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Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
Hi. This thread documents my attempts to build a PCB etcher using a Sweex digital picture frame, a LOT of SMD UV LEDs (only way to get reliable light spread without a lossy diffuser), an old touchpad pcb with the plastic removed, and some ingenuity.
I chose this particular frame because among its other features it has the ability to "stick" on one picture without doing that annoying frame transition thing which others do, so staying stable for 15 minutes is no problem.
started building the LED panel, unfortunately ran out of micro gauge solder so will need to obtain some more.. any ideas?
as you can see the picture quality is excellent for a £7.99 device, even though the colour may be a problem i hope to get around this using some very basic image editing.
Comments?
-A "Bother" said Pooh, as he misspoke the words and the Army of the Dead awoke..
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
You're an ingenious fellow, Andre!
The other day, I noticed I had a bottle of potassium dischromate on a shelf that I hadn't looked at for a long time, which put me in mind of the 'gum dichromate' photographic process, which might be of interest to you.
K2Cr2O7 is sensitive to light - though not nearly so much as silver halides - but nonetheless was used widely in early photographic printing, and until much more recently in the photo silk screen printing process. In brief, a paste made from the dichromate and any of a number of colloids will become hard when sufficiently exposed to strong light - forming a mask - whilst the unexposed areas remain soft and are readily washed off.
It goes without saying that hexavalent chromium compounds are known carcinogens, so steady as she goes.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
heh..
another thought, the uv reacting glue sold for repairing windscreen chips and cracks might harden if heated up to about 30C and exposed to UV from something like this.. could be a low cost alternative to expensive resist coated boards..
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Conundrum wrote ...
heh..
another thought, the uv reacting glue sold for repairing windscreen chips and cracks might harden if heated up to about 30C and exposed to UV from something like this.. could be a low cost alternative to expensive resist coated boards..
I believe there's quite a range of UV engineering adhesives, though I have no experience of them.
Registered Member #2814
Joined: Wed Apr 21 2010, 12:28PM
Location: Scotland, UK
Posts: 24
Screen printable UV curable inks are available, even solder resist. You just flood coat the board, oven dry it and expose to UV. Problem is they're about £70 a litre from Mega and I haven't as yet found a cheaper source.
What kind of resolution / board size do you anticipate it will be capable of?.
Registered Member #2814
Joined: Wed Apr 21 2010, 12:28PM
Location: Scotland, UK
Posts: 24
It's Conundrum, he's not usually an abrasive poster
The display glass will be quite thin, it will attenuate the UV but hopefully not by a significant amount. Avoiding a lossy diffuser may provide enough to compensate for the loss through the display.
Registered Member #3040
Joined: Tue Jul 27 2010, 03:15PM
Location: South of London. UK
Posts: 237
Kilham wrote ...
It's Conundrum, he's not usually an abrasive poster
The display glass will be quite thin, it will attenuate the UV but hopefully not by a significant amount. Avoiding a lossy diffuser may provide enough to compensate for the loss through the display.
It doesn't take a lot to attenuate UV significantly. When I built my double sided exposure box I found I couldn't get acceptable exposure on both sides due to the fact that the mylar pulldown sheet on the top side was attenuating the UV more than the bottom side (no mylar) so I had to add a mylar sheet to the bottom side just to balance the light levels. I hope the LCD does work but I also hope the basic principle was tested with a small display first before spending too much time/money on it? Personally I use Inkjet transparencies cheap and easy.
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Digital picture frame PCB etcher
