Metal fusion bonding – Process – Plural joints
Patent
1993-04-05
1994-05-31
Heinrich, Samuel M.
Metal fusion bonding
Process
Plural joints
22826261, 437209, 174259, 420562, H05K 334
Patent
active
053162056
ABSTRACT:
A gold bump contact on an electronic component is solder bonded to a bond pad of a printed circuit board or the like utilizing a solder composed of tin-bismuth alloy. The solder is applied to the bond pad as an electroplate or a paste, after which the gold bump is superposed onto the bond pad. The assembly is heated to a first temperature to melt the solder and thereafter maintained at a temperature less than 150.degree. C. to permit the molten solder to wet the gold surface, after which the assembly is cooled to solidify the solder and complete the connection. Wetting at the relatively low temperature retards dissolution of the gold and thereby reduces formation of unwanted gold tin intermetallic compounds that tend to decrease mechanical properties of the connection.
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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).
Fekete Douglas D.
Heinrich Samuel M.
Motorola Inc.
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