Flip-chip soldering to bare copper circuits

A process for providing highly reliable high-yield controlled-collapse ship connection (C4) joining to bare copper circuitry is described. It was studied in the course of implementing a major change in IBM's metallized ceramic and metallized ceramic polyimide (MCP) production line. The study involved joining chips with 95/5 Pb/Sn C4 solder bumps to bare copper pads on substrates to replace dip-tinned substrates with 90/10 Pb/Sn coated pads. Included is an extensive analysis of the C4 intraconnection. Over 30000 chips were joined to ceramic substrates to characterize wetting to the copper pads, evaluate C4 fatigue life, and assess any reliability impact of natural and artificially induced defects in the C4 columns or wetted pad surface. Statistically, combining the self-removal of contaminants in C4 jointing, the small area a partial wet must have wet a pad, the location dependency for a failure, and the probability of contamination, there is no effect on product reliability.<
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