The copper surface must be smooth and free of scratches (if needed the surface may be re-polished using a suspension of fine alumina powder in distilled water). The iron-nickel alloy wire with the closest glass expansion coefficient is used as the core material, and the outer layer is covered with a good heat conduction and electrical conductivity copper layer.The surface is reworked to form a copper oxide film/barrel, which increases the composite line between the surface of the copper layer and the good sealing of the glass.