Arun Arora
KIST Europe, Korea Institute of Science and Technology, Campus E7.1, 66123 Saarbrücken, Germany
Background
An electrochemical spark erosion method is presented to drill holes in glass substrates or thermally bonded glass chips. Shohi and co-workers [1] reported this method in 1990. We have modified the method by using a Pt wire 0.5 mm diameter anode instead of a steel needle cathode as a drilling needle and 50 V (instead of 35 V) was applied from a variable unregulated dc power supply to produce a constant spark in 8 M sodium hydroxide solution. When a steel needle cathode was used as reported in reference Shohi’s method, a large amount of brown precipitate was formed, which entered into the channel and created blocks.
Figure 1 shows a schematic diagram of the complete process and Figure 2 is a photo of the setup showing the process in operation.
- Figure 1: Electro chemical spark erosion method of drilling holes in a thermally bonded glass device
- Figure 2: Photo of the electro chemical spark erosion method for drilling holes in a thermally bonded glass device
The conventional methods to drill holes in glass include laser ablation or powder blasting. Both methods require expensive setup and trained staff therefore these methods are expensive. The dentist drill also used to drill holes in bonded glass devices which can cause stress to the glass or can damage the channel walls. Sometimes glass particles can also clog the channel. A simple method for drilling access hole in a glass substrate or a thermally bonded glass chip is presented.
What do I need?
- Pt wire (0.5 mm diameter)
- Sodium Hydroxide solution (8M) (Caution)
- Variable DC Power supply (100 V)
- Petri dish
What do I do?
- Fixed a pt wire cathode on the side of the Petri dish as shown in schematic diagram in figure 1 or the photo in figure 2. Make sure that Pt wire reaches to the bottom of the petridish so it can make contact to the sodium hydroxide solution.
- Wear gloves and safety goggles and then place the Petri dish on a dry table. Fill it with sodium hydroxide (8M) solution (Caution: sodium hydroxide solution can cause severe burn if it comes in contact with skin. If any part of the body comes in contact, immediately wash it off with plenty of water.)
- Mark the position for the hole using a glass marker pencil on other side of the glass substrate where you want to drill the hole. Place it in the Petri dish facing the mark downward and immersed it approximately 5 mm deep into the sodium hydroxide solution.
- Connect the PVC covered anode and Pt wire cathode to the DC power supply.
- Hold the PVC covered Pt electrode precisely over the marked position on the glass substrate. Switch the power supply on and increase the voltage until the orange spark become visible. After 5 to 10 seconds of constant spark check the progress of drilling by taking out the glass substrate and viewing it with a hand held magnifying lens or a microscope (Figure 3).
- Figure 3: Photo of the hole drilled by electrochemical spark erosion; a) Hole across a 60 µm wide channel. b) a 500 µm diameter hole across a 60 µm wide channel in a pre-bonded capillary electrophoresis glass device
References
[1] Shohi, S.; Esashi, M. Photoetching and Electrochemical Discharge Drilling of Pyrex Glass, Technical Digest of the 9th Sensor Symposium, Japan, 1990, 27.
