Influence of nano-Sb dopant on IMC growth in Sn-3.0Ag-0.5Cu-xSb solder joints in reflow process

The effect of nano-Sb addition on the growth kinetics of intermetallic compound (IMC) in the joints with Sn-3.0Ag-0.5Cu-xSb (x=0,0.2,1.0,and 2.0%) solder in reflow process was investigated. Scanning electron microscope (SEM) was used to observe the microstructure evolution of soldered joints,energy dispersive X-ray (EDX) and x-ray diffractometer (XRD) were used to identify the IMC phases. The results show that some nano-Sb particles were dissolved in Sn-rich phase,some participated in the formation of Ag₃Sb,and the rest dissolved in Cu₆Sn₅ IMC layer. The thickness of IMC layer decreased when the nano-Sb was added. Under the isochronal conditions, the thickness of IMC layer in all soldered joints was minimum when the amount of nano-Sb increased to about 1.0%. The growth exponent n and diffusion coefficient D for IMC layer were determined by curve-fitting. The results reveal that the growth exponent n and diffusion coefficient D decreased with the increase of nano-Sb content. When the amount of nano-Sb increased to about 1.0%,the growth exponent n and diffusion coefficient D were 0.326 and 10.31×10^-10 cm²/s,respectively. Based on the phase diagram analysis and adsorption theory,Sb had better affinity to Sn,and it could reduce the activity of Sn by forming SnSb compound,resulting in decreased driving force and surface energy for formation of Cu-Sn IMC. Therefore, the growth rate of Cu₆Sn₅ grains was suppressed and the growth of IMC layer was retarded.