Applying SU-8™ to the fabrication of micro electro discharge machining electrodes

Abstract

Taking advantage of high aspect ratio micro structure technology (HARMST) allows a cost competitive approach to batch fabricate a high number of tool electrodes for micro electro discharge machining (EDM). A new type of EDM tool micro electrode fabrication was developed using a combination of near UV lithography to directly polymerize a micromold made of SU-8 TM in combination with electroplating. Applying SU-8 TM for the fabrication of deep hollow micromolds, an ultra-thin resist film remains on the seed layer at the bottom of the micromolds. This remaining undeveloped resist film at the bottom of the mold prevents the electro deposition on the conductive seed layer. The PVA Tepla PS4008 plasma ashing system was investigated to remove the resist residually from the SU-8 TM micromolds before electroplating without destroying the micromold itself and to remove the entire micromold after the fabrication of the micro electrodes selectively.

High aspect ratio micromolds for the electroplating of micro electro discharge machining tools

“…4. Traisigkhachol et al (2010) found such SU-8 TM residue on the Au seed layer at the bottom of the SU-8 TM micromold and removed it with plasma ashing. For the electroplating of high micro electrodes, the seed layer has to feature a high adhesion to the electrode.…”

“…Au was deposited using magnetron sputtering. Unfortunately, Cu provided only a poor adhesion to the SU-8 TM micromolds (Traisigkhachol et al 2010). By applying Ni as an interlayer between the Cu seed layer and the SU-8 TM micromolds, a better adhesion and chemical resistance was achieved.…”

“…4a, the SU-8 TM residue was found at the bottom of the micromold, followed Traisigkhachol et al (2010). Using a Cu seed layer such an SU-8 TM residue was not found, but the SU-8 TM micromold needed an adhesion layer as shown in Fig.…”

“…The material removal during a Micro-EDM process is caused by applying a pulsed electrical voltage between the two electrodes and can be broken down in four phases as shown in Fig. 1 adapted from Piltz (2007). The first phase starts with the application of the pulsed high voltage; during it, the dielectric fluid is ionized, (Fig.…”

“…Electrical and thermal conductive materials with high melting points and low thermal expansion are normally used for EDM tool electrodes (Piltz 2007;Kanani and AliAbassi 2000;Heeren et al 1997). Those kinds of materials are extremely difficult to fabricate, in particular on micro scale.…”