Failure probability of wire bonding packages

This paper presents a methodology/model for elastro-plastic analysis of the wire bonding packages. The methodology is based on finite element method for rate sensitive materials and applicable to very large deformation processes. Ultrasonic power is simulated as displacement boundary condition. Stress induced by the mismatch of the coefficient of thermal expansion (CTE) in the system because of temperature increase due to application of the ultrasonic or the reflow process is considered. The effect of temperature increase on material property is also accounted for. Nonlinear spring elements are adopted to simulate the gradual formation of intermetallic bonding layer between the ball and the electric pad. With these spring elements, the effect of stress and strain relaxation of the ball in the subsequent procedures such as reflow process is taken into account. The mechanical behavior of the silicon chip during the wire bonding with the ultrasonic irradiation and reflow process is thus revealed. Failure probability with reference to the stress distribution is discussed. The developed FE methodology is simple but effective to evaluate the failure probability of wire-bonding packages.