A Study on the Nanofiber-Sheet Anisotropic Conductive Films (NS-ACFs) for Ultra-Fine-Pitch Interconnection Applications
Nanofiber-sheet anisotropic conductive films (NS-ACFs) were invented to overcome the limitations of high joint resistance and short-circuit issues of ultra-fine-pitch interconnections. The NS-ACFs have great advantages in terms of suppressing conductive particle movement during the flip-chip bonding process. In a 20-μm ultra-fine-pitch with 7-μm bump spacing ultra-fine-pitch chip-on-glass assembly, suppression effects of conductive particle movement were significantly improved by using the NS-ACFs because an unmelted NS inside the ACFs suppressed the mobility of conductive particles so that they would not flow out during the bonding process. The NS-ACFs could significantly increase the capture rate of conductive particles from 31% up to 81% compared to conventional ACFs. Moreover, excellent electrical contact properties were obtained without melting the nanofiber material which was essential for the conventional nanofiber ACFs. The NS-ACFs are promising interconnection materials for ultra-fine-pitch packaging applications.