Evaluation of the primary and secondary creep of SnPb solder joint using a modified grooved-lap test specimen

The time and temperature dependant creep deformation of solder alloys has to be studied to describe material characteristics and failure behaviour, in order to use it for lifetime evaluation by FE-simulations. It is often found in the literature that the material behaviour of eutectic SnPb solder is described considering only secondary creep. As this paper shows, primary creep may not be neglected because of its appearance in the performed characterisation tests and application examples. To study the creep behaviour, the grooved lap geometry described by Reinikainen was used and additionally modified to see crack and cavities in the solder joint using an SAM (scanning acoustic microscope). The test specimen was cyclically loaded for different stress levels and temperatures. Primary and secondary creep was observable under conditions of load reversal. A combined creep law using primary and secondary creep is presented and an example is shown to highlight the relevance of the primary creep.