Stock material or miscellaneous articles – Composite – Of metal
Patent
1992-04-29
1994-04-05
Thibodeau, Paul J.
Stock material or miscellaneous articles
Composite
Of metal
428209, 428457, B32B 1508, H05K 103, H05K 330, H05K 338
Patent
active
053003640
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a polyimide flexible metal-clad laminate having no adhesive and a method for producing the same. More specifically, it relates to a method for producing a printed circuit board by the use of the above-mentioned metal-clad laminate and an electronic device in which electronic parts are mounted on the printed circuit board.
BACKGROUND ART
When a flexible metal-clad laminate (hereinafter referred to as "flexible metal-clad laminate") is etched to remove unnecessary portions of a conductive material from the board, a printed circuit board can be formed. On this printed circuit board, various electronic parts such as semiconductors are mounted, and the board is then incorporated into an electronic apparatus.
The mounting is to attach parts to the board by the use of soldering, screwing or the employment of wiring materials. Examples of the mounting means include parts insertion type mounting, surface mounting, flexible mounting, tip bonding mounting, controlled collapse bonding mounting and organic multitip mounting.
In recent years, the mounting density of the parts on this kind of printed printed circuit boards has increased year by year, and there is the tendency that the mounting means be automated. In these mounting steps, the automatic soldering is carried out at a high temperature, and therefore the boards are required to be heat-resistant.
Furthermore, in the step of circuit formation, a chemical or thermal change such as etching or washing is given, but it is required in this step that the board maintains an original plane state without curling and without separation between the metallic conductor and film used.
Each of the conventional polyimide flexible metal-clad laminates is mainly formed by causing a polyimide film to adhere to a metallic conductive foil with the interposition of an adhesive. However, since this laminate contains the adhesive, its heat resistance is poor and its electrical properties change with time, and therefore it is difficult to apply conventional boards to a field in which the high-density circuits are automatically mounted on the laminates.
As means for solving these problems, methods for producing a polyimide flexible metal-clad laminate having no adhesive have been disclosed in which there is directly applied, to a metallic conductive foil, a solution of a polyimide precursor having a linear thermal expansion coefficient substantially equal to that of the metallic conductive foil, followed by a thermal cure treatment to form a polyimide film thereon (Japanese Patent Application Laid-open Nos. 61-111359, 63-214185, 58-155790, 63-245988 and 61-111182).
The polyimide flexible metal-clad laminate having no adhesive not only solves the problem of deterioration by the adhesive but also permits the remarkable simplification of a manufacturing process and the decrease of cost. However, in order to prepare this polyimide flexible metal-clad laminate having no adhesive, it is necessary to select the polyimide having a linear thermal expansion coefficient substantially equal to that of the conductor, considering the curl properties of the laminate.
Nevertheless, the thus obtained flexible metal-clad laminate curls immediately after the curing, with the conductor foil facing to the outside. In addition, when the unnecessary portions of the conductor are removed by etching to form a circuit, the polyimide film curls, with the conductor foil facing to the inside, which interferes with the subsequent operation.
As a technique for controlling the curl immediately after the curing, Japanese Patent Application Laid-open Nos. 59-22388 and 59-22389 have disclosed a simple curl prevention method by which a reverse bending plastic deformation is given to the metal. In the case of this method, stress must be forcedly applied to the metal conductor, and thus the metal conductor is fatigued.
In addition, another method for preventing the board from curling has been disclosed in which the laminate is bent in a drying/curing step for the formatio
REFERENCES:
patent: 4778872 (1988-10-01), Sasaki et al.
patent: 4937133 (1990-06-01), Watanabe et al.
patent: 4939039 (1990-06-01), Watanabe
patent: 5112694 (1992-05-01), Konotsune et al.
Hase Hiroaki
Kikuta Kazutsune
Konotsune Shiro
Takahashi Atsushi
Chisso Corporation
Nakarani D. S.
Thibodeau Paul J.
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