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GROUNDING SCHEME FOR PRINTED WIRING BOARD ASSEMBLIES MOUNTED IN INJECTION MOLDED PLASTIC HOUSINGS

IP.com Disclosure Number: IPCOM000006804D
Original Publication Date: 1993-Mar-01
Included in the Prior Art Database: 2002-Feb-04
Document File: 2 page(s) / 95K

Publishing Venue

Motorola

Related People

Jim J. Johnson: AUTHOR

Abstract

Electronic products incorporating electronic assem- blies within injection molded plastic housings oflen require reliable, continuous eledrical grounds for operation and/or product qualification testing. Schemata for grounding must(i) meet this continuity requirement, (ii) provide little "Bill of Material" impact and (iii) promote "Design for Assembly" philosophies.

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INC. Technical Developments Volume 18 March 1993

GROUNDING SCHEME FOR PRINTED WIRING BOARD ASSEMBLIES MOUNTED IN INJECTION MOLDED PLASTIC HOUSINGS

by Jim J. Johnson

   Electronic products incorporating electronic assem- blies within injection molded plastic housings oflen require reliable, continuous eledrical grounds for operation and/or product qualification testing. Schemata for grounding must(i) meet this continuity requirement, (ii) provide little "Bill of Material" impact and (iii) promote "Design for Assembly" philosophies.

  A design consistent with principles (i) through (iii) is illustrated in cross-section in Fire 1 and in a sec- tional exploded view in Figure 2. Figures 1 and 2 show an injection molded top housing having a top shoulder boss and clamping rib, an injection molded bottom hous- ing having a bottom shoulder boss, a printed wiring board (PWB) having exposed ground planes disposed on both sides of the PWB in the area where the PWB is cap- tured between the top and bottom shoulder bosses, an external star washer between the bottom shoulder boss and the PWB and a screw securing the top and bottom shoulder bosses as well as the external star washer and

PWB. Thin (a few thousandths of an inch) conductive coatings are selectively disposed on interior surfaces of the top and bottom housings and shoulder bosses by electroless plating of copper and nickel or by applica- tion of a coating of a conductive, nickel-based paint.

  The top and bottom in...