Determination of optimal solder volume for precision self-alignment of BGA using flip-chip bonding

Flip-chip has a pronounced advantage over alternative interconnect technologies such as wire-bonding and TAB due to its ability to exploit area versus perimeter bonding. Another important aspect of flip-chip bonding is that it can offer "automatic" self-alignment. In this presentation, we report on recent efforts by us to determine the optimal amount of solder volume which is required to obtain the maximum restoring force for self-alignment. We further examine issues relating to the bond pad size and shape, solder composition, solder bump height (prior to and after reflow), and the effects of these choices on the self-alignment forces.