Wetting characteristics and liquid-solid state reaction of Co-P films for low silver Sn-0.45Ag-0.68Cu-Ni-P solder

Wetting characteristics and liquid-solid state reaction between low silver Sn-0.45Ag-0.68Cu-Ni-P solder and Co-P films and Cu substrate at 250 °C were investigated. The microstructure evolution and composition of the interfacial intermetallic compounds (IMCs) at the interface of the solder and Co-P films were determined by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The dynamic wetting curve on substrate with Sn-0.45Ag-0.68Cu-Ni-P solder showed that the maximum wetting force between solder and Cu substrate was 2.80 mN under 20s dipping time. However, the wetting forces of solder on Co-P films were small compared to Cu substrate. Among three kinds of Co-P films, the maximum wetting force was the largest on the Co-5.0 at.% P film and the smallest on the Co-13.0 at.% P film. The result of interfacial reaction showed that the morphology, composition and thickness of the IMCs at the interface of Sn-0.45Ag-0.68Cu-Ni-P solder on Co-P were different from Cu substrate with dipping times. The Co-P film could inhibit the growth of the IMCs compared to Cu substrate. The thickness of IMC layer on the Co-P films was thinner than that of on Cu substrate. CoSn3 and (Cu, Co, Ni)6Sn5 IMCs were observed at the interface between the solder and Co-5.0 at.% P, while thin Co-Sn-P IMC was found at the interface between the solder and Co-13.0 at.% P and Co-15.0 at.% P films. With the increase of the P content in Co-P films, (Cu, Co)6Sn5 IMC decreased and needle-like (Cu, Co)Sn3 appeared. The effect of the phosphorous content of Co-P film on the growth rate of the IMCs was obvious.