Studies on Brazability of Electric Contact Chip Materials (Report 1)

Effect of Surface Preparation on Wetting of BAg Filler Metals on Tungsten Base Sintered Alloys

Abstract

Surface preparation of tungsten base sintered alloys (Ag-W, Cu-W alloy) was studied to improve the wetting of BAg filler metals. Several interesting results were obtained as follows.
(1) The etching treatment of Ag-W or Cu-W sintered alloy in molten NaNO₂ made the surface rich with silver or copper by selective dissolution of tungsten. The improvement of spreadability of BAg filler metals on Ag-W or Cu-W sintered alloy was gained by means of the etching treatment in molten NaNO₂.
(2) The addition of nickel metal to silver filler metal or to sintered alloys improved the spreadability a little with similar effect to the etcing treatment.
(3) By the addition of CoCL₂ or NiCL₂ to the fluoride system flux, the spreadability was greatly improved, due to the deposition of Co or Ni from CoCL₂ or NiCL₂ on the surface of sintered alloy.