RSSI had two circuit boards nagging me to be etched this morning. Without a photo developing tray, it seemed some modifications in technique were in order. Into the recycling bin I went, looking for a smallish, wide-mouthed glass jar. Yesterday's sandwich polished off a tasty mango chutney, and the jar was just about right. A little bit of cleaning, and it was ready for business.
The leftover etchant from yesterday's vinyl PCB resist adventure was in a plastic bottle and still had some potency. The tea water was hot on the stove, so it was ready to provide some double-boiler action. I poured some hot water into a steel pan, put the ferric chloride into the jar in the pan, and dropped in the first board.
With a jar, you can tighten the lid and do more vigorous agitation than in a tray. Between the shaking and the heat, the process is quite a bit faster than when using a room temp bath and a pan. I forgot to check the time, but it was definitely quicker than yesterday. After the first of today's boards was cleared, I dropped in the second at 10 minutes to 11. This one I agitated even more than the first one, and it was easily done by 11. When it was clear, I rinsed off the boards and headed to the soldering iron.
After wiping down the boards with acetone to remove the adhesive from the vinyl sticker, I tinned the traces to get them ready for the chip, which will be soldered onto the PCB SMD-style.
This technique would be a lot simpler and safer to use with students in your maker classroom than agitating in open trays. Since the chemicals are sealed away inside the jar, there will be much less of a chance of spillage or splashing. Check out the PCB etching article in MAKE, Volume 02 for more ideas and techniques.
If you do it at home, fine, but if you intend to have your students experiment with it be aware that FeCl3 solution decomposes into HCl and Cl2 at high temperatures.
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Thanks for the tip. Warm = good, Hot = bad. We'll use a water bath to bring the temp up a bit, but not much beyond room temp.
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I forgot to say, mechanical action is a terrific way to accelerate etching. In the same vein have you heard of the "sponge" technique ? Makes extremely fast etching with small quantities of FeCl3 (a few seconds). Even works with otherwise "spent" FeCl3. But it is relatively messy.
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