Advanced Modeling of Cure Shrinkage and Viscoelasticity for Warpage Prediction on Image Sensor Packaging

This paper presents a mechanical simulation of image sensor packages, with a particular emphasis on accurately modeling the cure shrinkage and viscoelasticity. Image sensors have a wide application in mobile phones, autonomous vehicles, and medical imaging. They are highly sensitive to warpage and misalignment, which can significantly degrade the image quality. The encapsulant acts as a primary barrier, protecting the sensor from external factors such as moisture and thermal mechanical stress. Accurately modeling and predicting the package warpage is crucial to ensure the optimal optical performance. Previous simulation studies on image sensor packaging often neglect cure shrinkage, leading to inaccurate warpage predictions. Cure shrinkage, a phenomenon where the material contracts during the curing process, can induce significant stress on the package and lead to warpage in addition to CTE-mismatch. This work developed a new simulation approach to incorporating cure shrinkage modeling, and it achieved a much higher degree of accuracy in predicting package warpage, as demonstrated by the close correlation between simulation results and actual warpage testing data. Furthermore, this paper studied the impact of using viscoelastic properties and compared time-dependent deformation with elastic solutions. Finally, this paper conducted comprehensive design of experiments (DOE) studies to evaluate the impact of different encapsulant materials on the susceptibility to glass cracking. The findings of this work are particularly useful for improved warpage prediction in simulation and better understanding of encapsulant properties, ultimately optimizing the package design and enhancing the reliability and longevity of electronic devices.