Solvent presence and its impact on the lap-shear strength of SDS-decorated graphene hybrid electrically conductive adhesives

Abstract

The mechanical bonding strength of electrically conductive adhesives (ECAs), as well as the impact of residual solvent on the bonding strength was investigated between a copper clad FR-4 surface and conductive adhesives using Lap-shear testing. Both solvent-free and solvent-assisted formulations with various filler concentrations of silver (Ag) and sodium dodecyl sulfate (SDS)-decorated graphene (Gr(s)) in epoxy matrices were prepared and compared. It was found that the introduction of 0.75wt% Gr(s) in solvent-free formulations increased the Lap-shear strength (LSS), while the combination of ethanol solvent and SDS in solvent-assisted formulations significantly decreased the LSS. In addition, it was found that increasing the Ag content generally lowers the LSS for both the solvent-free and solvent-assisted formulations. By examining the structure and interface of both formulations using optical microscopy, surface profilometry and SEM, we found that the solvent-assisted formulations exhibit more voids at the surface of the paste and more bubble formation throughout the material compared to the solvent-free formulations. Therefore, the significant drops of LSS in solvent-assisted Gr(s)-filled formulations may be attributed to the formation of bubbles at the micron range during the curing process.