Effect of Pitch Factor on Reliability of Interconnects Using Anisotropic Conductive Films: An Initial Study

This paper presents initial results in the investigation of the correlation between reduced pitches and reliability of interconnects using anisotropic conductive film (ACF). ACF interconnects were characterized with focus on curing temperature of adhesives and bond pressure. Bonded samples were evaluated by four-point electrical resistance measurement. Samples for further investigation were fabricated with selected parameters from initial characterization. Insulation resistance between ACF interconnects were then measured to determine the short circuit rate of samples with different pitches. The ACF used in this study was a 20 µm thick single layer ACF filled with 5 µm diameter conductive particles. Silicon based test chips and substrates, with interconnect pitch ranging from 110 µm to 200 µm have been designed to study the effect of pitch on reliability of the ACF interconnects. Characterization results showed that sufficient interconnect resistance could be obtained with bond pressure ranging from 100 to 140 MPa, while bond temperature was 180 oC. Insulation resistance between ACF joints in two separate daisy chains was sufficiently high (approximately 1 GO) and independent of pitch factor. This initial study has verified the feasibility of reduced pitch down to 110 µm for ACF interconnects. Based on this study, further investigations into effect of rough environments on ACF joints with different pitches will be of interest.