Interfacial reactions between eutectic SnZn solder and bulk or thin-film cu substrates

Interfacial reactions between eutectic SnZn solder and bulk or thin-film Cu substrates are investigated and compared.. The thicknesses of bulk and thin-film Cu substrates are 0.5 mm and 4,000 A, respectively. Different dominant reaction products and interfacial microstructures are observed in these two types of interfacial reactions. In the bulk Cu type, the Cu5Zn8 phase is the dominant reaction product under reflow and solid-state annealing. However, the CuZn5 phase becomes the dominant reaction product in the thin-film Cu type. The Cu5Zn8 phase in the bulk Cu type remains as a uniform microstructure after reflow. After solid-state annealing, however, the Cu(5)Zns phase fractures and the Cu6Sn5 and Cu3Sn phases are formed at the Cu5Zn8/Cu interface. The CuZn5 phase in the thin-film Cu type ripens after reflow and the phase morphology is transformed from a uniform layer into separated scallops. In situ observation of the interfacial microstructure after solid-state annealing reveals that prominent deformation occurs in the solder region close to the interface in the bulk Cu type. While in the thin-film Cu type, the CuZn5 grain is extruded out of the interface.