Stress evolution in an encapsulated MEMS package due to viscoelasticity of packaging materials

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.