Interaction of Ag/Pd Metallization with Lead and Bismuth Oxide-Based Fluxes in Multilayer Ceramic Capacitors

An ongoing challenge for future developments in high-performance ceramic multilayer capacitors and integrated ceramics is to reduce the internal electrode cost and thickness without sacrificing yield or reliability. Key to these developments is a thorough understanding of the interactions which occur between flux-sintered dielectrics and low-cost, Ag/Pd electrodes. In this paper we present results on the pahse equilibria of Ag/Pd electrode systems with Bi₂O₃ and PbO fluxes. The conditions under which the bismuth reaction occurs and reactions in the Pd–PbO system are reported. Results show that the equilibrium phases which form depend strongly upon the Ag/Pd ratio and temperature. These phases include PdBi₂O₄, Pd(Bi), PdPbO₂, Pd(Pb), and PbPd₃. The PdBi₂O₄ and PdPbO₂ phases decompose when PdO destabilizes, resulting in a series of reactions which result in oxygen evolution and partial melting of components. The exact phase relations of the Ag/Pd–Bi₂O₃–O₂(air) system and Ag/Pd–PbO–O₂(air) system have been established for the first time and are discussed in terms of their impact on multilayer, cofired structures.