Conductive Coating Formulations with Low Silver Content

Polymer based conductive adhesive and coating materials are widely used in electronic applications such as die attach adhesives, conductive inks, antistatic coating and electromagnetic interference (EMI) shielding. These materials are usually heavily filled with metal fillers, typically silver. To obtain electrical conductivity, a percolated filler network has to be formed in the material. The percolation threshold for most fillers is quite high. As a result, most polymer based conductive formulations have very high silver loading (70-85%wt). High silver loading results in high overall cost of the product and other issues, such as high viscosity and poor dispensability. In this article, we report a method to obtain electrically conductive coating with very low silver loading by combining metal particles with polymer latex particles. The latex particles are considerably larger than the metal particles and create excluded volume to decrease the percolation threshold of the metal particles. Silver percolation threshold of less than 3.6%vol has been demonstrated. When silver nanoparticles are used in the coating compositions, the electrical conductivity can be significantly improved after annealing at elevated temperatures, because of the low temperature sintering behavior of the silver nanoparticles. Electrical resistivity in the range of 10^-4Ω.cm has been achieved.