Effect of Morphological Change of Ni3Sn4 Intermetallic Compounds on the Growth Kinetics in Electroless Ni-P/Sn-3.5Ag Solder Joint

Abstract

Recently, the growth kinetics of the intermetallic compound (IMC) Ni3Sn4 related to Ni metallization has been investigated in comparison to Cu6Sn5 growth on Cu metallization. In the literature, Ni3Sn4 growth in liquid Sn was analyzed for IMC morphology, grain coarsening, grain boundary (GB) grooving, and GB diffusion. However, the growth kinetics of Ni3Sn4 on electroless (EL) Ni-P metallization has rarely been investigated. In this study, the morphological change of Ni3Sn4 on EL Ni-P and its effects on growth kinetics were analyzed in detail during a reaction with Sn-3.5Ag at 250 °C for up to 30 minutes and compared with electroplated (EP) Ni. For both cases, the IMC growth kinetics was presumed to be governed by fast GB diffusion accompanied with grain coarsening. The morphology of Ni3Sn4 on EP Ni changed little throughout the reaction. Therefore, a 1/3 power-law could be applicable. However, the aspect ratio (thickness/diameter) of the Ni3Sn4 grains on EL Ni-P decreased with the increasing reaction time, which resulted in a larger time exponent of 4.2. The morphological change from needle to chunk induced a high rate of grain coarsening. Consequently, the IMC growth rate declined according to the reduction of fast diffusion paths (GB area).