Growth behavior and microstructure of intermetallics at interface of AuSn20 solder and metalized-Ni layer

The AuSn20/Ni joints were prepared by the reflow soldering technology and then annealed at solid-state temperature to form diffusion couples. The interfacial reactions and the growth kinetics of the intermetallic compounds (IMC) at the AuSn20/Ni soldering interface were investigated by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The results show that, the (Ni,Au)3Sn2 phases are formed at the AuSn20/Ni interface after soldering at 583 K. The thickness l of the IMC layer monotonically increases with increasing annealing time t according to the relationship l=k(t/t0)n, where the exponent n is 0.527, 0.476 and 0.471 for 393, 433 and 473 K annealing, respectively. This indicates that the volume diffusion contributes to the growth of the IMC layer at the AuSn20/Ni interface at solid-sate temperature. The pre-exponential factor K0=1.23×10−7 m2/s and the activation enthalpy QK=81.8 kJ/mol are obtained from the results of the parabolic coefficient K by a least-squares method.