This paper describes the effect of solvent evaporation and shrink in conductive adhesive. The adhesion mechanism of conductive adhesive strongly depends on the curing of the polymer matrix. The curing is preceded by polymer matrix chemical reactions, such as cross-linking, solvent evaporation and shrink. Accordingly, it is important to understand the effect of solvent evaporation and conductive adhesive shrink in curing. The curing behaviors and solvent evaporation of conductive adhesive were investigated using a differential scanning calorimeter (DSC) and thermo gravimetric analysis (TGA). As curing time increases, the silver particles in the polymer are concentrated due to the incremental solvent evaporation rate and the shrink rate. As a result, the silver particles in the polymer form an electric path. These results reveal that the shrink rate and solvent evaporation rate increase in conductive adhesive during the curing process improved their conductivity.
Conventional conductive adhesives are composed of micro-sized filler metal and polymer matrix. Currently, the conductivity of conventional conductive adhesives is generated by small contact points formed among the particles during the curing process and by the tunneling effect. Therefore, conventional conductive adhesives generally exhibit higher electrical resistance than metal solder materials. In this study, a new class of conductive adhesive, composed of nano-particles and micro-particles in epoxy, was developed to improve electrical conductivity. This study used four conventional conductive adhesives (CCA1 to 4) and three hybrid conductive adhesives (HCA1 to 3). Scanning electron microscopy (SEM) observation was used to investigate the configuration of nano-particles and micro-particles. The electrical resistance of HCA1 to 3 was investigated and compared to CCA1 to 4 using a four-point probe method. When 2 mass% of nano-particle content was added to the micro-particle (HCA1), the electrical resistance decreased compared to CCA3. At 4 mass% of nano-particle content (HCA2), the electrical resistance value was similar to CCA3. However, at 8 mass% of nano-particle content (HCA3), the electrical resistance continued to increase, and exceeded that of CCA3.
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