Abstract
Flip chip joints on the epoxy base substrates were formed with Au bumps and several lead-free solders in order to evaluate the thermal fatigue behavior of those joints. The thermal cycle test and the observation of microstructures were performed with them. It was cleared that the joint with Sn or Sn-3.5Ag solder was almost changed to the Au-Sn intermetallics just after reflow soldering. On the other hand, no excess formation of intermetallics was found on the joints with other solders except Sn and Sn-3.5Ag. As the results of the thermal cycle test, it was found the indium base solders, such as In-48Sn, In-3Ag and pure In, showed the excellent thermal fatigue lifetimes. In these solders, the deformation of solder itself were observed after the thermal cycle test, and the main fracture mode was the solder cracks in the joints. That result indicates the indium base solders, which shows the good lifetime, are easily deformed against the thermal stress and released the stress by the deformation itself.
