LAUSR

Interfacial reaction and the growth behavior of intermetallic compound (IMC) between Sn solder and Ni substrate by dip soldering under different aging conditions (120 °C, 170 °C and 200 °C) by using scanning electron microscope were investigated. Experimental results showed that the only scallop-shaped Ni3Sn4 IMC layer formed at the interface after aging process and the thickness of IMC layer increased with prolonged aging time. Moreover, the cracks formed in the interface between IMC and solder could be resulted from the residual stress caused by the difference in thermal expansion coefficients. In addition, the spalling behavior of IMC from substrate was caused by cyclic shear stresses and strains induced and the morphological changes in IMC formation. During the aging process, it was found that the thickness of IMC always had a linear relationship with the square root of aging time under different aging temperatures (120 °C, 170 °C and 200 °C). The growth rate constants of IMC layers aged at 120 °C, 170 °C and 200 °C were obtained by using fitting method from the experimental data, which were 4.65 × 10−18 m2 s−1, 9.94 × 10−18 m2 s−1 and 1.76 × 10−16 m2 s−1, respectively. Based on these data, the activation energy of IMC layer was determined to be 63.23 kJ/mol. Likewise, the mean diameter of IMC grains increased with the increase in aging time. It is suggested that the mean diameter of IMC grains was always plotted against the aging time on a double logarithmic scale under different aging temperatures. The time rate constants of IMC grains aged at 120 °C, 170 °C and 200 °C were obtained by using same method, which were 0.10, 0.27 and 0.26, respectively.