Test rig for welding diamond wires into a loop

Abstract

The multi-wire sawing of silicon using a steel wire coated with diamond grits (diamond wire) is an important process in the semiconductor and photovoltaic industry. The cut is performed in the industry by pushing a silicon ingot against a diamond wire web that moves in a pilgrim-mode (forwards and backwards). As the cut direction and cutting speed of the wire change multiple times during the operation, it is very difficult to perform a proper investigation of the cutting process. In order to study the multi-wire sawing of monocrystalline silicon (mono-Si), a new experimental setup has been proposed. Based on literature research and industry know-how, the main features necessary for the proposed wafering test rig have been defined as follows: i) use of a short wire looped segment; ii) cut with controllable constant wire speed and iii) permit to track specific diamond grains after each cut for wear analysis. In order to fulfill these prerequisites, the first step is to butt-weld diamond wires into looped shape in a wire outer diameter range of 200 < OD < 500 μm. The adopted solution is a resistance butt-welding device. In this device, the wire ends are clamped with tight alignment. By the application of electric current through the wire ends interface, heat is generated by Joule effect and the incandescent heated material is pressed together with controlled force, creating the joint. After the joint is formed, a lower electric current heats the joint for a tempering procedure to increase material ductility. The conceptual design of the device is presented, followed by details of the actual device. Butt-welds of diamond wires with OD = 200 μm and 350 μm were successfully done, resulting in welded joints with good alignment, and sufficient tensile strength for the endless wire sawing application.

Effect of cutting parameters on surface integrity of monocrystalline silicon sawn with an endless diamond wire saw

“…Thus, instead of using a few thousand meters of wire for a multi-cut, single cuts were performed using only around a 1-meter segment of diamond wire. The ends of the industrial diamond wire segment were butt-welded on a welding device developed by Knoblauch et al (2017b). After the loop shape had been obtained, the diamond wire was wrapped around two Teflon® discs and moved by the driven rotary axis with constant rotation to perform the cut with a constant wire cutting speed (v c ).…”