A study on Flex-on-Fabric (FOF) Interconnection Using Anisotropic Conductive Films (ACFs) and Ultrasonic Bonding Method

Abstract

Flex-on-fabric (FOF) interconnections using anisotropic conductive films (ACFs) and ultrasonic bonding method were investigated for wearable devices applications. In this paper, the conduction mechanism of FOF and the effects of the conductive fabrics porosity and ACFs materials on the FOF interconnection were investigated. Two types of conductive fabrics with different porosities such as knitted and woven fabrics, and different viscosities of ACFs resin were used. For the conductive particle of ACFs, metal-coated polymer ball was used. According to the results, the conduction of FOF consists of both conductive balls and fabrics to metal electrode direct contacts. Among these two conduction paths, fabric direct contact was the major conduction path because the contact resistance of the ACFs conductive balls to metal contact is about ten times larger than that of the fabric to metal direct contact. In addition, it was found that laminated nonconductive films cover layer and the increased ACFs minimum viscosity (from 940 to 27000 Pa.s) substantially increased the peel adhesion strength twice due to the decreased resin flow through the pore of fabrics and increased FOF joint gap size. Finally, both conductive fabrics showed no electrical failure after 500 h 85 degrees/85% relative humidity reliability test. However, among two types of fabric, knitted fabric had better humidity reliability performance than the woven fabric presumably due to its better compliance.