Curing and bonding behaviors of anisotropic conductive films (ACFs) by ultrasonic vibration for flip chip interconnection

In this study, the curing and bonding behaviors of ACFs by ultrasonic vibration for flip chip interconnection were investigated using a 40 kHz ultrasonic bonder with longitudinal vibration. In-situ temperature of the ACF layer during thermosonic (TS) bonding was measured to investigate the effects of substrate materials and substrate temperature. Curing of the ACFs by ultrasonic vibration was investigated by dynamic scanning calorimetry (DSC) analysis in comparison with isothermal cure. Die adhesion strength of TS bonded specimens was compared with that of thermo-compression (TC) bonded specimens. The temperature of the ACF layer during TS bonding was significantly affected not by substrate temperature but by substrate materials. The temperature of the ACF layer increased up to 300degC within 2 seconds on FR-4 substrates but 250 degC within 4 seconds on glass substrates at room temperature. ACFs were fully cured within 3 by ultrasonic vibration, because ACF temperature reached at 300 degC within 3 seconds. Die adhesion strengths of TS bonded specimens were as high as those of TC bonded specimens both on FR-4 and glass substrates. As a summary, TS bonding of ACF will significantly reduce the ACF bonding times at several seconds, and also make the bonding possible at room temperature compared with tens of seconds bonding times and more than 180degC bonding temperature of TC bonding