Applications of Nanoindentation in the Evaluation of Mechanical Properties and Reliability of Sn-Ag-Cu Solders

摘要

This paper reports mechanical and microstructural characterization performed on the Sn- Ag-Cu alloys, which are currently considered to be the best replacement for Pb-Sn solder. In particular, nanoindentation was used to assess mechanical properties such as elastic modulus and hardness of individual constituents of Pb-free alloys (i.e., Sn-based matrix and various types of IMCs). This work is part of a research to correlate nanoindentation results to macroscopic solder performance in order to determine the relevance of nanoindentation work in evaluating solder joint reliability. Further, in order to identify the controlling deformation mechanisms at elevated temperatures, nanoindentation creep tests were employed to measure the stress exponent and activation energy. Results show that the stress exponent decreases from roughly 11 to 3 when the temperature is raised from room temperature to 84 ºC. The calculated activation energy of the solder was in the range of 153-211 kJ/mol for an applied stress of 100-200 MPa, which is higher than that from tensile creep experiments.