Effects of metal surface finish on the anisotropic conductive adhesives (ACAs) joints

This work was performed to investigate the effect of final surface finish of Cu electrodes on the adhesion and reliability of anisotropic conductive films (ACFs) joints. Two different materials, electroless Ni/immersion Au (ENIG) and organic solderability preservatives (OSPs), were selected because these materials has been most commonly used as the final surface finish materials in printed circuit board (PCB) industries. However, the effect of OSPs on the adhesion and reliability of ACF joints has not been studied. Therefore, 1) investigation of the adhesion of ACF/OSP joints, and 2) evaluation of the reliability of ACF/OSP joints were performed in this study. Then, the results of ACA/OSP joints were compared to those of ACF/ENIG to confirm the feasibility and reliability of ACF/OSP joints. Adhesion strengths of ACF/OSP joints were also higher than ACF/bare Cu and ACF/ENIG joints. The fractured site of ACF/bare Cu and ACF/ENIG joints was ACF/metal interface but that of ACF/OSP joints was ACF inside. TEM and FT-IR analyses showed that the OSP coating layer on Cu electrode remained even after ACF bonding and it seemed to play as an adhesion promoter