A Study on the Flexible Chip-on-Fabric Assemblies Using Anisotropic Conductive Films and Metal-Laminated Fabric Substrates

Abstract

In this article, chip-on-fabric (COFa) assemblies using anisotropic conductive films (ACFs) and metal-laminated fabric substrates were investigated. To fabricate the metal-laminated fabric substrates, electroless nickel-immersion gold (ENIG) metal-finished Cu circuits were fabricated on the B-stage nonconductive films (NCFs), followed by laminating onto the fabrics. Then, the 50- $\mu \text{m}$ -thick Si chip was bonded onto the fabric substrates using ACFs with a thermocompression (T/C) bonding method. First, the ACFs' joint properties, such as electrical resistances and adhesion strengths, were evaluated and compared with conventional chip-on-flex (COF) assembly. To enhance static bending flexibility without chip fracture, chip-in-fabric (CIFa) assemblies were developed after optimizing the thickness of a cover layer on the Si chip. Finally, mechanical and moisture-related reliability of the CIFa packages was evaluated through dynamic bending, 85 degrees C/85% relative humidity (RH), and washing reliability.