Materials behaviour and intermetallics characteristics in the reaction between SnAgCu and Sn-Pb solder alloys

This paper illustrates the application of thermodynamic modelling techniques that are capable of simulating and predicting a range of interacting physical phenomena associated with the thermodynamic behaviour of multicomponent Sn-Pb/Pb-free solders in relation to solder joint manufacture and long term reliability. The paper compares theoretical calculations with experimental data, to identify the metallurgical mechanisms with regard to the rework or repair that may be encountered in the transition period from Sn-Pb to Pb-free soldering. Thermodynamic calculations have been carried out to study the material behaviour and possible formation of intermetallic precipitates during the reaction between Sn-Pb and Sn-Ag-Cu Pb-free alloys. Two Sn-Ag-Cu alloys that are relevant to current industrial interests, namely Sn-3.9Ag-0.6Cu and Sn-3.0Ag-0.5Cu were reacted with different contamination levels of eutectic Sn-37Pb solder. The variables related to the materials and processes, such as composition, temperature and cooling rate, are the primary concerns with respect to resultant microstructures, which have also been studied experimentally using optical and scanning electron microscopy (SEM). The results from this work provide guidance as to the consequence for microstructural evolution and hence mechanical integrity when small amounts of Pb exist in Pb-free alloys.