An electroconductive hole plug paste comprising about 60-80 wt % of platinum particles, about 10-20 wt % of Al2O3, and about 10-20 wt % of organic vehicle, based upon 100% total weight of the paste, wherein the organic vehicle includes at least one viscosity-modifying component in an amount sufficient to provide the electroconductive hole plug paste with a viscosity of about 800-1,500 kcPs, is provided. A ceramic substrate assembly for an implantable medical device having the electroconductive hole plug paste of the invention, and a method of forming the same, are also provided.