In-situ study the morphology, growth kinetics and mechanism of Cu6Sn5 at the SnAgCu/Cu soldering interfaces during the cooling stage

In this paper, the IMC (Cu6Sn5) morphology evolution was observed by using Shanghai Light Source Synchrotron Radiation (SSRF) and high-pressure air technology. Comparing with complete reflow experiments, IMC growth data during the cooling stage was obtained to study the growth process of typical Cu6Sn5 grain morphology evolution. The results are as follows: (1) The morphology of interfacial Cu6Sn5 during the cooling stage is changed from scallop to facet or prism. Liquid channels between Cu6Sn5 grains were also in-situ observed. The presence of liquid channels increases the diffusion flux of Cu grain boundaries and reduces the IMC growth activation energy, indicating that the addition of Ag can hinder the lateral merging of Cu6Sn5 grain boundary during the heat preservation. Simultaneously, the channels also promote the vertical growth of Cu6Sn5 grains to get a smaller aspect ratio at Sn-3.5Ag-0.7Cu(SAC3507)/Cu interface than Sn/Cu. (2) The growth thickness of IMC during the cooling stage follows the rule of h=kt, which is the reaction control mechanism of the Cu precipitation interface. (3) The interfacial Cu6Sn5 growth during the cooling stage is affected by the pinning effect of Ag3Sn nanoparticles and the Cu precipitation flux. Finally, under the same soldering conditions, the Cu6Sn5 thickness at SAC3507/Cu soldering interface during the cooling stage is thicker than Sn/Cu.