Effect of burn-in on shear strength of 63Sn-37Pb solder joints on an Au/Ni/Cu substrate

A study was performed to examine the effect of burn-in and Au-plating thickness on the shear strength of 63Sn-37Pb solder joints in ball grid array (BGA) packages. The Au-plating thicknesses of 0.3 mum, 0.6 mum, 0.9 mum, and 1.4 mum were evaluated. An isothermal aging temperature of 150degreesC was employed to simulate burn-in conditions. The evolution of the bulk solder microstructure and intermetallic compounds at the solder joint interface were characterized and correlated to the measured shear strength. The strength of the solder joints with 0.3-mum Au plating was approximately three times higher than the thicker platings after aging. Solder joints with 0.3-mum Au plating failed within the solder matrix, and their strength was dependent upon the bulk solder microstructure and composition. The weakness of the solder joints with thicker Au platings was attributed to the formation of a brittle AuSn4/Ni3Sn4 interface and a ductile Pb-rich layer at the interface.