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

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.