Interfacial reactions between Sn–Ag lead-free solders and polycrystalline and single-crystal copper

With the trend of solder joint miniaturization, the proportion of interfacial intermetallic compounds in the overall solder joint structure has increased, making interfacial reactions and microstructures key factors that restrict solder joint performance. As a widely used pad material in electronic packaging, the grain boundaries of polycrystalline copper can interfere with the accurate analysis of interfacial reaction laws. In contrast, single-crystal copper can effectively eliminate grain-boundary interference and reveal the intrinsic growth law of interfacial intermetallic compounds (IMC), thereby possessing irreplaceable value in research on micro-solder joint reliability. Based on this, this study investigates the interfacial reactions during the reflow process and subsequent aging reactions of two solders, namely Sn3.5Ag0.5Bi8In and Sn3Ag0.5Cu, on polycrystalline copper and single-crystal copper with (001) and (111) orientations, respectively, at 260 °C and 285 °C. By investigating the morphological evolution and growth behavior of interfacial IMCs on pads with different orientations and combining comparative analysis, the influence mechanism of polycrystalline copper/single-crystal copper pads on the morphological evolution and growth behavior of IMCs at the Sn–Ag series solder/Cu interface is revealed.