Tin-bismuth solder connection having improved high temperature p

Details Tin-bismuth solder connection having improved high temperature p Tin-bismuth solder connection having improved high temperature p

1993-04-02

1994-06-14

Heinrich, Samuel M.

Metal fusion bonding

Process

Plural joints

22826261, H05K 334

Patent

active

053202724

ABSTRACT:
In an electronic package, a solder connection for bonding faying surfaces is formed of tin-bismuth alloy comprising a tertiary metal, preferably gold or silver, in an amount effective to increase the melting temperature of the alloy and enhance mechanical properties of the connection at elevated temperatures typically encountered during operation. A process for forming the solder connection comprises applying a film of the tertiary metal onto at least one faying surface and thereafter applying tin-bismuth solder paste onto the film. Preferably, a plate of tin-bismuth alloy is first electroplated onto the faying surface, onto which the tertiary metal is plated. During heating to reflow the solder, the tertiary metal dissolves to produce a uniform liquid that forms the connection.

REFERENCES:
patent: 4636073 (1987-01-01), Williams
patent: 4761699 (1988-08-01), Ainslie et al.
patent: 5156997 (1992-10-01), Kumar et al.
patent: 5186383 (1993-02-01), Melton et al.
patent: 5221038 (1993-06-01), Melton et al.
American Society for Metals, "Soldering", Welding, Braising and Soldering, vol. 6, Metals Handbook, 9th Edition, 1983, pp. 1069 through 1076.
Murphy, Jim "Tin-Bismuth Alloy Plating, a Fusible Low Temperature Etch Resist for High Aspect Ratio PC Boards", presented at IPC Fall Meeting, Oct. 7, 12, 1990, San Diego, Calif.
Prints, A. et al., Phase Diagrams of Terniary Gold Alloys The Institute of Metals, London (1990).

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