Measurement of mechanical properties of Sn-Ag-Cu series lead-free solder alloy by using micro-indentation

Sn-Ag-Cu series alloy is considered as the lead-free alternative to lead-tin alloys. A new method was introduced to measure the mechanical properties, i.e. modulus of elasticity and creep strain rate sensitivity by using depth-sensing micro-indentation with the influence of loading rates on load—displacement (Fh) relationship. The resulting indentation Fh curves are loading-rate-dependent and have varying creep penetration depths during the same hold time. The derived modulus of elasticity values with Oliver-Pharr method from unloading curves are loading rate-independent. The creep strain rate sensitivity can be determined from the relationship between the creep hardness and creep strain rate by the definition of “work of indentation”. Also, micro-indentation tests on two Sn-~3.5 Ag-0.75Cu and Sn-3.0Ag-0.5Cu lead-free solder alloys show a slight influence of alloy composition on mechanical properties for Sn-Ag-Cu series solder.