Interfacial Shear and Peel Stresses in Multilayered Thin Stacks Subjected to Uniform Thermal Loading

An analytical approach has been developed to evaluate the interfacial shear and peel stresses in multilayered thin stacks subjected to uniform temperature variation. The approach, which is based on an extension of Suhir’s bimetal thermostat model, provides a system of coupled linear second order differential equations used in solving for the interfacial stresses. Once these stresses have been determined, the normal stress in each layer and the deflection of the stack can be readily obtained. Two numerical examples are used to demonstrate the capability of the approach. The first example deals with a five-layered symmetric double-shear solder joint. The results are compared to a nonsymmetric three-layered solder joint to study the effect of bending and the interactions of material properties. One of the interesting features observed is that the maximum interfacial shear stress does not necessarily occur at the edge. The other numerical example is a four-layered transistor stack mounted on a substrate. The structural behavior is analyzed, and the effect of geometric dimension is examined. The present approach is shown to provide more accurate results than those of others based on the same assumptions. In addition, applications of the approach to more general stack configurations are also discussed.