Effects of Forming Processes on the Microstructure and Solderability of Sn-3.5Ag Eutectic Solder Ribbons as well as the Mechanical Properties of Solder Joints

Two kinds of Sn-3.5Ag eutectic solder ribbons of 0.13 mm thickness were prepared by a casting–rolling process and a rapid solidification process. The microstructure, phase constitution, melting characteristics, wetting behavior and soldering strength were compared using optical microscopy, scanning electron microscopy, x-ray diffraction, energy dispersive spectroscopy, differential scanning calorimetry and a MTS ceramic testing system. The results show that the microstructure of rapidly solidified solder is finer and more uniform, and the eutectic structure has a higher solid solubility and more homogeneous distribution of Ag in a Sn matrix. The solidus and liquidus temperature decreased, resulting in a 3.3% reduction of pasty range. In addition, the wettability and shear strength of the solder joints increased by 13.2% and 7.9%, respectively.