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Old 31st October 2013, 03:49 PM   #1
00940 is offline 00940  Belgium
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Default PCB fab - what worked for me

Nothing revolutionary... actually I'm writing this as a reference for myself. If it can help others, that's a bonus

The tools:

- photoresist blank pcb, from Bungard
- developper, Sodium hydroxide from Kemo
- etchant, fecl3
- three plastic boxes, one a bit bigger
- one UV nail curer, 36W (4 tubes), plenty on ebay for cheap, the bottom drawer removed
- rubber gloves

Procedure:

- The day before etching, print the layout on normal paper. Then, pour a bit of olive oil on it and rub over the layout. Remove the excess oil and let dry during the night.

- Start the UV machine

- Cut the paper and the blank pcb to size while it preheats

- In a dark room, remove the protection film, put the mask over the pcb and expose for about 7min (I put the pcb and the mask in a cd case to keep them close)

- During exposure, prepare the developing bath in a first plastic recipient, inside the sink. Starting now, put on rubber gloves and protection glasses, caustic soda is hazardous ! 1 teaspoon of caustic soda for 25cl of water (just using cold water from the tap). Mix well.

- When the pcb is exposed, develop. About 20sec is fine. The developer is a tad strong, most of the reaction will happen very quickly. Shake a bit the pcb in the bath to properly finish it. Don't scrap it though.

- If you're not doing other pcbs, flush the developer down the drain with a lot of water.

- Dry the pcb and prepare the etchant. Pour boiling water in the bigger box, put the second plastic recipient in the boiling water and fill it with enough fecl3 to easily cover your board. The etchant needs to be warmish, otherwise the process takes way too long and the resist will start to fail. Careful, wear old clothes, the etchant destroy fabrics and colors everything it touches. I do this outside for these reasons and to avoid the fumes.

- Dump the pcb inside the etchant and move it around (a wooden fork is handy). When done, rinse and dry.

- For now, I put the etchant back into the bigger bottle. I've done quite a few pcbs with it and it doesn't seem to lose bite too quickly. When it goes weak, bring the bottle to a waste collection center. Not a good idea to dump copper ions down the drain.
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Last edited by 00940; 31st October 2013 at 03:53 PM.
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Old 9th December 2013, 06:59 AM   #2
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Thanks for the info, I will try it out on a small scale board next time the need arises.

My favorite things are "things that work". Sharing them with others can help in "cutting to the chase" and save time, money, and frustrantion. I have too much of the latter and too little of the first two!
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Old 9th December 2013, 07:51 AM   #3
Did it Himself
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I'm assuming that you used a laser printer. I don't think an inkjet print would cope well with olive oil.

Did you try transparancy film? I have an inkjet and HP's own film has always worked well for me (on best quality setting).
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Old 9th December 2013, 10:32 AM   #4
00940 is offline 00940  Belgium
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I indeed use a laser printer.

Didn't try transparency films. It's widely known to work though. But I'd have to re-run calibration tests for the exposure time. I'm a bit lazy ;-)
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Last edited by 00940; 9th December 2013 at 10:40 AM.
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