Aging treatment characteristics of solder bump joint for high reliability optical module

The joint strength and fracture surfaces of Sn–37 mass% Pb and Au stud bumps for photo diode packages after isothermal aging testing were studied experimentally. Al/Au stud bumps and Cu/Sn–37 mass% Pb solders were adopted, and aged for up to 900 h to analyze the effect of intermetallic compound (IMC). The joint strength decreased with aging time. The diffraction patterns of Cu 6Sn 5, scallop-shaped IMCs, and planar-shaped Cu 3Sn were characterized using transmission electron microscopy (TEM). The formation of Kirkendall voids and the growth of IMCs at the solder were found to be a possible mechanism for joint strength reduction.