Pan Pacific Symposium Conference Proceedings

Novel Nanofiber Anisotropic Conductive Films (ACFS) For Fine Pitch Assembly

Authors: Kyung-Wook Paik, Tae-Wan Kim, Sang-Hoon Lee, and Kyoung-Lim Suk
Company: KAIST Department of Materials Science and Engineering
Date Published: 2/11/2014   Conference: Pan Pacific Symposium

Abstract: Anisotropic Conductive Films (ACFs) have been widely used as excellent interconnection materials in semiconductor and display applications for chip-on-glass (COG), chip-on-flex (COF), chip-on-board (COB), flex-on-glass (FOG), flex-on-board (FOB), flex on flex (FOF) interconnections due to their fine-pitch capability, simple process, and cost effectiveness. However, less than 20 um COG and COF and less than 100 um FOF assemblies become challenging because of the electrical short between neighboring electrodes by agglomerated conductive particles in ACFs. Therefore, it is necessary to restrict the conductive particles movement during ACF bonding process, and solve the short problem at ultra-fine pitch.

For this purpose, novel nanofiber ACFs have been invented by Paik et al, and successfully solved the electrical short problems at the fine pitch COG, COF, and FOF applications. For nanofiber ACFs, about 200 ~ 500 nm diameter polymer nanofibers with coupled conductive particles are fabricated using an electro-spinning of polymer solutions mixed with conductive particles, and then nanofiber ACFs are successfully made by laminating NCFs (nonconductive films) on top and bottom side of the nanofibers with coupled conductive particles. This novel nanofiber ACFs show excellent electrical bump contact resistance, and electrical short free at ultra-fine pitch applications. Nanofiber ACFs can completely solve the electrical shortage problems at 7 µm bump-to-bump gap and 20 micron ultra-fine bump pitch of COG and COF and also less than 100 micron pitch FOF electronic packaging applications. It is because the movement of conductive particles during ACF assembly can be completely limited by the nanofiber anchoring effect resulting in about 3 times higher conductive particles capture rates compared with conventional ACFs.

Detailed information of nanofiber ACFs formation, COG and COF assembly processes, COG and FOF characterization using nanofiber and conventional ACFs will be presented.

Key Words: 

nanofiber, Anisotropic Conductive Films (ACFS),

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