Copper Conductivity at Millimeter-Wave Frequencies

Copper was electrodeposited on steel substrates and annealed at 300° C in a nitrogen-filled oven. The conductivities of the deposits, measured at 43 GHz, were between 82 and 93 percent of the IACS (International Annealed Copper Standard) value of 5.8 × 107S/m. The conductivity of the plating is sensitive to minute changes in the concentration of copper cyanide and sodium cyanide in the plating solution. In all cases, the annealing step at 300° C effected a significant improvement in the copper conductivity. Special instrumentation was developed to permit accurate determination of the copper conductivity at millimeter-wave frequencies. An intrinsic accuracy of approximately 1 percent was achieved for the electrical measurement. When the variations due to the mechanical fixturing were included, the measured standard deviation for copper conductivities between 4.3 and 5.4 was typically 0.047 (x101S/m).