Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1995-06-07
2000-10-31
Lam, Cathy F.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525 57, 26433115, C08F 1606
Patent
active
061404152
ABSTRACT:
Thermoplastic printed wiring board spacers are fabricated by providing a water soluble partially hydrolyzed polyvinyl alcohol resin or fully hydrolyzed polyvinyl alcohol resin or a blend of partially hydrolyzed polyvinyl alcohol resin and fully hydrolyzed polyvinyl alcohol resin, the ratio thereof depending upon (1) the degree of hydrolyzation of the polyvinyl alcohol resins, (2) crystallinity associated with particular polyvinyl alcohol resins, (3) the fabrication temperatures of the printed wiring board to avoid spacer melting and (4) the degree of solubility in water of the spacer. The spacers are fabricated by injection molding the polyvinyl alcohol resins or desired polyvinyl alcohol resin mixture to provide a molded configuration having a runner system with spacers attached to a sub runner system by a very thin gate. The spacers are removed from the molded configuration by initially cooling the surface of the total molded configuration to a temperature at which the thin gate sections becomes very brittle. The cooled molded configuration is then subjected to tumbling or a jolt whereby the spacers break away from the runner system at the gates. As an alternative embodiment, the spacers as molded include ridges and recessed areas therein along one or preferably both opposite surfaces which, when in placed around component leads, permit gases emitted during the soldering process to have an avenue of escape and provide for increased exposed surface area to prevent premature melting of the spacer by keeping it cool during flow/wave solder process and provide greater surface area available to the solvent, resulting in more rapid dissolving of the spacer material during the spacer removal step.
REFERENCES:
patent: 3300546 (1967-01-01), Baechtold
patent: 4228250 (1980-10-01), Pritchett
patent: 4481326 (1984-11-01), Sonenstein
patent: 4692494 (1987-09-01), Sonenstein
patent: 4904509 (1990-02-01), Nohara et al.
patent: 5436293 (1995-07-01), Hayes et al.
Brady III Wade James
Lam Cathy F.
Telecky Jr. Frederick J.
Texas Instruments Incorporated
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