Effects of organic binder on rheological behaviors and screen-printing performance of silver pastes for LTCC applications

Ethyl celluloses (ECs) organic binder with different molecular weights and contents was applied to silver pastes for LTCC applications. The effective spheres (S) of EC molecules are proportional to the molecular weight of ECs. Large EC molecular weight and content make the entanglement of polymer chains more significant and improve the strength of network structures inside organic vehicles and pastes, leading to the increase of viscosity and pseudoplasticity, which are beneficial to the screen printing of fine patterns for internal and external electrodes. However, high viscosity and short structure recovery time are not conducive to the screen printing of large area electrodes, resulting in enhanced surface roughness, such as R_a increased from 0.652 for STD 4-based silver paste to 1.803 for STD 300-based silver paste. Furthermore, the printing via-filling performance of silver paste with higher EC content and molecular weight is better, which possesses high viscosity, high pseudoplasticity, suitable thixotropy, and relatively slow wall slip rate. The fabrication of LTCC substrates with internal, external, and via electrodes confirmed the good performance of the home-made silver pastes for LTCC applications.