A Study on the Anchoring Polymer Layer(APL) Solder Anisotropic Conductive Films (ACFs) for Ultra Fine Pitch Flex-on-Flex (FOF) Assembly Using an Ultrasonic Bonding Method

In this study, APL solder ACFs combined with an ultrasonic bonding process are newly introduced. The effects of APL ACFs properties on conductive particle movement and interconnection stability of ultra-fine pitch COG applications were reported earlier. It was found that the APL structure will not only suppress the conductive particles movement during ACFs bonding process for ultra-fine pitch applications, but also prevent electrical short circuit formation between neighboring bumps. However, to achieve a stable electrical interconnection, the APL ACFs require additional process steps such as an oxygen plasma etch process to remove the APL polymer skins surrounding the conductive particles using a thermo-compression bonding method. However, during the vertical ultrasonic bonding process, it was found that the APL polymer skins of the conductive particles were successfully removed by a vertical ultrasonic vibration. Therefore, stable solder joint formation can be achieved without any additional plasma etching process needed for non-solder conductive particles.