Importance of test parameters, specimen type and use configuration on the identification of Sn/Ag solder behaviour laws

In this paper, solder bump interconnections based on a Tin brazing process are studied under the angle of their capacity to resist to repeated thermomechanical loading. Indeed, understanding and modelling nonlinear behaviour is one of the most important milestones in the process of assessing solder reliability. However, the identification of soldering behavioural laws is highly dependent on the context and in particular on the nature of the specimen, the processes used to manufacture it as well as its utilization. This gave rise to a large number of models for the description of the creep in solder materials. Within this framework, the article aims first at proposing a state of the art on the most relevant models describing the nonlinear time dependent behaviour of this kind of solder alloy and, in particular, the different works that have addressed the modelling of the behaviour of Sn/Ag specimens. Due to the diversity of existing models, a methodology is then proposed to match analytical models and experimental data. It is shown that the results depend on the experimental setup and on the temperature used for the tests. Shear relaxation tests are used to identify primary and secondary creep. The results are discussed with respect to models and range of temperature. Based on the previous developments, an adaptation of the laws found in the literature is proposed to describe the behaviour of a Sn/Ag3.5 wire bond solder used in an IGBT rail traction module. The outcomes are experimentally validated.