Anisotropic dissolution behavior of the second phase in SnCu solder alloys under current stress

The microstructural evolution of the intermetallic compound (Cu6Sn5) in Sn–xCu solder matrix under current stress was investigated by scanning electron microscopy (SEM) and in situ synchrotron X-ray diffraction (XRD). The phase evolution of the Cu6Sn5 was also investigated under thermal aging for comparison. The only XRD crystalline peak (3¯14) of Cu6Sn5 that was detected disappeared under current stress, but not under thermal aging. Ex situ SEM observation of the Cu6Sn5 crystal revealed an anisotropic dissolution behavior. The kinetics of the anisotropic dissolution was also investigated.