Material characterization of organic packaging materials to increase the accuracy of FEM based stress analysis

Organic packaging materials gain a steady increasing importance for electronics packaging assemblies. They are used in various ways in substrate materials, adhesives, encapsulations, underfills and many more. This paper outlines the importance of thermo-mechanical characterization of these polymeric packaging materials to improve the accuracy of Finite Element Modeling for advanced reliability analysis of electronics packaging solutions. Therefore the effects of including temperature-and time dependent mechanical material properties of a PPS molding compound were investigated. This molding compound should be used as a coupling element to decrease the occurring stresses in an array of solder connections between substrate and package. The setup was analyzed by FEM (Finite Element Modeling). For the material characterization a DMA 2980 equipment was utilized to determine the time- and temperature dependent elongation modulus of the molding compound material. A description of the measurement setup and parameter selection is given. Subsequently the measurement results are presented. To use this measurement results in a material model for time dependent elongation modulus the results needed to be fitted to a Prony series model which allows implementing this complex material behavior in the FEM simulation software Ansysreg. Additional the WLF (Williams-Landel-Ferry) shift function was determined and implemented to add the temperature effect to the viscoelastic material data used for simulation. For the stress analysis the package setup was implemented as geometric model of the real structure and the loading conditions were defined. The simulations showed that there are significant differences in the occurring stress levels in the setup. For higher temperatures the stress levels were decreased due to stress relaxation in the polymer.