Browse Prior Art Database

Improved Solder Pads

IP.com Disclosure Number: IPCOM000044905D
Original Publication Date: 1983-Jan-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Carpenter, C: AUTHOR [+5]

Abstract

This process eliminates storage/corrosion problems associated with lead surfaces and solder flux joining problems arising from flux removal (chemical treatment of solvents, stack reactants) and from variables of flux-joining process.

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Improved Solder Pads

This process eliminates storage/corrosion problems associated with lead surfaces and solder flux joining problems arising from flux removal (chemical treatment of solvents, stack reactants) and from variables of flux-joining process.

Solder contact pads stored for any period of time tend to corrode because of a Pb-rich surface. That corrosion product requires (a) more frequent electrical test probe cleaning, (b) more stringent storage ambient control, and (c) improved joining process(es). Standard manufacturing techniques provide a pad with a (preferred) Sn-rich surface, but electrical test probes frequently degrade and remove (tear out) the Sn cap such that the pad Sn content drops out of specification. The tin rich surface bonds to substrate pads (Au or PbSn) without flux at temperatures below 300 degrees centrigrade, but the variation of surface Sn continuity has led to the need for flux joining, and the need for a more uniform Sn distribution (to prevent probe Sn tear out) led to a reflow step prior to test and joining.

The following process eliminates the need for preprobe reflow or fluxing. PbSn is deposited by coevaporation from two sources to insure approximately 5% uniform Sn in bulk with final Sn flash or overcoat sputtered alloy deposition or carefully controlled E-gun alloy deposition. The sputtering or E-gun deposition step would be phased to a pure Sn overcoat of 500-1,000 Angstroms. Sn content (bulk) and overcoat control could...