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 degrees C, 100%RH and 2 atm. The results showed that the joint resistance of the ACE flip chip increased during the tests and nearly 25% of the joints were found open after 168 h' 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. (C) 2013 Elsevier B.V. All rights reserved.