Thermal fatigue behavior of flip-chip joints with lead-free solders

Thermal cycle tests were performed for Rip-chip joints with several lead-fret solders in order to research the thermal fatigue behavior of the joints. A joint with Sn-3.5Ag solder was ruptured by solder cracking in the neighborhood of the joint interface. A joint with Sn3.5-Ag-0.76Cu solder was ruptured by interfacial cracking at the Al/Ni interface, and the lifetime before the rupture was shorter than that of the Sn-3.5Ag solder. Although the rupture modes were different, both joints showed a sufficient fatigue life to tolerate the alignment stress in the hip-chip bonding process. In the case of a joint with Sn-1.9Ag-0.52Cu-7.6Bi solder, an interfacial crack was observed in the joint immediately after reflow soldering. Bi segregation was found in the cracked interface. The cracked microstructure was similar to the structure of lifted-off joints often observed when soldering through-holt circuits with Bi-bearing solder. These thermal cycle test result with Sn-3.5Ag and Sn-3.5Ag-0.76Cu solders demonstrate that there is a possibility of using flip-chip joints with these solders for conventional electronic applications.