Packaging materials influence greatly on reliability and performance of electronics components. While, materials such as molding compound protect the package from the environment; different mechanical properties of materials will inevitably introduce stress to the package. In this study, materials' viscoelastic effect on packaging stress in a MEMS sensor was studied using finite element analysis after measuring the properties of molding compound and die-attach materials in a series of stress relaxation experiments. The stress distribution, stress-time and stress-temperature relationship, were simulated under different final temperatures and cooling rates. It is found that viscoelasticity has significant effect on the packing stress, especially at higher temperature.
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