Effect of solder volume on interfacial reaction between Sn-3Ag-0.5Cu solder ball and Cu Pad after multiple reflows

The effect of solder volume on the interfacial reactions between Sn-3.0Ag-0.5Cu solder balls and Cu pads during reflow soldering was investigated. Sn-3.0Ag-0.5Cu solder balls of 200, 300, 400, and 500 μm in diameters were employed to react with Cu pads on PCB with the opening diameter of 250 μm The reflow profile was set to reach a peak temperature of 250 °C and maintain a duration of 45 s above the liquidus line. The effect of solder volume on the interfacial reaction was obviously demonstrated in this study. Scallop-type Cu6Sn5 grains formed at the interface and grew into a continuous intermetallic compound (IMC) layer as the reaction time prolonged. The average diameter of Cu₆Sn₅ grains and the thickness of Cu₆Sn₅ IMC layer for the smaller volume of Sn-3.0Ag-0.5Cu solder ball were significantly larger than those for the larger Sn-3.0Ag-0.5Cu solder ball after the same reflow, but the Cu consumption of the smaller ball was lower than that of the larger one. For the same diameter solder ball, the average diameter of Cu₆Sn₅ grains, the thickness of Cu₆Sn₅ DVIC layer and the Cu consumption all increased with increasing reflow times, due to increasing reaction time between liquid solder and Cu pad. The growth of interfacial Cu₆Sn₅ layer was affected by the dissolution of Cu pad into molten solder; in turn, it also took influence on the dissolution behavior of Cu into molten solder. Compared with our previous study, Sn-3.0Ag-0.5Cu solder ball consumed less Cu than Sn-3.5Ag solder ball for the same volume ball and after the same reflow; the average diameter of Cu₆Sn₅ grains and the thickness of Cu6Sn5 DVIC layer of Sn-3.0Ag-0.5Cu solder balls were both larger than those of Sn-3.5Ag solder balls after the same reflows and in the same diameters.