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Browse Prior Art Database

CHIP CARRIER LOW PROFILE BURN-IN

IP.com Disclosure Number: IPCOM000006831D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2002-Feb-06
Document File: 3 page(s) / 162K

Publishing Venue

Motorola

Related People

Ruben Rivera: AUTHOR [+3]

Abstract

In the never ending quest for smaller product size, Motorola portable radios and pagers use a variety of surface mounted chip carriers. The chip carriers con- tain microcomputers, peripheral function chips, and memory chips. The chip carrier footprints vary from having pads on the outer edges of the substrate to highly dense pad array carriers. The chip carriers require testing at the component level, and chip carriers containing embedded EEPROM also require burn-in to screen for infant mortality failures inherent with EEPROM tech- nology. It has always been a challenge to contact these devices for testing and bum-in purposes.

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MOTOROLA INC. Technical Developments Volume 19 June 1993

CHIP CARRIER LOW PROFILE BURN-IN

by Ruben Rivera, Victor Sklarenko and Dave Ellis

  In the never ending quest for smaller product size, Motorola portable radios and pagers use a variety of surface mounted chip carriers. The chip carriers con- tain microcomputers, peripheral function chips, and memory chips. The chip carrier footprints vary from having pads on the outer edges of the substrate to highly dense pad array carriers. The chip carriers require testing at the component level, and chip carriers containing embedded EEPROM also require burn-in to screen for infant mortality failures inherent with EEPROM tech- nology. It has always been a challenge to contact these devices for testing and bum-in purposes.

  Great success has been achieved using spring probes (or pogo pins). Spring probes are mounted in a plastic block in the shape of the chip carrier's footprint. A guide plate to align the chip carrier over the probes and a hinged lid to hold the chip carrier down against the probes com- pletes a spring probe socket. The spring probe socket is mounted on a test system fixture. Chip carriers to be tested are pressed down against the spring probes on the Iixture during testing to make electrical contact.

  The spring probe solution does have some restric- tions as a contacting scheme. The greatest restriction is the one of physical space required above the chip w- rier location. Because spring probes are approximately one halfinch in length, a spring probe socket will be this height plus the chip carrier thickness plus the thickness of the socket lid. Typical socket heights approach 1.25 inches.

  The height restriction has not been a concern for test tixtures. Parts are tested one at a time on handling equipment that can easily compensate for the additional height of the spring probe sockets. However, the restric- tion is of critical concern with regard to bum-in hxturing. The standard Wakefield burn-in ovens available for bum-in of the portable radio and paging chip carriers have very specific height restrictions. The spring probe socket bum-in fixtures exceed these height restrictions. The solution in the past was to use every other burn-in board slot which effectively halved oven capacity.

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ELASTOMER

  Recent advancements in elastomer technology have improved the materials contact density and operational temperatures. Elastomers are widely used to connect LCD modules to printed circuit boards. Elastomer refers to a rubberized sheet material which has been impreg- nated with conducting material. Elastomer is ansiotropic, that is, the conducting material is located in such a way that electrical signals flow from one side of the sheet through to the other side of the sheet but do not flow elsewhere. This feature allows elastomer to be used as a contacting medium between the footprint of an electri- cal component and a printed circuit board. The elasto- mer connects the corres...