Leitpastenentwicklung für Aluminiumnitrid-Keramik

Aluminum nitride ceramics (AlN) became of interest as substrate material for hybrid manufacturers. Its high thermal conductivity and the TCE close to that of silicon make it well suited for MCM's and high power circuits. Furthermore it is nontoxic compared to BeO. However the practical use of AlN is dependent on the availability of reliable metallization technics. Usual thick film pastes which were developed for alumina (Al2O3) often show incompatibility with AlN because of the interaction of the contained inorganic binder (often PbO-B2O3-SiO2 glasses) and the substrate during the firing process, resulting in an disturbed interface between the ceramic and the functional layer. This may lead to poor adhesion of conductor paste systems. The investigations made with glasses of the system BaO-SiO2-B2O3, which is thermodynamically stable towards AlN, showed the possibility to develop Ag/Pd-conductive pastes with good properties on AlN. Additives which vary the viscosity of the used glasses influence significant the initial adhesion, the adhesion durability after high temperature annealing and the solder wettability of the metallic layer. Crystalline phases caused by the additives seem to be responsible for the increase in adhesion strength. The developed Ag/Pd conductive paste has a sheet resistivity of 20-24 mOhm/sq and an inital adhesion of more than 28 N/4 qmm (wire peel test). After storage at increased temperature of 150 degree C for 1000 hours the adhesion remains constant at about 20 N/4 qmm.