness of 75 &mgr;m or 125 &mgr;m has a linear expansion coefficient of approximately 20×10
−6
cm/cm/° C. (TD, in the temperature range of 50-200° C.). Accordingly, when a copper film is bonded to the thick aromatic polyimide film with or without a heat-resistant adhesive at a temperature of approximately 150 to 180° C., the produced copper film/polyimide film laminate shows a small curl in such manner that the copper foil takes an outer position, while the polyimide film takes an inner position after the bonded laminate is cooled to room temperature.
In contrast, an aromatic polyimide film having a thickness of less than 55 &mgr;m which is produced in the same manner as that for the producing the thick aromatic polyimide film generally has a linear expansion coefficient of less than 16×10
−6
cm/cm/° C. (TD, in the temperature range of 50-200° C.). Accordingly, when a copper film is bonded to the thin aromatic polyimide film with or without a heat-resistant adhesive at a temperature of approximately 150 to 180° C., the produced copper film/polyimide film laminate shows a noticeable curl in such manner that the copper foil takes an Inner position, while the polyimide film takes an outer position after the bonded laminate is cooled to room temperature. The curl of this type is industrially troublesome and should be avoided.
Until now, a variety of trials for improving physical characteristics of BPDA-PPD polyimide have been disclosed.
Japanese Patent Provisional Publication No. 61-2604027 describes that a polyimide film produced from biphenyltetracarboxylic dianhydride and p-phenylenediamine is heated under application of low tension to give a polyimide film having an increased dimensional stability.
Japanese Patent Publication No. H4-6213 discloses a dimensionally stable polyimide film having a linear expansion coefficient ratio (MD/TD) in a specific range and also having a linear expansion coefficient (MD) in a specific range.
Japanese Patent Publications No. 62-60416, No. 63-5421, and No. 63-5422 describe improvements of releasing easiness of an aromatic polyamic acid film in the dope casting stage.
Japanese Patent Publication No. H3-20130 describes a polyimide film comprising three or four components derived from biphenyltetracarboxylic acid or its derivative, pyromellitic acid or its derivative, phenylenediamine and/or diaminodiphenyl ether.
Japanese Patent Provisional Publications No. 4-198229 and No. 4-339835 disclose a process utilizing a substituted or unsubstituted nitrogen-containing heterocyclic compound.
These known technologies developed for improving certain physical characteristics, however, cannot produce a BPDA-PPD polyimide film having a thickness of 35 to 55 &mgr;m and having an appropriately large linear expansion coefficient.
A thin polyimide film having a thickness of 35 to 55 &mgr;m and having an appropriately large linear expansion coefficient is already known, so long as the polyimide film is produced from a combination other than the combination of 3,3′,4,4′-biphenyltetracarboxylic acid or its reactive derivative and p-phenylenediamine. However, the polyimide film comprising a different combination shows relatively low thermal resistance and modulus of tensile elasticity.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a BPDA-PPD polyimide film having a small thickness such as a thickness of 35 to 55 &mgr;m, an appropriately high linear expansion coefficient and a satisfactory modules of tensile elasticity, and further having a surface on which different material such as adhesive is easily bonded.
It is another object of the invention to provide a metal film/polyimide film laminate having satisfactory physical characteristics and a large bonding force between the metal film and the polyimide film, and having no curl or a small curl in such manner that the metal film takes an inner position, while the polyimide film takes an outer position.
The present invention resides in an aromatic polyimide film of polyimide comprising a 3,3′,4,4′-biphenyltetracarboxylic acid component and a p-phenylenediamine component, which has a thickness of 35 to 55 &mgr;m, a linear thermal expansion coefficient of 17×10
−6
Komoda Norihisa
Mitsui Hiroto
Narui Kohji
Takahashi Takuji
Yamamoto Tomohiko
Hampton-Hightower P.
Reed Smith LLP
Ube Industries Ltd.
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