A study for the new-type ACF applications of FCOF assembly

Due to the environmental protection issues and regulations, a lot of electronic material suppliers try to search for the replacement materials which include the lead-free solder joints and the anisotropic conductive films (ACFs). ACF is widely used in high quality, excellent signal interconnection and fine pitch products. Nevertheless, during the fast flow and curing process of the electronic material, the risk of voiding may be increased. This study focuses on the characteristics and phenomena of a new-type ACF on the outer lead bonding (OLB) for flip chip on flex substrate (FCOF) assembly. Firstly, the thermal response and curing capability of the new-type ACF is investigated by the experiment. And the numerical simulation is used by computer aided engineering (CAE) that shows the heating effect of components on the bonding process. Both the simulated and experimental results can obtain the similar thermal behaviors. For the reliability assessment of the new-type ACF, the experiment procedures are adjusted three parameters of temperature, pressure and time under the bonding process. It can be easily discovered that the delaminations or cracks is caused by a lower compliance behavior of the interfaces between bumps on the polyimide (PI) substrate and indium tin oxides (ITOs) on the glass substrate. In order to evaluate the adhesive strength of ACF through the thermal loading, the strength of FCOF assembly is measured by a 90-degree peel test and is verified by the CAE simulation. In this study, the minimum peel strength of the new-type ACF has to be greater than 400 g/cm in order to satisfy the specification. Then, a stripped meshed model is simulated to understand the fracture growth between each interface under a constant speed of 8mm/sec. It can be found that the initial creak starts from the ACF-glass substrate interface and then propagates to the ITO. Finally, the swelling phenomenon of the new-type ACF is investigated. It shows that the swelling will not affect the structure of components and the reliability assessment is good.