Interfacial thermal stresses in solder joints of leadless chip resistors

A novel two-dimensional analytical model has been developed for the interfacial thermal stresses in the solder joints of a leadless chip resistor (LCR) assembly under both plane stress and plane strain conditions. Both global and local expansivity mismatches are incorporated into the model. Interfacial thermal stresses are approximated using elementary strength of materials theory. Governing differential equations are linearized through a finite difference discretization procedure. The conditions of zero shear stress at the free edges and self-equilibrated peel stresses are met. The model is more accurate than existing ones, is mathematically straightforward, and can be extended to include inelastic behavior. The results are compared with available data in the literature and finite element analysis, and a geometry optimization is performed for a sample LCR as an example of the use of the model.