PURPOSE: To maintain the matching capacity of thermal expansion coefficients between a ceramic board and a conductor and inhibit their conduction resistance to a minimum value by allowing conductor raw material powder to contain Mo at least and specifying their grain sizes and amount of added powder.

CONSTITUTION: Ceramic raw material powder and conductive raw material powder are laid out in a through hole of a ceramic board and fired and formed into a conductor therein. The conductive raw material is specified to contain at least Mo, and their minimum grain sizes are defined not to exceed 1.5μm while their amount of added powder is arranged to exceed 15wt.%. The ceramic raw material powder comprises Al2O3 powder while the conductive raw material comprises Mo powder and W powder (which may not be included.). The weight composition percentage of each raw material powder for the three components of Mo and W and Al2O3 is composed of Al2O3 powder (0.05 to 0.3) and Mo powder (0.3 to 0.95). However, the composition excludes the aforesaid Al2O3 powder, which ranges from 0.23 to 0.3 and the Mo powder which ranges from 0.3 to 0.55. Their resistance value is defined to be 4.0×10-5Ω.cm or below while their thermal expansion coefficient is defined to exceed 6.25×10-6/°C.