Finite element (FE) simulations represent a useful tool to evaluate the thermomechanical behaviour of electronic packages. However, the use of the FE-method generates special difficulties, with particular regard to the proper constitutive modelling of materials used in the assembly. One more general problem in the numerical investigations of encapsulated silicon chips is the occurrence of interfaces between the dissimilar materials. Due to the assumption of sharp interface edges and interface crack tips, stress singularities arise which might be accounted for only approximately in the FE-calculation. The paper intends to show solutions of these simulation difficulties, also by means of materials testing. The complex material behaviour is discussed for different filled epoxy materials, with particular regard to the influence of filler content. A new solution method for the interfacial edge problem is briefly introduced. As an example, the pull strength test is used and the asymptotic solution for an interface edge is presented.
