Browse Prior Art Database

Contact Pads for Ceramic Integrated-Circuit Substrates

IP.com Disclosure Number: IPCOM000043387D
Original Publication Date: 1984-Aug-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Krumpelmann, JM: AUTHOR [+2]

Abstract

Conventional ceramic substrates for bonding integrated-circuit chips using C4 (controlled-collapse contact connection or solder-ball) pads have three layers of metal: chrome, copper, and chrome. To solder the chips to the substrate, a photoresist applied to the substrate is exposed with the desired connection pattern and developed. Then the upper chrome layer is plasma etched to expose the copper. While the substrate is still warm, it is placed in an electroless gold bath to plate gold over the C4 pad positions, using the photoresist as a plating mask. The photoresist is thereafter stripped off.

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Contact Pads for Ceramic Integrated-Circuit Substrates

Conventional ceramic substrates for bonding integrated-circuit chips using C4 (controlled-collapse contact connection or solder-ball) pads have three layers of metal: chrome, copper, and chrome. To solder the chips to the substrate, a photoresist applied to the substrate is exposed with the desired connection pattern and developed. Then the upper chrome layer is plasma etched to expose the copper. While the substrate is still warm, it is placed in an electroless gold bath to plate gold over the C4 pad positions, using the photoresist as a plating mask. The photoresist is thereafter stripped off. The advantages of this process over the conventional chemical etching and solder bath include the elimination of thermal stresses from a solder bath, prevention of tarnishing during substrate storage, and increased contact wetting when the chips are joined.

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