Enhancing µ-WEDM and EDM (wire/electro-discharge) of doped silicon

Abstract

Electro-Discharge Machining and Wire Electro-Discharge Machining are nonconventional machining technology which is extensively used for metal based fabrication process. This process enables machining of any material, which is electrically conductive, irrespective of its brittleness, hardness or strength, therefore conductive material is usually easy to machine by µ-WEDM and µ-EDM. Si which is the workpiece in this research is a semiconductor material with high resistivity and it is difficult to machine by µ-WEDM and µ-EDM. Thus, the machining of Si can be enhanced if it is possible to increase the conductivity of this semiconductor. This study aims develop and characterize the process of enhanced µ-WEDMing and and µ-EDMing of Si by temporary coating this Si with a high conductive metal (gold in this study). The methodology of this work started with the coating the Si workpiece with gold (Au) using sputter machine. Then µ-WEDMing and µ-EDMing processes were carried out. The workpiece samples prepared for characterization through cleaning these samples by ultrasonic machine. The characterization was carried out using the Scanning Electron Microscope (SEM) machine. WEDM process stability was found to be improved (up to 60 times for certain machining condition) if coated Si wafer is used as compared to uncoated Si workpiece. Material removal rate was also found to be increased by a good margin (~ 30% average) for coated Si wafer. Machined slots were found to be more uniform though kerf width was slightly larger for coated Si wafer. In the case of EDM, the process stability for coated Si was found to be more stable than uncoated Si especially for high discharge energy. MRR for gold coated silicon samples was higher than uncoated silicon sample (about more than 10 x for 85V and 10 nF machining condition). Overall this new method of µ-WEDM and µ-EDMing operations of polished Si wafer has been found to be more efficient and useful. Removal of the conductive coating without damaging the substrate is a challenge for this process which was carried out successfully by selective etching method. ?