Ultrasonic-assisted thermo-compression bonding method for high-performance solder anisotropic conductive film (ACF) joints

In this study, in order to improve the reliability of ACF joints in the electronic packaging with minimized mechanical damages, solder ACF bonding using ultrasonic-assisted thermo-compression (TC) bonding was demonstrated. This technology utilizes small ultrasonic vibration with TC bonding to break solder oxide layers for better wetting of solder on the electrodes in the ACF joints. Ultrasonic-assisted TC bonding was also performed with various bonding parameters in comparison with conventional TC bonding methods. Bonded solder ACF joints were investigated in terms of solder joining behavior, and reliabilities. According to the experimental results, ultrasonic-assisted TC bonded ACF joints showed approximately two times larger diameter of solder wetting area on electrodes than that of conventional TC bonded ACF joints. Moreover, when bonded to ENIG finished Cu pads, the Au contents of solder particles in the ACF joints bonded with ultrasonic-assisted TC bonding was 12 atomic % which was three times higher than those bonded with conventional TC bonding. In the unbiased autoclave test (121°C, 2atm, 100%RH), ultrasonic-assisted TC bonded ACF joints showed open circuit failure 3 times lately than those with conventional TC bonding due to good interconnection between solder particles and electrodes by sufficient solder wetting. These results mean that solder ACF bonding using ultrasonic-assisted TC bonding would be one of the solution for high reliable ACF joints in the package without mechanical damages.