Study of intermetallic compounds (IMC) that form between indium-enriched SAC solder alloys and copper substrate

Abstract

This paper evaluates the characteristics of the intermetallic compounds (IMC) that form between Indium-enriched SAC solder alloys and Copper substrate. In this study, Indium was added to a commercial SAC305 solder (96.5 wt.% Sn, 3 wt.% Ag, 0.5 wt.% Cu) at three different compositions, 0.5, 5, and 10 wt%. To observe IMC growth during the liquid state of the solder droplet, the experimental matrix consisted in three soldering temperatures (220, 275, and 300 °C), and the molten solder was kept at this temperature for 2, 5, and 8 s. Fast cooling followed each solder test to complete solidification. The same procedure was repeated for the three levels of Indium. The Copper substrate/solder alloy interface was examined using light microscopy, scanning electron microscopy, and energy dispersive spectroscopy. Statistical analysis was performed on the IMC thickness data obtained from the long profile analyses. Using Arrhenius analysis, the activation energy for IMC formation and growth was calculated to be approximately 6.7, 5.1, and 10.8 kCal/mol for the SAC305 alloys with 0.5, 5.0, and 10 wt% Indium additions, respectively. As expected, Cu6Sn5, Cu3Sn, Ag3Sn, In3Sn (β), InSn4 (γ), and AgIn2 were observed.