Analysis of Electrical Forces in Multi-wire EDM for Semiconductors

Abstract Multi-Wire EDM (MWEDM) is being investigated for cutting silicon wafers from ingots in solar industry and IC manufacturing industry. However, practical realization of MWEDM is limited by the forces exerted on the wires. This paper explains nature of forces in case of MWEDM for slicing of silicon ingots, which is distinct from the case of single wire EDM for metal cutting. In particular, the material properties of semiconductor are different from those of the metals and the geometry of the problem is also different. It is shown that the wires in MWEDM exert forces on each other, in addition to those exerted by the workpiece on wires. Quantification of dominant electromagnetic forces is done by analytical means and the results are validated by Finite Element Analysis (FEA) for the cases of 5-wire EDM and 10-wire EDM. Experimentally determined material properties and spark current profiles are used as input to FEA. An algorithm has been developed to calculate the required wire tension considering number of wires, radius of wires, spark current, and wafer thickness. Validation of the algorithm is provided by comparing the results with the experimental data for 40-wire EDM published earlier.