Anisotropically conductive adhesive flip-chip bonding on rigid and flexible printed circuit substrates

A systematic experiment on flip-chip bonding assembly using an anisotropically conductive adhesive (ACA) has been carried out. The assembled modules have been characterized by a number of environmental tests, including aging, constant humidity, temperature cycling, humidity cycling, shear, vibration, and shock testing. The results indicate that under optimum process conditions, high quality and high reliability joints can be achieved. Conduction failure mechanisms have been investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The analysis shows that failure is dependent on competition between driving factors; thermal stress, elastic stress, expansion due to moisture absorption on one side, and the resistant factor, i.e., interatomic force. Variation of the filler size in the ACA, configurations of chips and boards, as well as bonding pressure and its distribution are among the most important factors that control the bonding quality and reliability.