Influence of Small Amount of Solid Phase on Solderability in Wave Soldering Process by using of Sn-Ag-Cu-Ni Based Solder

Abstract

Cu dissolution of electrodes on printed circuit boards (PCB) and Fe erosion of solder baths have been still the problems in wave soldering by SnAg -Cu lead-free solder, because SnAg -Cu alloy is highly reactive to metals compared with Sn-Pb eutectic alloy. The countermeasure to control dissolution rate of Cu is not only increasing Cu concentration, but also increasing Ni concentration in the molten lead-free solder. Although Ni addition is certainly effective to inhibit Cu dissolution in SnAg -Cu solder, liquidus temperature of the solder rises according to Ni concentration. Therefore, it is concerned that solidification of Cu-Ni-Sn intermetallic compound (IMC) phase may occur in molten solder maintained at soldering temperature. In this study, the influence of Ni concentration of Sn-3.0Ag-0.5Cu-xNi alloy on solderability in wave soldering process is investigated by the observation of separating solder joint on PCB from the surface of molten solder with the high-speed VTR. As a result, it is clarified that the partial solidification slightly influences on fluidity of molten solder, but the wave soldering by Sn-3.0Ag-0.5Cu-xNi alloy will be practical even around the liquidus temperature.