Delamination Evaluation Approach for Bimaterial Structure Considering Interfacial Layer

In recent years, interfacial fracture is one of the most important issues in the assessment of reliability of electronics packaging. In particular, underfill (UF) resin is used to prevent thermal fatigue of solder joints in flip chip packaging. Interfacial fracture between components/substrates and UF resin also affects the reliability of electronic devices. In general, the interfacial strength can be evaluated with the concept of interfacial fracture mechanics. However, as new materials and new processes using in the devices increase, it becomes clear that the fracture concept is difficult to evaluate the interfacial strength quantitatively. Many researches assumed that the interface is bonded perfectly. However, the interface has the micro-scale structure and the bonding may be imperfect. Specially interfaces of the resin have complicated structure. In this study, an alternative approach for evaluating the mechanical fracture of the interfacial structure of resin in electronic components was proposed. The basic mechanical behavior of the new interfacial model with imperfect bonding layer was examined by using finite element analysis. The stress field around the interfacial layer depends not only on the properties of interfacial layer but also on the micro structure of the interfacial layer. In addition, based on the experimental result of the tensile and the shearing test from the reference, the mechanical models of the interfacial structure were constructed. The conditions of delamination were examined by using FEA Furthermore, the new model and approach was confirmed quantitatively. It was found that the basic properties of the interfacial layer can be tuned to the proper values by two different delamination tests, and the new approach could show good agreement with the experimental results from the initial delaminaiton to the instability fracture process qualitatively. The simulation results were in good agreement with the experimental results.