Effects of moisture absorption on anisotropic conductive films interconnection for flip chip on flex applications

This paper reports the investigations into the moisture induced failures in Flip-Chip-on-Flex interconnections using Anisotropic Conductive Films (ACFs). Both experimental and modelling methods were applied. In the experiments, the joint resistance was used as a quality indicator and was measured continuously during the autoclave test. The test condition was set as 121^oC, 100%RH and 2atm. The results showed that the joint resistance of the ACF flip chip increased during the tests and nearly 25% of the joints were found open after 168h' testing. Visible conduction gaps between the adhesive and substrate pads were observed. Cracks at the adhesive/flex interface were also found. In order to have a better understanding of the experimental results, 3D Finite Element (FE) models of the ACF assembly were constructed and a macro-micro modelling technique was used to overcome the difficulty caused by the multi-length scale in the ACF assembly. The moisture diffusion and moisture-induced stresses in the ACF flip chip during the autoclave test were predicted. Modelling results are consistent with the findings in the experimental work.