Optical MEMS die-attach warpage analysis and mitigation via thermoelastic modeling and in-situ micro-Raman spectroscopy characterization

Abstract

Optical micro-electromechanical systems (MEMS) demand exceptional precision, yet warpage during the die attach process on printed circuit boards can compromise performance. Here, a three-dimensional thermoelastic analytical model has been developed based on Fourier heat conduction and supported beam theory. This model facilitates the in-situ calibration of solder parameters via confocal micro-Raman spectroscopy, ensuring that the simulated dynamic evolution of warpage during soldering aligns closely with digital image correlation experiments. The results show consistence with Finite Element Method with error less than 1 % and time saving more than 60 %. Orthogonal experimental analysis further reveals that substrate thickness and thermal expansion coefficient variations are the primary factors affecting warpage, while chip area has a negligible role. Given the practical challenges in reducing substrate thickness, a stress-balancing strategy incorporating an additional transition layer is proposed, which is effectively validated with a high-resolution three-dimensional profilometer. This work provides valuable insights into the predictive modeling and warpage behavior characterization, directly supporting improved mitigation strategies in the die attach process.