Ultrasonic bonding of die attach film (DAF)-laminated thin silicon dies on glass substrates at room temperature

The effect of introducing ultrasonic energy to reduce the bonding temperature and time as well as the void formation in state-of-the-art thermocompression bonding of die attach film (DAF)-laminated thin silicon dies on glass substrates is reported in this paper. Process studies are conducted using an in-house automated thermosonic bonding equipment equipped with a 40 kHz ultrasonic transducer. The specimens bonded by the thermosonic process are compared with the ones bonded by the thermocompression process at various combinations of bonding temperature, time, and pressure as well as ultrasonic power of the transducer in terms of the percentage of void formation. The voids formed at the interface between the DAF and the glass substrate are examined using a digital optical microscopy technique. The results show that the thermosonic process of DAF bonding can effectively reduce the bonding temperature and time as required by the thermocompression process, besides obtaining good bondability between the DAF and the glass substrate. The bonding time can be reduced to 0.3 s for bonding temperature at or above 60 °C and with an ultrasonic power of 100 W. Ultrasonic bonding at room temperature can be achieved with a bonding time of 2.5 s and an ultrasonic power of 150 W.