Room temperature ACF bonding process using ultrasonic vibration for chip-on-board and flex-on-board applications

In this study, a novel anisotropic conductive film (ACF) bonding process using ultrasonic vibration was investigated in chip-on-board (COB) and flex-on-board (FOB) applications. The ACF temperature increased as the U/S power increased and the bonding pressure decreased. The ACF temperature was successfully controlled by adjusting both U/S power and bonding pressure. The optimized U/S bonding time was 3 sec at room temperature. The significant meaning of this result is that the ACF bonding process can be remarkably improved by U/S bonding compared with conventional 15 sec T/C bonding at 190degC. Using the optimized U/S bonding parameters, the ACF interconnects showed similar bonding performances as T/C bonding in terms of the daisy-chain resistance and the adhesion strength. The FTIR (Fourier transformation infrared spectroscopy) analysis showed that the cure degree of adhesive resin was achieved 90% at 3 sec. In the reliability tests, the U/S bonded ACF interconnects showed no significant change in electrical resistances during 85degC / 85% RH test and 125degC high temperature storage test for 1000 hours and -55degC -125degC thermal cycling test for 1000 cycles.