Preparation And Properties Of Copper Conductive Paste For Low Temperature Co-fired Ceramics

Inthispaper,SiO₂-B₂O₃-ZnO,SiO₂-B₂O₃-CaO,SiO₂-B₂O₃-BaO,SiO₂-B₂O₃-ZnO-CaO,SiO₂-B₂O₃-ZnO-BaO and SiO₂-B₂O₃-ZnO-MgO glass powders were prepared by sol-gel method.The glass powders with different melting characteristic were chosen and mechanically mixed with Cu powder and organic vehicle to prepare copper pastes.Then the pastes were printed on LTCC substrate and co-fired with the substrate.Besides,glass gel coated Cu powders with different glass ratio were prepared through sol-gel process and then heat treated in N₂ atmosphere at600?C or 800?C to improve their oxidization resistance.The copper pastes were prepared by mixing the glass gel coated Cu powders and organic vehicle.Air and N₂were used in binder-burning out process respectively followed by sintering in N₂ to obtain conductive copper films.The microstructures and properties of glass powders,glass gel coated Cu powders and copper films were analyzed by SEM,TEM,XRD,etc.Amorphous phase glass powders with small particle size and good uniformity were obtained by adding dispersants and ball-milling in the preparation of the glass by sol-gel method.The melting and wetting behavior of the glass powders on LTCC substrate were studied.The glass with the composition of SiO₂:B₂O₃:BaO=10:55:35（wt.）melted and wetted the substrate well at 900oC.And the copper film with the glass showed the smallest sheet resistance after being sintered in N₂ at 910oC.The optimum coating layer of the glass gel coated Cu powder was obtained at coating temperature of 70?C and coating time of 3 h.When the glass amount was small,the surface of the glass gel coated Cu powder was smooth.With the increase of the glass,the coating became more compact,and the surface became rougher.The coating layer with 1 wt.%¹1 wt.%glass all inhibited the oxidation of Cu powders,and the oxidation resistance increased with the increase of glass amount.The cracks,holes and other defects in the coating layer reduced when the glass gel coated Cu powders were heat treated in N₂,which further improved the oxidation resistance of the glass gel coated Cu powders.Compared with the film prepared by mechanically mixing,the sintered copper film prepared with glass gel coated powders had better electrical conductivity.Due to the improvement of the oxidation resistance of the glass gel coated Cu powders,the copper films could be binder-burned out in air at 400?C with slight oxidization,and the copper films combined with the substrate well after being sintered in N₂ at 910?C.The sintered film with 9 wt%glass coating showed the smallest sheet resistance of 1.3mΩ/□,which can be used as good conductive thick film on LTCC substrate for microelectronic packaging.