Fracture Modeling and Characterization of Si/Underfill/Substrate Interface Adhesion in 3D Packaging

In recent years, underfill technology has been playing an increasingly important role in advanced packaging, and the associated reliability issues of bonding structures have become more significant. Particularly, the well-formed bonding interface formed by the underfill adhesive in the packaging structure determines the ability to resist cracking and delamination, which is crucial for ensuring the reliability of electronic packaging devices. Currently, most research has focused on various bonding interfaces of underfill in FC packaging. However, with the rapid development and application of advanced packaging technologies such as 2.5D and 3D, the failure issues exposed by underfill in their structures have become more prominent. In this study, a commercial underfill material was used to prepare a simplified Si/underfill/substrate bonding structure, designed to mimic the widely adopted structure of silicon interposer/underfill adhesive/substrate in actual 3D packaging. A combined experimental and finite element modeling method was proposed to determine the bonding strength of the Si/underfill/substrate structure. This method conducts interface analysis based on the theory of fracture mechanics, conducts single cantilever beam test and lap shear test on the two main failure modes of model I and model II, and then uses the test results as simulation parameters. Through iterative simulation, a cohesive zone model (CZM) characterizing crack initiation and propagation was established. In summary, the method of establishing the CZM model can not only evaluate the delamination risk of the Si/underfill/substrate interface in 3D packaging but also provide a convenient and cost-effective approach for analyzing other similar interface delamination issues.