Inner microcrack induced by intermetallic compound in right-angle Au/Sn3.0Ag0.5Cu/Au solder joints

With the promptly development of electronic products toward miniaturization and multi-functionalization, the volume of solder joints become smaller and smaller, and which result in a serial of reliability and processing issues, for example, the higher ratio intermetallic compound (IMC), the lower mechanical properties, the soldering process and the higher rejection rate, etc. Previous literature on the shocking resistance of right-angle Au/Sn3.0Ag0.5Cu(SAC305)/Au solder joints has shown that with the decreasing of the volume, the ratio of the brittle phase - IMC in the matrix of solder joints obviously increases, which further result in the poorer mechanical shocking resistance of right-angle solder joints fabricated by the solder balls with more smaller diameter. It is imperative to further investigate that the mechanical properties and the reliability fabricated by the more smaller solder balls for the electronic packing. In this study, the inner microstructure of right-angle Au/SAC305/Au solder joints fabricated by the smaller solder ball with the diameter of 50 µm were investigated by employing scanning electron microscopy (SEM) and energy-dispersive Xray spectroscopy (EDX), and the deterioration of the mechanical properties of solder joints was analyzed on the basis of the inner microstructure. Owing that the solder ball become smaller, there is an obviously sagging curve on the surface of solder joints. The SEM results of cross section of solder joint show that the inner microcracks easily formed at the top corner of the right-angle solder joints, and there are different IMCs at both sides of the microcracks at there. The analysis manifest that the disregistry between the different IMCs and the difficult feeding are the key factors of the inner hidden microcrack.