Ultra-thin chip-in-flex (CIF) technology using anisotropic conductive films (ACFs) for wearable electronics applications

For improving the flexibility and compact package size, chip-on-flex (COF)/chip-in-flex(CIF) assembly using Anisotropic Conductive Films (ACFs) as interconnection materials are investigated for flexible packaging technology of wearable electronics applications. The fatigue reliability of COF/CIF packages under dynamic bending environment was investigated. COF packages were successfully fabricated using ACFs with 40 um thin silicon chips and flexible substrates. By attaching the cover adhesive film with a polyimide film to COF packages, CIF packages were successfully fabricated as well. Through both convex and concave dynamic bending test, the thickness of cover adhesive film was optimized and then the minimum bending radius was obtained at no chip-crack condition. After fabrication of CIF packages with optimal cover adhesive film thickness of 30 um, and the effect of 3 types of ACFs on the dynamic bending performance of CIF packages up to 160 k cycles was also investigated. CIF packages using ACFs of higher modulus showed excellent fatigue reliability and stable ACF joints without delamination or resin crazing during dynamic bending test conditions.