Experimental Analysis of Compressive Stresses in ACF Flip Chip Joint and Its Influence on ACF Joint Reliability

This paper presents the mechanical contribution of shrinkage stress in a bonding process to electrical conduction establishment and reliability of ACF joint. The conduction establishment and reliability of ACF joint strongly depend on joint clamping force related with the thermal and mechanical properties of ACF. Therefore, it is important to understand the effect of ACF shrinkage stresses on the conduction establishment and reliability. In this study, thermal and mechanical properties of ACF materials were investigated during and after thermal reaction. The important mechanical mechanism of ACF conduction for good bonding quality and reliability is the joint clamping force developed during curing and cooling-down process of ACFs. Based on thermo-mechanical properties involved in ACF thermal reaction, the build-up behavior of thermally induced shrinkage stress during curing and cooling-down processes of ACF materials was experimentally investigated. It was experimentally shown that the shrinkage stresses of ACF materials are strongly dependent on material properties such as modulus, CTE and T_g. Moreover, it was evident that in temperature aging test, ACF joint reliability was affected by compressive stress. These results indicate that shrinkage stress, developed by the thermal reaction of ACFs, is the important parameter to the electrical conduction establishment and reliability of interconnects using ACF material.