Effects of Resin and Curing Agents on Residual Stress in Underfill Material and Wafer-level Warpage

Underfill material (UF) is critical for ensuring the reliability of advanced packaging structures. Therefore, maintaining its mechanical stability and minimizing residual stress induced by curing shrinkage are essential requirements for developing advanced UF. This study examines how different resin matrices and varying hardener ratios affect UF properties and ultimately lead to wafer warpage. The AFG-90 resin with high crosslinking density forms a rigid network, resulting in increased storage modulus, decreased coefficient of thermal expansion (CTE), and elevated residual stress/deformation. A higher proportion of hardeners further increases the crosslinking density, thereby amplifying the stress effects. The dependence of residual stress on UF modulus and CTE was verified through finite element simulations. By optimizing the composition ratio, low-stress UF systems can effectively mitigate deformation and reduce packaging failures, providing a theoretical basis for material design.