Growth Kinetic of Sn-0.7Cu-0.05Ni Solder Paste Subjected to Isothermal Aging

This paper studied the thermal stability of Sn-0.7Cu (SC) and Sn-0.7Cu-0.05Ni (SCN) solder paste after soldering and during subsequent aging. Isothermal aging was conducted for 24, 240 and 480 hours at a temperature of 75, 125, and 150 °C respectively. Characterization focuses on the morphology of intermetallic compound (IMC) and the thickness of IMC after soldering and aging. In addition, growth kinetics of SC and SCN solder paste was determined by using the power law and Arrhenius relationship. Findings revealed that additions of Ni has formed a new (Cu,Ni)6Sn5 interfacial IMC. Additionally, it was found that scallop-type Cu6Sn5 and uniform scallop-type (Cu,Ni)6Sn5 of IMC for as-reflowed IMC phase has changed into layer-type IMC after aged. Besides that, IMC thickness for both solders has increased with prolong aging time and temperature. The interfacial IMC grew faster at high temperature aging. The activation energy of SCN solder was calculated as 39.8 kJmol-1 better than 27.29 kJmol-1 possess by SC solder. The high activation energy of SCN solder may attribute to the inherently slower reaction of Ni with SCN solder compared to the faster reaction between SC Solder and Cu for the IMC growth. Besides that, Ni addition act as obstacle for the diffusion of Cu atom from the substrate and Sn atom from the solder to react each another.