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

Thermal cycle tests were performed for Rip-chip joints with several lead-fr et 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 neighb orhood of the joint interface. A joint with Sn3.5-Ag-0.76Cu solder was rupt ured by interfacial cracking at the Al/Ni interface, and the lifetime befor e the rupture was shorter than that of the Sn-3.5Ag solder. Although the ru pture 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 obs erved in tile joint immediately after reflow soldering. Bi segregation was found in the cracked interface. The cracked microstructure was similar to t he structure of lifted-off joints often observed when soldering through-hol t 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 o f using flip-chip joints with these solders for conventional electronic app lications.