Effect of Spiky Silver Filler Morphology on Conductive Path Formation and Electrical Resistivity in Epoxy-Based Electrically Conductive Adhesives

Electrically conductive adhesives (ECAs) present attractive alternatives to conventional solder materials, enabling low-temperature bonding and fluxless processes. This study investigated ECAs containing either spherical or spiky silver (Ag) fillers to clarify the effect of filler morphology on volume and interfacial electrical resistivity. The ECAs were prepared using thermosetting epoxy resin and cured on printed circuit boards. Volume electrical resistivity and interfacial resistivity were measured as a function of filler volume fraction. The percolation threshold was found to be approximately 13 vol.% for spherical fillers and 10 vol.% for spiky fillers, indicating the latter can form conductive networks more efficiently. Three-dimensional FIB–SEM observations revealed that each spiky particle possessed multiple protrusions establishing several contact points with neighboring particles and the Cu electrode. Numerical simulations using a particle dispersion model were also conducted to evaluate the number of continuous conductive paths. The simulation demonstrated that ECAs with spiky fillers possessed a greater number of conductive paths and electrode contact points than those with spherical fillers. These results demonstrate that spiky Ag fillers can effectively lower both volume and interfacial resistivity by forming multi-contact conductive networks in ECAs.