DSC investigation of the undercooling of SnAgCu solder alloys

This study investigates the undercooling of commercially available SnAgCu solder alloys by Differential Scanning Calorimetry (DSC - rate 10 K/min). The results for solder spheres of 0 260 mm (free standing, no interfacial reaction) show that Sn-based solder alloys (investigated alloys Sn99.9; SnCu0.5; SnCu0.7; SnCu1.2; SnAg3.0; SnAg4.0; SnAg3.0Cu0.5; SnAg3.0Cu1.2; SnAg4.0Cu1.2; SnAg3.8Cu0.7) solidify with significant undercooling ranging from 16.9 K to 81.7 K in the present study. It is also shown that undercooling can strongly vary from alloy to alloy and even during subsequent measurements of the same sample. Furthermore the results indicate that undercooling increases with decreasing sample size, which has to be taken into account if the interconnect size becomes smaller.