Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2000-07-12
2001-08-07
Lam, Cathy (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C156S090000, C156S286000, C156S289000, C156S293000, C156S323000
Reexamination Certificate
active
06270879
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a release member for use in the production of multi-layer printed wiring boards.
The present application is based on Japanese Patent Application No. Hei. 11-199138, which is incorporated herein by reference.
2. Description of the Related Art
Multi-layer printed wiring boards are manufactured by first laminating wiring boards with prepregs and other hot melt adhesive sheets being interposed and then pressing them under heat so that they are made integral by the adhesive sheets. If the wiring boards to be laminated have holes, part of the molten adhesive sheet will get into the holes to cause a certain inconvenience such as closure.
FIGS. 4A
to
4
C show steps in a conventional process for manufacturing a multi-layer printed wiring board. As shown in
FIG. 4A
, a copper foil
1
″ fitted with an adhesive film
13
′ and having a hole
14
′ is made integral with a wiring board
1
′ by bonding with the adhesive film
13
′. Then, as shown in
FIG. 4C
, a predetermined conductor pattern is formed in the copper foil
1
″ and electrical continuity is established between the conductor pattern and an internal conductor line a′ in the wiring board by means of copper plate b′. A problem with this process is that on account of the pressure and heat applied to make the copper foil integral with the wiring board, part of the molten adhesive film
13
′ sometimes gets into the hole
14
′ to break the conductor path.
In order to deal with this situation, it has been proposed that the perforated copper foil with an adhesive film be overlaid with a release member F′ which, as shown in
FIG. 4B
, consists of a stripping film A′ such as a fluoroplastic film, a thermoplastic resin layer C′ such as a polyethylene layer, and a stripping film B′; when pressed under heating, the thermoplastic resin layer C′ deforms to fill the hole
14
′ with the lower stripping film A′ being at the bottom, thereby preventing the molten adhesive
13
′ from flowing into the hole
14
′.
As the thermoplastic resin layer C′ deforms, the lower stripping film A′ develops resistance but this is extremely small since the depth of the hole
14
′ in the copper foil
1
″ is so small (10-50 &mgr;m) that the strain (elongation) of the film A′ is virtually zero.
However, if the hole is several thousand micrometers deep, the release member has such a great resistance that the lower stripping film works very effectively to prevent the molten thermoplastic resin to flow into the hole, making it difficult for the resin to realize complete closure of the hole; as a result, complete prevention of the adhesive from getting into the hole becomes practically impossible.
Therefore, the conventional release member has been unsuitable for use in laminating an increased number of wiring boards and making them integral to produce a multi-layer printing wiring board having a deep IC chip accommodating cavity as shown in FIG.
2
.
Another difficulty with the conventional release member is that gas evolves from the stripping film in contact with the side where holes are open, potentially causing a practical problem depending upon the structure of the multi-layer printed wiring board.
SUMMARY OF THE INVENTION
An object, therefore, of the present invention is to provide an improved release member for use in producing a multi-layer printed wiring board as a laminate by a process in which a plurality of substrates having internal conductor lines formed therein are laminated with a hot melt adhesive applied therebetween and the laminate in which the surface of the edge of each substrate adjacent a hole through the laminate serves as a wire bonding pad is heated under pressure so that the individual substrates are made integral by bonding with said hot melt adhesive. The release member can positively prevent the adhesive from getting into the hole even if it is very deep.
The stated object of the invention can be attained by a release member for use in producing a multi-layer printed wiring board as a laminate by a process in which a plurality of substrates having internal conductor lines formed therein are laminated with a hot melt adhesive applied therebetween and the laminate in which the surface of the edge of each substrate adjacent a hole through the laminate serves as a wire bonding pad is heated under pressure so that the individual substrates are made integral by bonding with said hot melt adhesive, said release member having a thermoplastic layer sandwiched between stripping films A and B such that it flows toward said hole upon melting when it is heated under pressure, the stripping film A in contact with said laminate having a breaking elongation of no less than 600% and a 100% elongation load of no more than 350 gf per unit width of 1 cm at the temperature to which said laminate is heated.
If desired, the release film A in contact with said laminate may consist of two or more elements, at least one of which has a breaking elongation of no less than 600% but all of them have a 100% elongation load of no more than 350 gf per unit width of 1 cm at the temperature to which said laminate is heated.
In a preferred embodiment, at least the stripping film A in contact with the laminate evolves gas in no more than 5 ppm at the temperature to which the laminate is heated.
In another preferred embodiment, at least the stripping film A in contact with the laminate is formed of a cast molded polytetrafluoroethylene film.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.
REFERENCES:
patent: 4680075 (1987-07-01), McNeal et al.
patent: 4737208 (1988-04-01), Bloechle et al.
patent: 5116440 (1992-05-01), Takeguchi et al.
patent: 5573622 (1996-11-01), Hass et al.
patent: 5626713 (1997-05-01), Yamaguchi et al.
Iimura Mitsuo
Sato Kenji
Tachibana Toshimitsu
Lam Cathy
McGinn & Gibb PLLC
Nitto Denko Corporation
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