Development a hybrid tin-whisker growth model

The international drive to lead-free electronics has resulted in the potential use of tin as an economical alternative. Tin-based solder products and finishes are a risk in supply-chain due to the threat of component failure due to tin whiskering (filament-like growths associated with tin material stresses). Tin whiskers are related to, identified, or have been suspect in the failures associated with several RoHS compliant electronic components and medical devices. The current work proposes a hybrid FEM/experimental method to develop an improved understanding of the mechanisms of tin whisker growth.

In the realm of semiconductor failure analysis the “metaprocess” loop developed by the Electronic Device Failure Analysis Society (EDFAS) has been a proven technique for expediting the generation of new hypothesis or models of device failure. Within the EDFAS model, the “hybrid” process replaces the customary “measurement” step with a FEM multiphysics time-dependent calculation whose boundary conditions are set by experimental measurements. The method is unique in that experiments are not exclusively for an understanding of mitigation success, but rather for “steering” the FEM code through a step-wise assessment of (proposed) tin whisker growth models and related thermodynamic properties.

This technique aids in the abstraction of data for model development in three ways: (1) A hybrid simulation overcomes an otherwise narrowly defined FEM calculation centered on a specific numerical objective. (2) A tin whisker growth model expressing thermodynamic properties more easily unifies measured, observed, and computed growth factors. (3) Changes in specific thermodynamic property trends can be compared against existing results from other whisker growth research groups.