Transformation of SAC (Sn3.0Ag0.5Cu) nanoparticles into bulk material during melting process with large melting-point depression

The experimental observation of the transformation of nanosized SAC (Sn3.0Ag0.5Cu) into bulk-sized SAC during the melting process involving a large melting-point depression, using DSC (differential scanning calorimetry) and the reflow test is documented. They manufactured the nanosized SAC in dielectric benzyl alcohol using the modified direct-current arc method. The nanoparticles were spherical in shape with a size distribution of 5-10 nm. Using DSC, the endothermic peaks were continuously measured twice without changing the nanosized SAC. During the initial measurement, they observed peaks at 133, 162 and 217°C. However, in the second cycle, they observed only one peak at 217°C, which indicates the SAC nanoparticles have been completely melted and changed into bulk-sized SAC in the first cycle. They first conducted a reflow test of the SAC nanoparticles suspended in benzyl alcohol including flux on a printed circuit board and a hot plate which are 170°C. It was observed that SAC nanoparticles were transformed into bulk-sized SAC during the melting process at 170°C in less than 3 min. After the melting process, they also observed the formation of thin-layer geometry of SAC with 100 nm and intermetallic Cu6Sn5 between the SAC thin layer and a copper plate on PCB.