Electrochemical migration behavior of silver nanopaste screen-printed for flexible and printable electronics

Electrochemical migration (ECM) - a potential problem in confined multi-layered circuits with narrow connections - was investigated with respect to the heat treatment of silver (Ag) nanopaste screen-printed on polyimide (PI) substrates. The Ag nanopaste patterns were sintered for 30 min at various temperatures. When the sintering temperature was raised from 150 to 300 °C the Ag cluster size increased with volumetric shrinkage and the electrical resistivity decreased. ECM was evaluated by thermal humidity bias (THB) testing and water drop (WD) testing, which both showed that the Ag nanopaste sintered at higher temperatures was required longer time to bridge the adjacent Ag electrode by the ECM phenomenon. Sintering at low temperatures led to the patterned surfaces showing larger surface areas, thereby expediting the increase of electrical resistivity and hastening short circuit during THB testing. Water drop testing revealed that ECM, and associated short-circuit failure by dendrite formation between the cathode and anode, decreased with increasing sintering temperature. The dendrites were analyzed by field emission scanning electron microscope and electron probe micro analysis. The metallic dendrites, consisting of Ag oxidation products, formed as a mixture of trunk- and lace-type structures: Ag combined with H2O or OH anions to form oxides.