Damage evolution in lead-free solder joints: Industrial setting, computational mechanics and data perspective
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The EU’s RoHS (Restriction of Hazardous Substances) directive mandates lead-free soldering for most electronics. Industry would highly benefit from a concurrent experimental and simulation approach in the development and optimisation of new solder materials and processes, significantly reducing time to market. Material complexity, i.e. intermetallic phases, high local gradients of temperature, stress and composition, varying failure modes [1] highly sensitive on stress [2], temperature and local impurity contents [3] appear. A high entrance barrier to the topic is imposed by the generally lacking consensus on a standardised, advanced numerical full field modeling framework [4], as well as standardized microstructural and thermodynamic data. Recently, a novel numerical methodology for the mathematical modeling of phase transformations has been applied to lead free solder joints [4], where solving for rate-dependent variables, yields a stabilized solution of an otherwise unstable system of equations, which commonly is overcome by using gradient regularization. While the specific variational form used to solve the equations has been previously employed e.g., to stabilize solutions of the Laplace equation, its application to diffusion and diffusional phase transformations is a novelty. In particular, it enables to directly use the convex envelope of the Gibbs potential from thermodynamic data. This way, the influence of stresses (externally applied as well as originating in local phase-transformations) is shown to be significant in simulations, which is why they cannot be neglected for lifetime or reliability models as required by the industry.
