A new hybrid power technique utilizing a direct Copper to ceramic bond

A new technique of bonding copper directly to ceramic, employing the copper-copper oxide eutectic melt, is described. Scanning electron micrographs (SEM) and EDAX are used to study the details of this bond. A specific utilization of these techniques is portrayed in a 2-SCR-3-diode controlled bridge. This bridge is used as a 2-hp dc motor speed control. The advantages of using these techniques over previous methods (thick film or moly-manganese) lie in the ability to bond almost any thickness of high-conductivity copper to ceramics (Al2O3, BeO, BN, ZnO, etc.) silica, dissimilar metals, or to copper itself. Incidental benefits, described in the report, include bonding copper lead frames instead of screen printing, lack of high thermal and electrical resistivity interface layers, and simplicity of manufacture. Ceramic properties found to influence bond quality were: 1) Topology in terms of a fractured surface due to lapping and/or die sticking. 2) Degree of intergranular bond strength. 3) Cleanliness of surface and degree of unbonded particulate matter (powder) on the surface. 4) Grain size. The bonding agent is characterized as a field of bonded Cu2O nodules precipitated from the Cu-Cu2O eutectic melt with a density much higher than expected from the 4.7-percent Cu2O (by volume) contained in the eutectic mixture. Mechanisms to explain this behavior are described. The bond strength is noted to depend on the nodule density and the bond strength of the Cu2O to copper and is higher than any other bonding method.