Effect of glass composition on sinterability of copper terminal paste for multilayer ceramic capacitors

Low-melting glass with an optimal composition should be developed for application to Cu electrodes in multilayered ceramic capacitors (MLCCs). This study evaluated the glass transition temperature, plating solution resistance, and wettability of glass melts on Cu substrates for low-melting glass with a conventional composition and compositions of BaO, TiO2, ZnO, and V2O5 added to 46SiO2/27B2O3/27Na2O (mol%). Moreover, we produced a Cu electrode paste for an MLCC using the designed glasses and evaluated the characteristics in terms of terminal electrode sintering. The plating solution resistance was improved by adding TiO2 to 46SiO2/27B2O3/22Na2O/5BaO (mol%) glass. Furthermore, adding V2O5 improved the glass melt fluidity while maintaining the plating solution resistance, thereby improving the Cu base wettability. Compared with conventional glass, the 45.0SiO2/17.6B2O3/16.6Na2O/4.9BaO/2.1V2O5/8.8TiO2/4.9ZnO (mol%) composition formed glasses with low transition temperatures, good Cu wettabilities, and superior plating solution resistances. The fired film of the Cu electrode paste using this new glass was inferior in sintering as compared with the conventional glass and did not become densified. As a result of measuring the amount of carbon in the fired film, it was found that the new glass has a larger amount of residual carbon than the conventional glass. In addition, a reaction layer with ceramic is confirmed in the new glass, and there is concern about ceramic embrittlement due to crystal precipitation and cracks. For practical use of new glass as an electrode paste material, removal of residual carbon and suppression of ceramic reaction are considered to be future issues.