Metal Fume-Free Welding Technology for Advanced Semiconductor Grade Gas Delivery System

The most important part in the tubing construction of the ultraclean gas delivery system is the automatic butt welding technology. The welding process, in which metal needs to be turned into a molten state to be welded, always causes the generation of metal fumes. Manganese (Mn) is easier to evaporate and redeposit in the vicinity of the weld bead during the welding process because the vapor pressure of Mn is higher than that of other metal elements composed of stainless steel. It is revealed that the redeposited Mn is a trigger for the corrosion for a corrosive gas delivery system. The postwelding ultrapure water rinse has a good effect on removing the redeposited metals on the stainless steel surface. In an attempt to further suppress metal fumes generated during the welding process, the high-speed single-path narrow bead welding process is newly established. Its technique is characterized by a welding speed of 30 rpm, single path, and a bead width of 1 mm. Moreover, in order to reduce the generation of Mn fumes, the high quality material which reduces the Mn content in the base metal from the conventional 0.65% down to 0.01% is introduced and evaluated. As a result, the quantity of redeposited Mn on the downstream location of the weld bead is reduced to less than 1/3300 as a compared to that of the conventional welding technique (7.5 rpm x 2 paths, bead width 2 mm). Therefore, the corrosion resistance around the weld bead is greatly enhanced in comparison with the conventional welding method.