Flip chip assembly utilizing anisotropic conductive films: afeasibility study

摘要

There is a persistent effort to miniaturize, reduce costs andsearch for environmentally friendly alternatives in the semiconductorindustry. With the many advantages of flip chip assembly technology, itis predicted to be utilized for a larger percentage of all semiconductorpackaging in the future. Anisotropic conductive films (which aregenerally used to assemble die to glass for liquid crystal displays) arenow being investigated as a replacement for traditional Pb-Sn solderbump flip chip assembly applications. In this study, the goal was todetermine which parameters are critical to develop a robust and reliableassembly process of a die to an organic substrate (FR5). Design ofExperiments was used to determine which process parameters were criticalin meeting reliability requirements. Reliability testing included -55Cto 125C liquid-liquid thermal shock and autoclave (121C 1 atm.Pressure). Additional parts were also assembled and subjected tomultiple Sn-Pb and Sn-Ag reflow profiles to study the effect of BGAsolder reflow on the ACF film. The results show that Ni bump thicknessand bonding pressure are critical parameters (for assembly on organicsubstrates) in maintaining a robust product through extensivereliability testing. Experiments have shown that anisotropic conductivefilms may be a viable option as a cost effective, lead free flip chipassembly alternative