Process for the correction of curls of flexible metal clad lamin

Details Process for the correction of curls of flexible metal clad lamin Process for the correction of curls of flexible metal clad lamin

1987-10-27

1988-12-06

Crane, Daniel C.

Metal deforming

By deflecting successively-presented portions of work during...

By use of deflected arranged to provide longitudinally...

72183, 72342, 72 46, 226197, 264285, 493459, 29846, B21D 102, B31F 100, H05K 300

Patent

active

047888466

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

1. Technical Field
This invention relates to a process for the correction of curls of a long flexible metal clad laminate (hereinafter called "FMCL"), which has excellent heat resistance, electrical properties and mechanical properties and comprises a metal clad polyimide film, and for the improvement of its dimensional stability. More specifically, this invention is concerned with a process for effecting continuously the correction of curls occurred in a long adhesiveless flexible metal clad laminate (hereinafter called "A-FMCL"), which has been produced by forming a thin film layer of an aromatic polyimide on a metal foil, and the minimization of size reduction of the thin polyimide layer which size reduction takes place upon etching of the metal foil.
2. Background Art
Flexible metal clad laminates are substrates suitable for use in the fabrication of flexible printed circuits and have found an increasing demand in recent years reflecting the size reduction of packages for enclosing printed circuits therein. Such flexible metal clad laminates have heretofore been produced by bonding a polyimide film on a metal foil by means of an adhesive. These laminates are accompanied by a problem that although the polyimide film has sufficient heat resistance, electrical properties and mechanical properties, these properties of the polyimide film are not fully utilized due to insufficient properties of the adhesive.
Accordingly, it has conventionally been investigated to develop a process for producing A-FMCL in which a thin polyimide film and a metal foil make up directly a laminate without interposition of any adhesive layer. U.S. Pat. No. 3,179,634 and Japanese Patent Laid-Open Nos. 129,862/1974, 190,091/1983 and 190,092/1983 maybe mentioned by way of example. Since these processes are simple by themselves and do not require the provision of an adhesive layer, various properties of a resulting A-FMCL reflect various excellent properties of a polyimide used. It has another merit that the reduction of bonding strength of the polyimide with the metal foil does not take place too much even at elevated temperatures.
A-FMCLs, which have been produced as described above and have no adhesive layer, are however accompanied by a drawback that they develop curls which are very troublesome for the fabrication of circuits. This curling takes place due to a difference in size between a polyimide layer and its associated metal foil, which difference is in turn caused by a volume shrinkage occurring unavoidably on the side of the polyimide layer in the course of production of the laminate. Generally, a laminate has a carpet-like appearance rolled up with its metal foil outside as shown in FIG. 4. The thus-curled laminate is accompanied by a drawback that the size reduction of the polyimide film, which occurs upon etching of the metal foil, is very large, i.e., as large as about 0.3-1.0% (as measured in accordance with the method of IPC FC 240). These curling and size reduction are serious drawbacks of flexible metal clad laminates. These drawbacks render the handling of the laminates inconvenient in the screen printing step, chemical etching steps and the like and also damage the resist layers and cause cutting and short-circuiting of conductive elements, whereby the processing of circuits is rendered difficult.
A variety of improvements has hence been proposed to avoid the occurrence of such curling or to reduce curls occurred so as to obtain flatness free of problems to the formation of circuits and such dimensional stability that the size reduction of a polyimide film is 0.1% or lower.
It is possible to avoid completely the volume shrinkage due to the ring-closing reaction of a polyamide acid, a precursor of polyimide, for example, by cast-coating a metal foil with a solvent-soluble aromatic polyimide. Even if this method is followed, the curling and the size reduction of the polyimide upon etching of the metal foil occur due to evaporation of the solvent and the difference in linear coefficient of expansion betw

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