A Binder-Free Ag Paste Using a Chemically Adsorbed Monolayer

Abstract

We developed a binder-free Ag paste using reactive chemically absorbed monolayers (CAMs), such as epoxy-terminated CAMs. Ag paste was prepared by forming an epoxy-terminated CAM with 2-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane (ECHxES) on the surface of Ag particles, followed by adding 2-methyl-imidazole (2-MeIm) as a cross-linker into a suspension of dispersed Ag particles modified with ECHxES. To increase electrical conductivity, a mixture of large (average diameter D = 1.0 µm) and small (D = 0.5 µm) Ag particles was used. When the ratio in the mixture of large: small was 7:3, the best conductivity, 4.0 ×104 S/cm, was obtained. To prepare rigid wires from Ag paste, a cross-linker of a copper imidazole complex, instead of 2-MeIm, was added to the mixture of the Ag particles covered with ECHxES CAMs. The best pencil hardness and the best electrical conductivity obtained with the Ag paste wire were F and 2.5 ×105 S/cm, respectively, which exceeded the values of commercially available Ag pastes.