Interfacial Reactions Between Lead-Free Solders and Ni-Pd-Co Alloys

Abstract

The liquid/solid interfacial reactions of Sn, Sn-(3.0 wt.% to 0.5 wt.%)Cu (SAC), and Sn-9.0 wt.%Zn (SZ) solders with Ni-xPd-yCo substrates at 240°C, 270°C, and 300°C for 0.5 h to 5 h have been investigated. The Ni-xPd-yCo alloys were prepared with x = 0.5 wt.% and 1.5 wt.% and y = 0.5 wt.%, 1.5 wt.%, and 3.0 wt.%. The intermetallic compound (IMC) Ni3Sn4 formed in the Sn/Ni-xPd-yCo reaction couples at 240°C, 270°C, and 300°C. Although (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 phases appeared at the interface of the SAC/Ni-xPd-yCo couples after 0.5 h to 2 h at 240°C, only (Ni,Cu)3Sn4 phase formed after 5 h at 240°C or 0.5 h to 5 h at 270°C or 300°C in the SAC/Ni-xPd-yCo systems. The SZ/Ni-xPd-yCo interfacial reactions at three different temperatures formed the Ni5Zn21 phase, but when the reaction time was extended to 5 h, Ni5Zn21, Sn, and δ phases were also observed. The thickness of the IMCs was measured and used to calculate the reaction rate constant and activation energy. The interfacial reactions between the lead-free solders (Sn, SAC, and SZ) and Ni-xPd-yCo substrates were determined to be diffusion controlled.