Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Reexamination Certificate
1999-09-29
2001-06-26
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
C428S213000, C428S214000, C428S216000, C428S458000, C428S473500
Reexamination Certificate
active
06251507
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates a flexible aromatic polyimide film/metal film comsosite sheet.
BACKGROUND OF THE INVENTION
Aromatic polyimide films show a high temperature resistance, a good chemical properties, a high electrical insulating property, and a high mechanical strength, and are widely employed in various technical fields. For instance, an aromatic polyiraide film is favorably employed 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.
The aromatic polyimide film/metal film composite sheet can be produced by bonding a polyimide film and a metal film using a conventional adhesive such as an epoxy resin. However, due to low heat-resistance of the conventional adhesive, the produced composite sheet cannot show a satisfactory heat-resistance.
For obviating the above-mentioned problem, a variety of bonding methods have been proposed. For instance, an aromatic polyimide film/metal film composite sheet is manufactured by forming a copper metal film on an aromatic polyimide film by electroplating. An aromatic polyimide solution (i.e, a solution of a precursor of the aromatic polyimide resin) is coated on a copper film, dried, and heated for producing a polyimide layer on the copper film.
An aromatic polyimide film/metal film composite sheet can be produced using a thermoplastic polyimide resin.
U.S. Pat. No. 4,543,295 describes a polyimide laminate which is produced by applying a pressure onto a composite sheet of an aromatic polyimide film, a polyimide adhesive, and a metal film in vacuo.
It is a problem in the known aromatic polyimide film/metal film composite sheet that a continuous composite sheet is hardly manufactured.
Japanese Patent Provisional Publications No. H4-33847 and No. H4-33848 disclose an aromatic polyimide film/metal film composite sheet manufactured by means of a roll press, which may produce a continuous composite sheet.
According to studies of the present inventors, the roll press is hardly employable for producing a continuous composite sheet having a large width. Moreover, creases or rumples are sometimes observed on the produced composite sheet.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an aromatic polyimide film/metal film composite sheet in which the aromatic polyimide film and the metal film are bonded to each other at a high bonding strength and which has good appearance.
It is another object of the invention to provide a continuous aromatic polyimide film/metal film composite sheet having a large width (such as 400 mm or more), namely in the form of a continuous web, in which the aromatic polyimide film and the metal film are bonded to each other at a high bonding strength and which has good appearance.
It is a further object of the invention to provide an aromatic polyimide film/metal film composite sheet which is favorably employed for manufacturing FPC, TAB tape, or LOC tape.
The present invention resides in a flexible aromatic polyimide film/metal film composite sheet comprising a multi-layered polyimide film comprising a highly heat-resistant aromatic polyimide layer to one surface of which is bonded another aromatic polyimide layer, said multi-layer polyimide film being prepared by simultaneous casting, and a metal film which is bonded to the latter polyimide layer by heating under pressure and subsequent cooling under pressure using a double belt press.
A representative double belt press is described in U.S. Pat. No. 4,599,128, and is commercially available from Held Corporation (Germany).
The aromatic polyimide film/metal film composite sheet of the invention preferably is in the form of a continuous web which preferably has a width of 400 mm or more.
The multi-layered polyimide film of the aromatic polyimide film/metal film composite sheet may further comprise an aromatic polyimide layer which is bonded to another surface of the highly heat-resistant aromatic polyimide layer. To this polyimide layer can be bonded another metal film by heating under pressure using a double belt press.
The simultaneous casting is preferably performed by simultaneously casting a solution containing a precursor of the highly heat-resistant aromatic polyimide in a solvent and a solution containing another aromatic polyimide or its precursor in a solvent on a temporary support.
In the aromatic polyimide film/metal film composite sheet, the highly heat-resistant aromatic polyimide layer preferably has a thickness of 5 to 125 &mgr;m and another aromatic polyimide layer (which is easily bonded to the metal film by applying heat under pressure) preferably has a thickness of 2 to 30 &mgr;m. The metal film preferably is an electrolytic copper film, a rolled copper film, an aluminum film, or a stainless film which preferably has a thickness of 5 to 50 &mgr;m.
The composite sheet of the invention, which has a 90° peel strength of 0.7 kg/cm or more. The peeling may be observed at an interface between the metal film and the polyimide layer.
DETAILED DESCRIPTION OF THE INVENTION
In the invention, the highly heat-resistant aromatic polyimide layer preferably comprises an aromatic polyimide which is preferably prepared by a reaction between 3,3′,4,4′-biphenyltetracarboxylic dianhydride (herein referred to as s-BPDA) and p-phenylenediamine (herein referred to as PPD). If desired, 4,4′-diaminodiphenyl ether (herein referred to as DADE) and/or pyromellitic dianhydride (herein referred to as PMDA) may be employed in combination with s-BPDA and PPD, in molar ratios of 100/0 to 85/15 for PPD/DADE and 100/0 to 50/50 for s-BPDA/PMDA. Alternatively, the aromatic polyimide can be prepared by a reaction between PMDA and a combination of PPD and DADE, in which DADE/PPD is 90/10 to 10/90 in terms of molar ratio. Alternatively, the aromatic polyimide can be prepared by a reaction between a combination of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (herein referred to as BTDA) and PMDA and a combination of PPD and DADE, in which BTDA/PMDA is 20/80 to 90/10 in terms of molar ratio and PPD/DADE is 30/70 to 90/10 in terms of molar ratio.
The highly heat-resistant aromatic polyimide layer preferably has no glass transition temperature at temperatures lower than 350° C., and preferably has a linear expansion coefficient (for both MD and TD directions measured at 50 to 200° C.) in the range of 5×10
−6
to 20×10
−6
cm/cm/° C.
The highly heat-resistant aromatic polyimide can be prepared by random polymerization or block polymerization. Otherwise, previously prepared two or more kinds of polyamide acid solutions are mixed and then subjected to copolymerization to give a highly heat-resistant aromatic polyimide.
The reaction is generally performed in an organic solvent, using the diamine compound(s) and tetracarboxylic dianhydride(s) in equimolar amounts to give a polyamide acid solution, in which a partially imidized polyamide acid may be present. In performing the reaction for preparing a polyamide acid, other aromatic tetracarboxylic diarhydrides and/or other aromatic diatnines such as 4,4′-diaminodiphenylmethane way be employed in combination, provided that the employment of such additional compounds does not essentially vary the desired property of the highly heat-resistant aromatic polyimide. Moreover, the aforementioned aromatic tetracarboxylic dianhydride and aromatic diamine way have on their aromatic rings one or more substituents such as a fluorine atom, hydroxyl, methyl or methoxy.
The aromatic polyimide layer which is thermoplastic and is bonded to the highly heat-resistant aromatic polyimide layer and to which a metal film is bonded preferably comprises an aromatic polyimide which is prepared from a combination of 1,3-bis(4-aminophenoxy)benzene (herein referred to as TPER) and 2,3,3′,4′-biphenyltetracarboxylic dianhydride (herein referred to as a-BPDA), a combination of 1,3-bis(4-
Hosoma Toshinori
Yamamoto Tomohiko
Yoshioka Kazuhiko
Nakarani D. S.
Reed Smith LLP
Ube Industries Ltd.
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