Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Patent
1980-02-05
1982-10-12
Robinson, Ellis P.
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
428213, 428215, 428209, 428411, 428418, 428458, 4284735, 4284744, 428901, 427 96, 427386, 4273881, 4273882, 174 685, H05K 100, B32B 1508, B32B 2734, B32B 2738
Patent
active
043539548
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a heat-resistant flexible printed circuit base board produced by forming an electrically insulating coating directly on a metal foil without using any electrically insulating film or a fibrous base material, and to a method for producing the same.
BACKGROUND ART
Increasing requirements are seen recently for simplification of the mounting system, miniaturization, high reliability and high performance of the communication appliances, domestic appliances, electronic computers, and sounding devices, and similar requirements are made of the printed circuit boards incorporated in such appliances.
Among printed circuit boards, flexible printed circuit boards can meet these requirements as they are light in weight, compact in structure, and capable of bending and three-dimensional wiring, and they are recently, therefore, prevalently used as printed circuit boards for a variety of appliances.
As such flexible printed circuit base boards, there have been used the so-called flexible copper-clad laminates obtained by bonding an electrically insulating film such as polyester resin film, polyimide resin film, fluorocarbon resin film, etc., to a copper foil through an adhesive or by bonding to a copper foil a prepreg prepared by impregnating a fibrous base material such as glass cloth, glass non-woven fabric or the like with a heat-resistant resin, such as epoxy resin or the like. However, in the case of bonding an electrically insulating film to a metal foil through an adhesive, the product quality is greatly affected by not only the properties of the film per se but also the properties of the adhesive used, and particularly in the case where the product is based on a film excellent in heat-resistance and dimensional stability, such as polyimide film, the innate properties of the film such as heat-resistance and the like, are attenuated by the adhesive and not utilized to produce the best effect. On the other hand, the copper-clad laminate in which the fibrous base material is used is insufficient in flexibility, such as folding endurance, and often breaks when used in three-dimensional wiring as a printed circuit board, whereby troubles are often caused. There is also known a method of bonding a plastic film, a resin powder or the like to a metal foil by melt-adhesion without using any adhesive, but the films or powders with high heat-resistance have themselves a high melting point and are hard to melt-adhere, so that there are many limitations, such as a specific treatment or a very high temperature pressing equipment is required. Therefore, it is not easy and is very costly to carry out said method on an industrial scale.
On the other hand, when an electric insulating resin is coated in a wet state on the surface of a metal foil and dried to form a coating, and the thus obtained coating per se is used as an electric insulating layer and a support for a flexible printed circuit, the resulting laminate has various advantages as mentioned below as compared with the above-mentioned conventional materials and becomes a very commercially attractive laminate:
(1) Because of use of no adhesive, the properties of the resin per se are retained in their entirety in printed circuit boards.
(2) It becomes unnecessary to subject a film along with a metal foil to pressing step, and hence, the productivity is increased.
(3) The control of the thickness of the coating as an insulating layer and a support can freely be effected to enable the manufacture of a very thin base board.
(4) Continuous production is facilitated. A solution casting method is known for the formation of such a coating, and a varnish of a resin, such as epoxy resin, urethane resin, alkyd resin or the like is known to be able to form a coating on a metal foil by coating the varnish on the metal foil and drying the same.
However, when such a resin is used in the production of a flexible printed circuit base board for the above-mentioned purpose, the following disadvantages are seen:
(1) The coating obtained by applicat
REFERENCES:
patent: 3932689 (1976-01-01), Watanabe
patent: 3985928 (1976-10-01), Watanabe
patent: 4059550 (1977-11-01), Shimp
patent: 4118535 (1978-10-01), Banucci
patent: 4226913 (1980-10-01), Henderson
Endo Toshinaga
Kusuhara Akinobu
Yamaoka Sigenori
Flocks Karl W.
Neimark Sheridan
Robinson Ellis P.
Sumitomo Bakelite Company Limited
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