Authored By:
Seung-Yoon Jung, and Kyung-Wook Paik
Nano Packaging and Interconnect Lab. (NPIL)
Department of Materials Science and Engineering
Korea Advanced Institute of Science and Technology (KAIST)
Daejeon, South Korea
Summary
In this study, flexible Chip-In-Fabric (CIF) assemblies using anisotropic conductive films (ACFs) and cover layer structure were demonstrated. Fabric substrates were fabricated by Cu pattern lamination method with additional Electroless Nickel Immersion Gold (ENIG) metal finish before laminating onto the fabrics. Thermo-compression (T/C) bonding method was used to bond the 50µm-thick Si chip on the fabric substrates using ACFs. After T/C bonding, stable ACFs joint interconnection was formed between chips and substrates.
After polymer cover layer structure was applied, the minimum bending radius before chip crack drastically decreased down to 10 mm radius. In addition, a dynamic bending test was performed to evaluate the dynamic bending reliability of the CIF assemblies, and cross-section SEM analysis and digital image correlation (DIC) method were used to analyze the bending test results.
Conclusions
In this study, a novel Chip-In-Fabric assembly was demonstrated using Cu pattern-laminated fabric substrates and ACFs materials. After T/C bonding, ACFs joint was well formed between chip and fabric substrates. During the fabric substrates fabrication, the resin of the B-stage adhesive films permeated into the fabrics, and some part of the fabric substrates had porous structure. Therefore, the amount of ACFs resin permeated into the fabric substrates determined the final ACFs gap height and resulting electrical resistances.
Flexible COF packages were achieved by applying the polymer cover layer structure on top of flip-chip surface. After 195 um-thick cover layer structure was applied, encapsulated-CIF packages A and B showed the minimum bending radius of 7.4 mm and 9.5 mm respectively. In addition, encapsulated-COF packages A showed stable joint resistance after 100,000 cycles of dynamic bending at 12 mm bending radius for both convex and concave bending conditions.
As a result, highly flexible Chip-In-Fabric assemblies were achieved using ACFs materials, fabric substrates A, and 195µm cover layer structure. This encapsulated-CIF packages can be a promising solution for fabric-based wearable devices.
Initially Published in the SMTA Proceedings
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