The Dependence of Composition, Cooling Rate and Size on the Solidification Behaviour of SnAgCu Solders

The scope of this study is to investigate the influences on the solidification of the micro structure of SnAgCu solders. It will be shown that the solidification process depends on solder composition, specimen size and manufacturing conditions. The influence of solder composition has been investigated on bulk solder ingots by varying the Ag content from 3.0 wt% to 3.8 wt% and the Cu content from 0.4 wt% to 1.5 wt%. The influence of an additional Au content was investigated on a SnAg3.0Cu0.5Au0.14 solder. Solidification experiments with different cooling rates from 0.006 K/s to 0.6 K/s have been carried on bulk solder ingots (length 23 mm; Oslash 7 mm) of the alloys SnAg3.0Cu0.5, SnAg3.8Cu0.7 and SnAg3.5Cu0.4. The results will point out the influence of cooling gradients on the microstructure. In order to compare the microstructure of these large specimen with real solder joints, solidification experiments with cooling rates from 0.33 K/s to 10.9 K/s have been carried out on SnAg3.0Cu0.5 solder balls with four different sizes (Oslash 130 mum, Oslash 270 mum, Oslash 590 mum and 0 1100 mum). Phase sizes and shapes as well as grain orientations have been investigated and compared. Experiments on directed solidification have been carried out in order to investigate the dendritic growth of beta-Sn dendrites. For that purpose a temperature gradient was generated inside the solder during solidification.