Study on the Effect of Fillers on Hygrothermal Properties of Underfill via in-Situ SEM-DIC Characterization

Underfill is a critical material in advanced packaging, widely used in flip-chip interconnection to enhance packaging reliability. Polymer systems, primarily composed of epoxy resin and silica, are the most commonly used functional composite materials for underfill. However, moisture diffusion significantly impacts the performance of epoxy resin systems, posing a threat to product reliability. Previous studies have been focused on the chip level, utilizing wet-heat aging experimental methods and corresponding characterization techniques for performance analysis. In this study, the epoxy resin bulk material was subjected to aging treatment at 121°C and 100% relative humidity using an aging test chamber. Three-point bending fatigue crack propagation experiments were conducted using a universal testing machine, and scanning electron microscopy was employed to analyze the debonding behavior of different samples. Finally, in-situ three-point bending tests were carried out to observe microscale deformations in real-time, with the use of Digital Image Correlation (DIC) to quantify strain fields at the crack tip. Ultimately, in combination with positron annihilation experiments, the impact of humid aging environments on epoxy resin composite systems was analyzed.