Validation and Optimization of Calculated Stress Fields in Double-Mold Optoelectronics Sensor Packaging

Thermomechanical modeling of a new double-overmolded optical sensor package, comprising a highly filled, as well as an unfilled, strongly thermally expanding transfer molding compound, is presented. Materials' characterization of the polymers using thermal, thermomechanical, dynamic, and optical correlation methods was used to set up finite element models of the three major steps in the assembly packaging process. The results of the simulation were validated by in-plane stress determination using a piezoresistive integrated circuit measured at various temperatures. In addition, the overall package substrate warpage was optically characterized while loading the sample on a hot plate. Agreement between the measurement and the simulation was only found when the stress-free state of the polymers was set to be at the curing-onset temperature. The results obtained are compared with different levels of complexity on materials' characterization and constitutive modeling and could finally be used for sensitivity analysis of the sensor package design. A thicker and more compliant transparent molding compound in this package was found to reduce the stresses that could cause delamination.