A Comparative Study of Reactive Wetting of Lead and Lead-Free Solders on Cu and (Cu6Sn5/Cu3Sn)/Cu Substrates

Abstract

Reactive wetting of solders on Cu and Cu 6 Sn 5 /Cu 3 Sn/Cu substrates was investigated using both (1) the wetting balance, and (2) the hot-stage real time, in situ visualization of the triple-line movement. To understand the phenomenology of the spreading behavior better, comprehensive real-time in situ observations were performed. It was found that the wetting time during the wetting balance tests for both the lead solder (63SnPb) and lead-free solder systems (SnO.7Cu and Sn3.5Ag) is shorter on Cu substrates than it is on Cu 6 Sn 5 /Cu 3 Sn/Cu substrates. The wetting force was not remarkably different on these two substrates for the same solder system. The hot-stage tests indicate a more pronounced spreading of 63Sn-Pb on Cu 6 Sn 5 /Cu 3 Sn/Cu substrates, along with a much larger spreading area. Spreading of lead-free solders in terms of the triple-line kinetics studied by using the hot-stage visualization shows no significant difference in the spreading evolution either over Cu or over Cu 6 Sn 5 /Cu 3 Sn/Cu substrates.