Reliability and Shear Strength of 42Sn-57Bi-1Ag (Wt.%) Lead-Free Solder Joints after Thermal Aging and Salt Spray Testing

Low cost manufacturing in the electronics industry is becoming more demanding, particularly in the production of consumer electronics. Such manufacturing processes require reliable and low-cost lead-free solders. Among the low temperature lead-free solders, Sn-Bi solder has attracted a great deal of interest since it offers good reliability comparable to that of Sn-Pb solders. In this paper the reliability of eutectic 42Sn-57Bi-1Ag (wt.%) lead-free solder was studied using combinations of environmental tests including thermal aging at 100 degrees C, salt spray test, and a sequential combination of thermal aging and salt spray tests. Microstructural studies on samples were performed at different time intervals. To study the effect of salt spray and thermal aging on the mechanical reliability, shear testing was performed on the samples. Failure analysis including fractography was conducted on samples at different time intervals using scanning electron microscope (SEM). Considerable corrosion was observed after the salt spray test. This corrosion also had a marked effect on the shear strength of the solder joints. It was moreover found that the increase in the thickness of intermetallic layers had an adverse effect on the shear strength. To study the effect of adding 1% Ag to the mechanical properties, a comparison between the mechanical reliability of eutectic Sn-58Bi and Sn-Bi-1Ag is presented.