Electrical property improvement of dicyandiamide-cured electrically conductive adhesives through in-situ replacement by difunctional acids and the impact on storage

To improve the electrical conductivity of the dicyandiamide-cured electrically conductive adhesives (ECAs), short-chain difunctional acids with various structures including oxalic acid, succinic acid, adipic acid, phthalic acid and cis-hexahydrophthalic acid were introduced in-situ to replace the commonly used surfactant-stearic acid on the silver filler surface. Oxalic acid, phthalic acid and cis-hexahydrophthalic acid deteriorated the electrical conductivity of ECAs whereas the electrical conductivity was improved significantly with the addition of succinic acid and adipic acid. Moreover, the storage performance, viscosity, curing behavior, bulk resistivity and the shear strength of ECAs with varied content of adipic acid had been further studied. With the increment of adipic acid, the curing temperature of ECAs decreased, while the reaction between dicyandiamide and adipic acid happened as the content reached 0.3 wt%. And the adipic acid not just improved the electrical conductive, but also improved the shear strength without adversely affected the storage performance of ECAs. As the content of adipic acid reached 0.3 wt%, the lowest bulk resistivity 3.8×10−4 Ω cm was obtained, at the content of 0.5 wt%, the shear strength was improved to 18.5 MPa.