(A) study on the fabrication and flexible anisotropic conductive films (ACFs) interconnection of fine-pitch Cu pattern-laminated fabric substrates

Abstract

Recently, smart clothes based on the electronic textiles (e-textiles) technology have become one of the most promising form of the wearable devices over accessory-type devices such as glasses, watches and shoes. One of the approaches to realize e-textile system is to integrate conventional electronic devices onto the fabric substrates. To do that, interconnection of those devices onto the fabric is necessary and at the same time, fabric substrates should have electrical circuits to transmit electrical signals. In this thesis, a novel Cu pattern-laminated fabric substrate using B-stage adhesive films will be introduced. Cu pattern was directly formed on the adhesive films using conventional patterning processes, followed by lamination onto the fabric substrates. This method can provide fine-pitch and flexible fabric substrates, however to do that, investigation of the effects of the materials properties of the B-stage adhesive films are necessary.

As an interconnection method, anisotropic conductive films (ACFs) will be used in the thesis. ACFs are film- type adhesive materials consisting of thermosetting polymer resin and conductive particles. After simple bonding process, mechanical adhesion and electrical interconnection can be simultaneously formed by the resin and conductive particles each other. In addition, ACFs interconnection can be one of the solutions for flexible packaging. Therefore, ACFs interconnection of the fabric substrates using polyimide-based flex substrates and Si chip was demonstrated.

In chapter 2, the effects of the materials properties of the B-stage adhesive films on the lamination properties of the fabric substrates such as morphology and bending fatigue property were investigated. Curing property of the adhesive films was firstly optimized since the patterning process directly on the film caused resin pre-curing before lamination. In addition, the effects of film viscosity on the morphology of the fabric substrates were studied in terms of pattern integrity and cross-section morphology after lamination. Finally, the adhesive film modulus and adhesion effects on the bending fatigue properties will be investigated. Through this chapter, the adhesive films will be optimized in terms of pattern integrity and bending reliability.

In chapter 3, Flex-on-Fabric (FOF) interconnection using ACFs and a vertical ultrasonic (U/S) bonding method was demonstrated. For ACFs interconnection, electroless nickel immersion gold (ENIG) metal finish was performed on the Cu electrodes on the adhesive film before lamination. In this chapter, comparative study of the ACFs joint properties was done between fabric substrates and polyimide-based flex substrates. Joint morphology, contact resistance, peel adhesion strength, and pressure cooker test (PCT) reliability were evaluated.

Finally, in chapter 4, Chip-on-Fabric (COF) interconnection using ACFs was demonstrated. Thermo- compression (T/C) bonding method was used for ACFs bonding, and cover layer structure was applied on top of the flip-chip surface to protect Si chip under bending environment. The effects of cover layer thickness on the static bending property were investigated. And the reliability of the encapsulated COF packages was evaluated under dynamic bending, 85oC/85% relative humidity (RH), and washing environment.