Electrodeposition of Refractory Metals from Some ZnCl2 Based Molten Salts at 150-250{degree sign}C

Abstract

The solubility of WO3 in a eutectic NaCl-KCl-ZnCl2 (20:20:60 mol%) melt at 250 {degree sign}C was increased by addition of KF, which enabled the electrodeposition of metallic tungsten. A smooth and dense tungsten film having 0.7 μm thickness was obtained on a nickel substrate by potentiostatic electrolysis at 0.06 V vs. Zn(II)/Zn for 3 h in the NaCl-KCl-ZnCl2-KF(4 mol% added)-WO3(0.54 mol% added) melt at 250 {degree sign}C. The surface of the nickel contact probe pin for semiconductor testing, which had been manufactured by the conventional LIGA process, was successfully coated with tungsten by using this molten salt. To lower the electrodeposition temperature, a new molten salt system, EMPyrCl-ZnCl2, was developed. An equimolar EMPyrCl-ZnCl2 system was a stable liquid at 40-200 {degree sign}C. A metallic molybdenum film was electrodeposited on a nickel substrate in the melt containing KF and MoCl5 at 150 {degree sign}C.