Reliability of ACF joint using bumpless chip after reflow process

The influence of the reflow process on the reliability of anisotropic conductive film (ACF) joints using bumpless chips was investigated. The contact resistance of the ACF joint was found to increase as the peak reflow temperature increased. The results also indicated bump height was not the controlling factor for the ACF joint reliability. During reliability test, bumpless chips proved to be unreliable owing to the inherent behavior of aluminum under a wet environment (corrosion-degradation). The moisture ingression into the ACF can lead to unstable reliability of the joint. Moreover, the ACF showed degradation in both chemical and physical properties, including modulus reduction, polymer hydrolysis, and surface swelling. In reflow soldering after temperature/humidity test, the ACF joint reliability was further deteriorated due to thermal-induced stress of different component CTE and hydroscopic swelling-induced stress of the epoxy.