Microstructure, resistivity, and shear strength of electrically conductive adhesives made of silver-coated copper powder

Electrically conductive adhesives were made using silver-coated copper powders (filler) and epoxy. Resistivity, microstructure and shear strength of prepared adhesives were studied using two-point resistance measurements, Scanning Electron Microscope (SEM) and universal tensile tests, respectively. Effect of filler concentration (70-85 wt%), silver concentration (10-50 wt%), particles morphology (flake or spherical) and addition of graphite (2-15 wt%) were investigated on prepared adhesives properties. Results showed that by increasing the filler percentage from 70 to 85 wt%, the electrical resistivity decreases from 6.2 x 10(-3) to 3 x 10(-3) Omega.cm. Furthermore, the electrical resistivity of adhesives is proportional to the silver content of the filler particles. Regarding the morphological effect of filler particles, it was found that by replacing 40 wt% of the flake with spherical particles in the adhesive with a filler content of 75 wt%, the electrical resistivity of the adhesive reduces from 5.6 x 10(-3) to 4.5 x 10(-3) Omega.cm, while the electrical resistivity of the adhesive containing 50 wt% of the spherical particles reached to 1.1 x 10(-2) Omega.cm. Graphite addition to adhesive formula in concentrations less than 6 wt%, slightly lowered the resistivity of the adhesives. Increasing the graphite addition from 6 to 15 wt% enhanced the electrical resistivity from 2.8 x 10(-3) to 1.7 x 10(-2) Omega.cm. The shear strength of the adhesives is inversely proportional to the filler percentage in the adhesives.