Sn-Bi(-Ga) TIM Alloys: Microstructure, Tensile Properties, Wettability and Interfacial Reactions

Abstract

In the present study, the main purpose is to examine the quality of the interface formed between either binary Sn-Bi or ternary Sn-Bi-2wt.%Ga Thermal Interface Material—TIM alloys and a copper (Cu) substrate. The characteristics of the formed intermetallic compound (IMC) films were analyzed in the as-soldered joints, as well as during isothermal heat treatments at 100°C for long periods of time. Thermo-Calc computations were also used in return for a better comprehension of the mechanisms involved, including, for instance, those related to the presence of Ga within the interdendritic regions. This can be explained by the increase in the Ga-amount in the liquid-phase with the progress of solidification. In an effort to address the wettability issue, the contact angles between the molten alloy and the Cu substrate were also determined. Finally, tensile tests were performed in order to evaluate the effects of the minor Ga additions in the alloy’s overall mechanical properties. Despite unsound alloy mechanical properties, gallium (Ga) additions effectively suppress the formation of the CuSn intermetallic by replacing it with a Cu9Ga4 IMC layer in the as-soldered material, which grew with less deleterious morphology and finer thicknesses.