Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
1998-10-06
2001-05-08
Gaffin, Jeffrey (Department: 2841)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C428S137000, C442S117000
Reexamination Certificate
active
06229096
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a nonwoven reinforcement for a printed wiring base board, a process for producing the same, a printed wiring base board and a printed wiring board.
2. Description of the Related Arts
Glass fiber fabrics have been used over the past years as a nonwoven reinforcement for a printed wiring base board, but said fabrics suffer from the disadvantages of high dielectric constant and high specific gravity. In recent years, investigations have been made on aramid fiber fabrics in the form of liquid crystal, which, however, fail to meet the requirements of a printed wiring base board in electrical insulation properties because of high hygroscopicity.
In such circumstances, there is proposed the use of thermotropic crystalline polyester fiber which is low in dielectric constant, specific gravity and hygroscopicity as a nonwoven reinforcement for a printed wiring base board. For example, there is described a printed wiring base board using woven fabrics comprising thermotropic crystalline polyester fiber as a reinforcement in Japanese Patent Application Laid-Open No. 36892/1987 (Sho-62). However, in the case of producing a thin fabric of thermotropic crystalline polyester fiber, such problems as its low processability, a high manufacturing cost, inferior uniformity of the resultant nonwoven reinforcement and low handling properties such as resin impregnation properties occur.
There is also proposed the use of, as a nonwoven reinforcement, dry system nonwoven fabrics that are obtained by spun lace method (water-jet entangling method). Nevertheless said nonwoven fabrics fail to suffice the requirement of a nonwoven reinforcement for a printed wiring base board by reason of their poor mechanical performance, low uniformity and evils such as unevenness in thickness which is further enlarged as the a fabric is made thin.
In contrast to the foregoing, wet system nonwoven fabrics (fabrics by sheet-making process) have not only excellent mechanical performance but also high uniformity and besides can be made into nonwoven fabrics free from unevenness even for a thin sheet. For instance, there is proposed paper composed of thermotropic crystalline polyester short fiber and thermotropic crystalline polyester pulp in Japanese Patent Application Laid-Open Nos.47818/1995 (Hei-7) and 170295/1996 (Hei-8).
However, with any of the previous conventional methods it has been far from possible to obtain a nonwoven reinforcement for a printed wiring base board which is excellent in various performances such as uniformity resin impregnation properties, mechanical performance and heat resistance.
In general, heat calendering is carried out in order to enhance the mechanical performance and uniformity of nonwoven fabrics. Nevertheless, the practice of the aforesaid method has caused such a problem that the surfaces of the nonwoven fabric are pressed into the form of film, the pores that are capable of being impregnated with a resin are micronized and also the number of said pores are remarkably decreased, thereby making it difficult to impregnate the nonwoven fabric in whole (deterioration of the resin impregnation properties) and consequently forming a portion where the resin is not impregnated into the nonwoven fabric inside. The portion which is non-impregnated with a resin (air), when present to a large extent, brings about at the time of moisture absorption, unstable electrical insulation properties, inferior heat resistance of a solder and an unfavorable nonwoven reinforcement which is required for advanced performances for a printed wiring base board. Notwithstanding the foregoing, unless a heating pressurizing treatment is carried out, it is impossible to maintain the strength which is endurable to the production process such as resin impregnation step and in addition, a problem arises in dimensional stability.
Although an investigation is made on the production of a printed wiring base board with a fiber-reinforced resin by mixing reinforcing fiber in a resin, the reinforcing fiber is difficult to uniformly disperse in a resin. In addition, the reinforcement effect is restricted by the fiber oriented in random directions.
SUMMARY OF THE INVENTION
The object of the invention is to provide a nonwoven reinforcement excellent in various performances such as uniformity, resin impregnation properties, mechanical performance, heat resistance for use in a printed wiring base board; an efficient production process of the nonwoven reinforcement; a printed wiring base board and a printed wiring board that are excellent in various performances.
Specifically, the invention relates to the following embodiments:
(1) A nonwoven reinforcement for a printed wiring base board which reinforcement comprises a wet system nonwoven fabric constituted of thermotropic crystalline polyester fiber having a melting point of 290° C. or higher (component A) and a thermotropic crystalline polyester binder which has a melting point of 290° C. or higher and is in the form of a film having holes including at least 5 holes/mm
2
each with an area of opening of 400 to 1000 &mgr;m
2
(component B), said component A being fixed by said component B.
(2) The nonwoven reinforcement for a printed wiring base board according to the item (1), wherein the ratio by weight of said thermotropic crystalline polyester fiber (component A) to said thermotropic crystalline polyester binder (component B) is in the range of 20:80 to 90:10.
(3) The nonwoven reinforcement for a printed wiring base board according to the item (1) or (2), wherein the void fraction in said reinforcement is at least 40% and the breaking length thereof is at least 0.6 km.
(4) The nonwoven reinforcement for a printed wiring base board according to the item (1) or (2), wherein the Metsuke (basis weight) of said reinforcement is in the range of 20 to 100 g/m
2
.
(5) A process for producing a nonwoven reinforcement for a printed wiring base board which comprises the steps of producing by wet-system sheet making, paper stuff comprising thermotropic crystalline polyester fiber having a melting point of 290° C. or higher (component A) and a thermotropic crystalline polyester fibrous binder having a melting point lower than 290° C. (component B); heat treating the resultant paper stuff under non-pressurizing condition to melt and bring the component B into a form of film having holes including at least 5 holes/mm
2
each with an area of opening of 400 to 1000 &mgr;m
2
and to fix the component A; and subjecting the component B to solid-phase polymerization to bring the melting point thereof to 290° C. or higher.
(6) A printed wiring base board comprising at least one prepreg which is formed by impregnating or adhesively bonding the wet-system nonwoven fabric described in the item (1) or (2) with a thermoplastic resin or a thermosetting resin.
(7) A printed wiring board which comprises at least one printed wiring base board according to the item (6).
(8) A printed wiring board which comprises at least one printed wiring base board according to the item (6) and at least one copper layer that are laminated with one another.
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patent: 5286330 (1994-02-01), Azuma et al.
patent: 5415738 (1995-05-01), Mehta et al.
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patent: 5631073 (1997-05-01), Riedel et al.
patent: 6033765 (2000-03-01), Takahashi et al.
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patent: 0 603 745 (1994-06-01), None
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patent: WO 93/13940 (1993-07-01), None
Esaki Tamemaru
Gaku Morio
Nozaki Mitsuru
Saimen Kenji
Cuneo Kamand
Gaffin Jeffrey
Mitsubishi Gas Chemical Company Inc.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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