Recent Advances in Performance-Driven Multiscale Strategies for Epoxy-Based Underfill Materials for Advanced Packaging

The rapid evolution of advanced packaging toward high-density, high-power, and three-dimensional heterogeneous integration has placed increasingly stringent demands on package reliability, particularly because of the thermal expansion mismatch and associated thermomechanical stresses between silicon dies and substrates. Owing to their favorable combination of properties and highly tunable formulation chemistry, epoxy resins remain the predominant matrix materials for underfill applications. However, the design paradigm of epoxy-based underfills is shifting from the optimization of individual thermomechanical properties toward the coordinated regulation of thermal, rheological, mechanical, and reliability-related characteristics. This review summarizes recent advances in epoxy-based underfill materials from the perspectives of thermal management, rheological optimization, mechanical reinforcement, and reliability enhancement, with particular emphasis on the roles of filler engineering, resin and interfacial design, and curing-system regulation. The intrinsic coupling and trade-offs among different performance parameters are also discussed. Furthermore, emerging directions for underfill materials in advanced packaging are outlined, including multiscale structure–property relationships, reliability prediction, and intelligent formulation design. This review aims to provide insights into the synergistic design and practical implementation of high-performance epoxy-based underfill materials for next-generation electronic packaging.