Abstract: An inexpensive, very fine wire of high-purity copper is disclosed as an alternative to the fine gold wire which is currently used in the bonding of semiconductor devices. The very fine wire of high-purity copper is prepared from a copper ingot that contains 0-2 ppm of S, 0-2 ppm of Ag, 0-1 ppm of Se and 0-1 ppm of Te as incidental impurities with the total content of these and any other incidental impurities present being held at a level not exceeding 10 ppm. By subjecting it to an appropriate heat treatment, the wire acquires an elongation of 5-22%, a breaking strength of 14-33 kg/mm.sup.2, and a Vickers hardness of 38-50, the latter value being measured with respect to said high-purity copper in an ingot form.

Abstract: A soft solder of Pb alloy for semiconductor devices that contains 1 to 65 wt % of Sn or In or both, the balance being Pb and incidental impurities which include less than 50 ppb of radioisotopes and the count of radioactive alpha-particles being not more than 0.5 CPH/cm.sup.2. The solder exhibits high adhesive strength and good wettability. The properties of this material may be further improved by addition of 1 to 10 wt % of Ag.