Indium Addition on Intermetallic Compound Evolution in Tin-Silver Solder Bump

摘要

The formation of large Ag_3Sn 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 Ag_3Sn. 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 30min 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 Ag_3Sn plate is substituted by Ag_9In_4 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 Ag_9In_4 during slow cooling.