Acceleration of the growth of Cu3Sn voids in solder joints

Abstract

Soldering to Cu surface finishes usually leads to the formation of a bi-layer intermetallic structure, Cu3Sn/Cu6Sn5, that provides a more robust bond than common alternatives. Occasionally, and so far unpredictably, voids may however grow within the Cu3Sn over time and allow for premature failure of microelectronics products in service. A quantitative assessment of the reliability risk of voids observed after accelerated aging requires the knowledge of the variation of void growth with temperature and time. It is argued that in the case of realistic solder joints diffusion controlled void growth kinetics are unlikely to follow simple Arrhenius and parabolic dependencies, respectively. Nevertheless, three very different sets of samples were all shown to exhibit void growth that could be well approximated by a parabolic time dependence and an effective activation energy of 0.65–0.80eV.