Application of Underfill for Flip-Chip Package Using Ultrasonic Bonding

概要

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In this study, the reliability of flip-chip (FC) packages with various underfills using ultrasonic bonding was evaluated in temperature and humidity (TH) tests. Fatigue cracks began at the interface between the Au bumps and glass substrate and then propagated through the interface with increasing dwell time in the TH test. The initial electrical resistance of Au bumps with lower viscosity underfill was lower than that of Au bumps with higher viscosity underfill. Entrapped underfill between the Au bumps and glass substrate or void formation between the Au bumps in FC packages was caused by high viscosity of the underfill. As the dwell time of the TH test increased, the electrical resistance of the FC packages increased. The fatigue life of an FC package with underfill that has a higher glass transition temperature ($T_{\text{g}}$) and lower coefficient of thermal expansion (CTE) value was higher than that of an FC package with underfill with lower $T_{\text{g}}$ and a higher CTE value. Therefore, the properties of underfill affect the fatigue life of FC packages with underfill using ultrasonic bonding.
2008-05-25