Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
1999-06-30
2001-07-31
Gaffin, Jeffrey (Department: 2841)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S256000, C174S255000
Reexamination Certificate
active
06268569
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to printed wiring board assemblies, and particularly concerns printed wiring board assembly that may be utilized over extended periods of time in relatively high-temperature operating environments.
BACKGROUND OF THE INVENTION
It is conventional practice in connection with the manufacture of printed wiring boards to adhere an electrically-conductive metal lamina upon a thin, glass fabric-reinforced, polymerized resin substrate, to then selectively coat desired electric current pathways on the adhered metal lamina with a photo-sensitive etchant resist, and to afterwards remove unprotected portions of the metal lamina from adhesion to the substrate component by etching whereby only electrical current pathway metal remains adhered to the reinforced and polymerized resin substrate. Subsequently, mounting holes for the leads of various to-be-added electrical circuit elements are drilled through the retained pathway metal and supporting substrate, the electrical leads of various added electrical elements are inserted in the mounting holes, and the inserted electrical leads are afterwards soldered to the pathway metal by dipping of pathway metal and inserted leads into a pool of molten solder. Another conventional method used for creating metal pathways is to selectively plate conductive materials directly onto the reinforced and polymerized resin substrate.
Also, the known printed wiring boards have hereto been manufactured using conventional resins such as known epoxy, bismaleimide, or cyanate resin systems for the assembly glass fabric-reinforced substrate component. The use of such resin systems in the substrate component have consequently and undesirably required the use of solders that have lower melting temperatures and lower operating environment temperatures than those of the comparatively high-temperature solders that may be advantageously utilized in the practice of our invention. Further, the conventional or prior art printed wiring boards have necessarily utilized a less-dense spacing of inserted electrical component leads than can be advantageously obtained by practice of our invention.
The above-mentioned advantages of the present invention are attributed primarily to the nature of the resin system we utilize in the manufacture of the printed wiring boards, to particular resin system and reinforcement processing to form the printed wiring board substrate component B-staged preform, or completely cured preform, and to the improved adhesion of electrical current pathway metal, usually copper, to the substrate component B-staged preform that is obtained in the course of subsequent metal cladding lamination or alternatively adding metal to the completely cured preform by chemical, plasma, or ion vapor deposition. Still other advantages of the present invention will become apparent during consideration of the various descriptions which follow.
SUMMARY OF THE INVENTION
The present invention involves the sequential steps of dissolving nadic end-capped polyimide monomer precursors in a methanol-based solute, uniformly impregnating a reinforcement material (glass, quartz, etc.) with the resulting polyimide-containing precursor solution, processing the impregnated reinforcement through a condensation reaction to thereby produce a B-staged substrate preform, and afterwards subjecting the substrate preform to a thermally-induced crosslinking reaction to form a completely cured preform. A conducting film is bonded to the preform either by (1) simultaneously adhering a previously-formed metallic film to the B-staged preform surface during the thermally-induced crosslinking reaction to form a resulting printed wiring board core, such being accomplished at preferred temperatures, pressures, and times at temperature and pressure, or by (2) subsequent deposition of an electrical conductor by chemical, plasma, or ion vapor deposition on the completely cured crosslinked preformed substrate as masked to form electrical current pathways.
Subsequently, the resulting printed wiring board core may be processed in a conventional manner to selectively remove adhered lamina metal from the principal surface of the core in selected areas as by etching to thereby leave desired electrical current pathways of lamina metal adhered to the core substrate, to provide electrical lead openings through the core substrate and adhered electrical current pathways as by multi-position drilling, to insert electrical device leads in and through the provided electrical lead openings, and to lastly electrically join the electrical device leads to the electrical current pathways by soldering in a conventional manner such as hand, wave, drag and convection reflow soldering with relatively high-temperature solder or other conductive materials. Some additive methods for putting lamina metal on the principal surface of the core are chemical, electro-chemical, plasma, and ion vapor deposition.
REFERENCES:
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patent: 5120569 (1992-06-01), Zupancic et al.
patent: 5414224 (1995-05-01), Adasko et al.
patent: 5442144 (1995-08-01), Chen et al.
patent: 5527998 (1996-06-01), Anderson et al.
patent: 5761801 (1998-06-01), Gebhardt et al.
patent: 6096411 (2000-08-01), Nakatani et al.
Grannells Richard Thomas
Scola Daniel Anthony
Alcala Jose′ H.
Baker, Jr. Thomas S.
Gaffin Jeffrey
National Center for Manufacturing Sciences
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