The Effect on Bonding Process and Reliability for ACF Applications

Due to the environmental protection issue and regulation, many material suppliers try to find the replacing material. Now, the most popular technologies which can replace the classical Pb/Sn material are lead-free joints and anisotropic conductive films (ACFs). Because conductive particles play an influential role in component, this paper is going to investigate the effects that conductive particles at different spots in package. The CAE software, ANSYS, is used to examine the bonding and reliability assessment of ACF in the fine pitch chip on flex package with a-quarter model under various bonding process parameters. First of all, Taguchi method is used to study the bonding processes and associated parameters. This research also considers the noise factors which generate disturbing function in orthogonal array and discusses the conductive particles which have more distortion in package. After getting the analysis of variance, the thermo-mechanical behaviors of the optimized package undergoes the temperature test. According to the specification of moisture soak, using the moist sensitivity level 1, which is analyzes the phenomenon of moisture absorbed. The package consists of the multi-material components. As the thermo-mechanical status of the package results from the different coefficient of thermal expansion with the loading variations, it is obvious that von Mises in the devices happens between bump and pad, which may cause crack initiation. Taguchi method with noise factors can get more suitable parameters and arrangement of conductive particles, that is, inside one creates more stress than the other. Therefore, the thermo-mechanical behaviors of the optimized package show that the maximum stress and warpage still happen at the interface between the bump-ACF and the ACF-pad in the corner of package at a higher temperature. The simulation technique of heat conduction can be applied to the analysis of moist absorbability as well. Results under moist sensitivity level 1 show that the moisture propagates slowly from outer surface to the inner package.