Interfacial Reactions in Lead-Free Solder/Cu-2.0Be (Alloy 25) Couples

Abstract

The interfacial reactions between lead-free solders Sn, Sn-3.0 wt.% Ag-0.5 wt.% Cu (SAC) and Sn-9 wt.% Zn (SZ), and Cu-2.0 wt.% Be (Alloy 25) were investigated using the liquid/solid couple technique. The couples were reacted at 240–270°C for 0.5–10 h. The results revealed that only the scallop-shaped (Cu, Be)6Sn5 phase was formed at 240°C for 0.5–2 h in the Sn/Alloy 25 couple. At a longer time (> 4 h) or higher temperature (255°C and 270°C), the (Cu, Be)3Sn phase was observed at the interface. In the SAC/Alloy 25 couple, the results were similar to that in the Sn/Alloy 25 couples. Only the scallop-shaped (Cu, Be, Ag)6Sn5 phase was formed for the short reaction time or at lower reaction temperature. With increasing reaction times and temperatures, both the (Cu, Be, Ag)6Sn5 and (Cu, Be, Ag)3Sn phases were observed at the SAC/Alloy 25 interface. In the SZ/Alloy 25 couple, the (Cu, Sn)Zn5 and (Cu, Sn)5Zn8 phases were observed. Of these three couples, the intermetallic compound (IMC) thickness obeyed the parabolic law, and the IMC growth mechanism was diffusion-controlled.