Ripening Growth Kinetics of Cu6Sn5 Grains in Sn-3.0Ag-0.5Cu-xTiO2/Cu Solder Joints During the Reflow Process

Abstract

The ripening growth kinetics of interfacial Cu6Sn5 grains between Cu substrates and Sn-3.0Ag-0.5Cu-xTiO2 (x = 0, 0.02, 0.05, 0.1, 0.3, and 0.6 wt %) (SAC305-xTiO2) solders were investigated. The results show that the Cu6Sn5 grain morphology is affected by the solder composition and the reflow time. The Cu6Sn5 grain size decreases upon addition of TiO2 and shows a significant decrease when the TiO2 nanoparticle fraction is increased to 0.1 wt %. At higher TiO2 nanoparticle fractions, the Cu6Sn5 grain size increases slightly. The growth of the Cu6Sn5 grains is mainly supplied by the flux of the interfacial reaction and the flux of ripening; the ripening flux plays a dominant role because it is approximately one order of magnitude greater than the interfacial reaction flux. The ripening growth of the Cu6Sn5 grains in the TiO2-containing solder joints is reduced more effectively than that of the Cu6Sn5 grains in the TiO2-free joint. For the SAC305/Cu and SAC305-0.6TiO2/Cu solder joints, the particle size distribution (PSD) of the Cu6Sn5 grains is well fit with the Marqusee and Ross (MR) model when the normalized size value of r/<r> is less than 1, and it is consistent with the flux-driven ripening (FDR) model when the value of r/<r> is greater than 1. On the other hand, for the SAC305-0.1TiO2/Cu solder joint, the Cu6Sn5 grains with a nearly hemispheric scallop shape and the PSD of the Cu6Sn5 grains show good agreement with the FDR model.