The Solid Liquid Interdiffusion (SLID) bonds carried out for this work take advantage of the Cu-In-Sn ternary system to achieve low temperature wafer-level bonds.The experiments were carried out across a range of temperatures and the results cover optimized wafer-level bonding process, the formation of the bond microstructure, mechanical performance, as well as the effects of thermal aging.

The wafer-level Solid Liquid Interdiffusion (SLID) bonds carried out for this work take advantage of the Cu-In-Sn ternary system to achieve low temperature interconnections. The 100mm Si wafers had µ-bumps from 250µm down to 10µm fabricated by consecutive electrochemical deposition of Cu, Sn and In layers. The optimized wafer-level bonding processes were carried out by EV Group and Aalto University across a range of temperatures from 250C down to 170C. Even though some process quality related challenges were observed, it could be verified that high strength bonds with low defect content can be achieved even at a low bonding temperature of 170C with an acceptable 1-hour wafer-level bonding duration. The microstructural analysis revealed that the bonding temperature significantly impacts the obtained phase structure as well as the number of defects. A higher (250C) bonding temperature led to the formation of Cu3Sn phase in addition to Cu6(Sn,In)5 and resulted in several voids at Cu3Sn|Cu interface. On the other hand, with lower (200C and 170C) bonding temperatures the interconnection microstructure was composed purely of void free Cu6(Sn,In)5. The mechanical testing results revealed the clear impact of bonding quality on the interconnection strength.

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