Experimental characterization and finite element analysis of thermo-mechanical stress in flip-chip- and wirebond-assemblies on flexible and injection molded thermoplastic substrates

In this paper, research activities on the reliability for bare die connections on molded interconnected devices (MID) and flexible substrates are presented. The results were achieved by experimental, thermo-mechanical stress characterization combined with finite element analysis (FEA) of the assembly during application specific environmental conditions. Aim of the work is to determine the influence of thermo-mechanical stress on different assembly variants. Therefore, four different assemblies are examined each on four different substrates: Aluminum wire bonded chip, flip-chip with 200 μm SAC305 solder balls for reflow soldering, flip-chip with gold stud bumps for an isotropic conductive adhesive configuration and flip-chip with gold stud bumps for a non-conductive adhesive configuration. For flip-chip assemblies an additional underfill was used to mechanically strengthen the connection between chip and substrate. To gain data from the real assemblies, aspecial stress detection chip with boron doped solid state resistors has been adapted for the requirements of the research project. The matching of numerical analysis and real assembly was done by measuring the mechanical stress in the chip during thermal cycling of the assemblies. The real time stress data of the piezo resistive resistors were recorded and compared to the thermo-mechanical FEA results.