Computer based thermo-mechanical design and performance optimization are in widespread use and are mainly based on finite-element (FE-) analyses. The theoretical investigations of stresses within polymeric material compounds induced by environemtnal conditions, especially temperature changes, require both the characterization of materials properties and materials interface properties. Measurement results on typical commercially available electronic polymers are reported, which have been investigated by DMA and TMA measurements as well as tensile tests. Isothermal relaxation tests were performed on tensile specimen to study the viscoelastic material behavior at diferent temperatures. Furthermore, a non-isothermal relaxation experiment has been applied to selected encapsulants for verification of the elastic and viscoelastic constitutive models, which are based on the isothermal tests. In addition to the constitutive description, the evaluation of interfacial stress concentrations is one main problem of FE-analyses on polymeric material compounds. The stress state at interfacial edges is shown to be strongly localized as has to be expected from the often singular elastic solution at an interface edge, which is briefly discussed. Finally, reliability analyses results on flip-chip assemblies by a combined numerical and experimental approach are presented.
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