Flip chip assembly utilizing anisotropic conductive films: a feasibility study

There is a persistent effort to miniaturize, reduce costs and search for environmentally friendly alternatives in the semiconductor industry. With the many advantages of flip chip assembly technology, it is predicted to be utilized for a larger percentage of all semiconductor packaging in the future. Anisotropic conductive films (which are generally used to assemble die to glass for liquid crystal displays) are now being investigated as a replacement for traditional Pb-Sn solder bump flip chip assembly applications. In this study, the goal was to determine which parameters are critical to develop a robust and reliable assembly process of a die to an organic substrate (FR5). Design of Experiments was used to determine which process parameters were critical in meeting reliability requirements. Reliability testing included -55C to 125C liquid-liquid thermal shock and autoclave (121C 1 atm. Pressure). Additional parts were also assembled and subjected to multiple Sn-Pb and Sn-Ag reflow profiles to study the effect of BGA solder reflow on the ACF film. The results show that Ni bump thickness and bonding pressure are critical parameters (for assembly on organic substrates) in maintaining a robust product through extensive reliability testing. Experiments have shown that anisotropic conductive films may be a viable option as a cost effective, lead free flip chip assembly alternative