A modified Qian-Liu constitutive model based on advanced packaging underfill materials

—The high integration and multifunctionality of microsystem packaging have led to a gradual reduction in packaging size, bringing changes in materials, structures, and processes. This has resulted in numerous issues related to structural reliability and signal integrity. To address the problems of stress concentration during chip packaging, underfill materials are typically introduced beneath the chip. Therefore, the appropriate underfill selection significantly impacts chip reliability. In this work, a modified Qian-Liu constitutive model is proposed to describe the viscoplastic deformation of underfill. The new model accurately predicted the overall trend of stress-strain behavior for the temperature range from 298K to 398K and the strain rate range from 0.0001s−1 to 0.00ls-1. Constitutive parameters of the underfill over a wide temperature range based on the modified Qian-Liu model were obtained. A comparison between the experiment and simulation verified that the modified Qian-Liu model reasonably simulated the viscoplastic stress-strain relationships for underfill materials.