Reliability Evaluation of Lead-Free Solders for Automotive Applications

Thermal shock and thermal cycle tests in the temperature range from -40 oC to +150 oC was performed to understand the joint reliability of Sn3.5Ag, Sn0.7Cu and Sn5.0Sb. For the thermal tests, the solder balls of the BGA test chips were fabricated using the materials. The the chips are assembled to a daisy chain PCB. Thermal shock tests as well as thermal cycle tests were performed, and the resistance of the solder joints was monitored during the test. To analyze the failure, microstructure with respect to IMCs morphologies and thickness was analyzed and compared. The shear strength was also measured depending on the thermal cycles. A preliminary stress analyses was also conducted by numerical simulation. It was found that Sn0.7Cu exhibited superior mechanical properties among the investigated solder materials in the present test method.