Influence of Cooling Rate and Composition on the Solidification of SnAgCu Solders

This study points out the influence of cooling rate and solders composition on the microstructure of bulk SnAgCu. Therefore the alloys SnAg3.8Cu0.7, SnAg3.0Cu0.5 and SnAg3.5Cu0.4 were solidified with different cooling rates from 0.35 K/min to 37.4 K/min. During these experiments the temperature of the solder was measured. Changes in microstructure were investigated after thermal storage at 125degC, for 0.05 h, 0.5 h, 5 h, 50 h and 500 h. In an additional experiment a temperature gradient was generated inside different solder samples during solidification. The cross sections of these bulk samples indicate influence and dependence on phase growth, caused by this directed solidification. The chosen alloys, SnAg3.0Cu0.5, SnAg3.0Cu1.5 and SnAg3.0Cu0.5Au0.14 show effects on microstructure, caused by impurities like Au and Cu, which can solute from the PCB metallization during reflow. Another experiment shows the potential and the advantages of a new developed method for temperature measurements during the reflow process