satisfactory strength requirements may be obtained with about 2 to less than 4 weight percent for the submicron refractory metal particles and 10 to less than 30 weight percent for the larger refractory metal particles as is apparent the effects of grain size control and shrinkage control may advantageously overlap at the small amounts of refractory metal additive contemplated by the present invention in use the copper based paste according to the present invention is screened onto a ceramic greensheet to form vias and or lines and then sintered referring now to fig2 there is shown a multilayer ceramic substrate 10 having co fired vias 20 and lines 22 the greensheet may comprise a variety of materials including but not limited to mullite borosilicate glass cordierite glass other ceramic materials etc the cordierite glass ceramic materials such as that disclosed in kumar et al u s pat no 4 301 324 the disclosure of which is incorporated by reference herein are preferred preferably the copper powder has an average particle size of about 5 to 8 microns the resultant vias and lines have a composition that is mostly copper with smaller amounts of the refractory metal additive the precise composition will track closely to that of the solids content of the paste for smaller amounts of the refractory metal additive the bulk ceramic material may be allowed to densify to 90 or more of theoretical density for larger amounts.