Adhesion strength and contact resistance of flip chip on flex packages - Effect of curing degree of anisotropic conductive film

The use of anisotropic conductive adhesives film (ACF) as an interconnect materials for flip-chip joining technique is increasingly becoming a vital part of the electronics industry. Therefore, the performances of the ACF joint turn into an important issue and depend mostly on the curing condition of the ACF matrix. ACF is a thermosetting epoxy matrix impregnated with small amount of electrically conductive particles. During component assembly, the epoxy resin is cured to provide mechanical connection and the conducting medium provides electrical connection in the z-direction. Therefore, the cure process is critical to develop the ultimate electrical and mechanical properties of ACF. The purpose of the present work is to investigate optimum curing conditions to achieve the best performance of ACF joints. Differential scanning calorimeter was used to measure the curing degree. Adhesion strength was evaluated by 90° peeling test. The contact resistance has also been studied as a function of bonding temperature and curing degree. Results show a strong dependence of curing condition on the electrical and mechanical performances. Adhesion strength increases exponentially with the curing degree. Whereas the contact resistance decreases with the curing degree and achieve the minimum value at 87% of curing. Co-relation of the curing degree of the ACF was also studied through the detailed investigation of the fracture surfaces under scanning electron microscopy. © 2003 Elsevier Ltd. All rights reserved.