ABSTRACT
Emerging environmental regulations worldwide, most commonly in Japan and Europe, have targeted the elimination of lead in electronic products. Pure tin (Sn) and eutectic tin-copper (Sn-Cu) alloy are two possible candidates to replace tin-lead (Sn-Pb) as the solder bumping materials for flipchip bonding. Without Pb, the stability of the Sn-Cu interface during reflow suffers from the rapid dissolution of Cu into molten Sn. The requirements of multiple reflow during the flip-chip manufacturing steps further complicate the issue. In some severe cases, some intermetallic droplets can move to the top surface of the bumps, which can cause failures during the flip-chip bonding process.
