GROWTH KINETICS OF INTERMETALLIC COMPOUNDS DURING INTERFACIAL REACTIONS BETWEEN SnAgCuGa LEAD-FREE SOLDER AND Cu SUBSTRATE

Abstract

Sn–Ag–Cu based alloys are well known as an important series of lead-free solders. Gallium has been found to be beneficial for the melting point of the Sn–Ag–Cu solders. In the present work, interfacial reactions between Sn–3.0Ag–0.5Cu–xGa (x = 0, 0.1, 0.5, 1.5 in wt.%) solders and Cu substrates have been examined. The solder and substrate couples were annealed at 80 ºC for 2, 4, 6, 12, 18, and 24 days, respectively. Various layers of intermetallic compounds have been observed to form using scanning electron microscopy. It has been found that only Cu₆Sn₅ phase forms when Ga additions are 0, 0.1 and 0.5 in wt.%; but Cu₃Sn and Cu₉Ga₄ form if Ga addition reaches 1.5 wt.%. Thicknesses of these intermetallic compounds have been measured at different annealing stages in order to study the growth kinetics. The growth of all the intermetallic compounds follows the parabolic rule.