Abstract
The formation of large Ag3Sn plate in Sn-Ag solder joint has restricted its application in lead-free electronic industry. There is a great interest for finding new approach to suppress the growth of Ag3Sn. In this paper, Sn-2.1Ag and Sn-1.8Ag-9.4In solder bumps are prepared by electroplating of Sn-Ag and indium in sequence. After reflow at 260°C for 30 min with cooling rate 0.33°C/s, the phase composition, microstructure and undercooling of solder alloys are characterized by X-ray diffraction, Scanning electron microscopy and Differential scanning calorimeter, respectively. It is found that after indium addition, large Ag3Sn plate is substituted by Ag9In4 with irregular polygon morphology. It is also found that indium addition can significantly reduce the undercooling of β-Sn, which promotes the solidification of β-Sn and inhibits the growth of Ag9In4 during slow cooling.
