MAGNESIA AND YTTRIA BASED COATINGS FOR DIRECT-COPPER-BONDING OF SILICON NITRIDE CERAMICS

摘要

Besides excellent bending strength, high fracture toughness and good thermal conductivity Si_3N_4 ceramics are of great interest for DCB substrates in power electronic applications. Unlike oxide ceramics like Al_2O_3, which are commonly used as a DCB substrate, it is hard to produce DCB coated Si_3N_4 circuit boards due to poor bonding of Cu. Therefore this work investigates adherence mechanisms between copper and MgO or Y_2O_3 coated Si_3N_4 ceramics, respectively. Oxide layers of various composition and thickness were formed by sol gel technique via dip coating. The microstructure was characterized by grazing incidence XRD and SEM as a function of Si3N_4 oxidation and annealing. The stability of the compounds and the reversibility of chemical reactions appear to be dependent on the amount of oxygen present in the system as well as on layer composition and structure. The bonding strength of the Cu metallization on the coated Si_3N_4 was determined by shear tests. The chemistry of the substrate strongly affects the interfacial bonding strength Copper on MgO coated Si_3N_4 exhibited higher peel adhesion strength than on Y_2O_3 coated Si_3N_4 This could be attributed to the formation of different reaction products in the interface and a pore-free contact area.