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PCB manufacturing with a LCD layermask, possible?

Posted by ElectricMucus 
PCB manufacturing with a LCD layermask, possible?
August 14, 2011 05:42AM
I just had an interesting idea:

Producing PCBs still is a process where "rapid prototyping" uses the same techniques as mass production does. Layer masks are still made and the whole process is inherently better suited to produce several copies instead of one.
Furthermore the need of physical layermasks increase the cost of small production values tremendously.

Recent TFT diplays offer very high contrast ratios already and provide decent resolution.

The thought is to replace the layer masks with a LCD screen, possibly modify a consumer TFT display to use a UV Lamp instead of the fluorescent back-light.
What do you think, is this a viable idea? Would the contrast archived be sufficient for ultraviolet light?
Re: PCB manufacturing with a LCD layermask, possible?
August 15, 2011 08:32AM
Erm ... now you have than light on your workpiece, how does that make a PCB from it?

If you're talking about photo-sensitive etch resist, I think such masks are simply used because they're the cheapest variant. Projecting the light with a projector whould also work, but is more expensive.


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Re: PCB manufacturing with a LCD layermask, possible?
August 15, 2011 04:21PM
Well, yes exactly.

Aren't layer-masks rather the only variant? My point is while of course the initial costs would be higher (probably not if you consider the prices of commercial UV-lightning apparatuses) but the costs for the developing would be free.
Also making double layer pcbs is a hassle doing it manually and the process could be automated easier.

I'm not saying this would be the oh-so perfect solution just something I think is worth trying out some day. smiling smiley

A projector would be fine and a pcb holder for a overhead projector could be easily printed.

Calibrating this thing might be difficult since the lens distortion must be accounted for.
Any ideas?
Re: PCB manufacturing with a LCD layermask, possible?
August 16, 2011 11:38AM
If i understand correctly, you want to stuck a tft with the proper black&white image against the copper cald (uv curable), to create the image. I suppose its not a bad ideea, but i doubt it would be worth it economically. I think there is a chance that tft light might cure it directly (i think it might, but maybe in about 1000's the time it would with plain uv neons or street lamps broken bulbs).

But i would be worried more about the mechanical aspect. If you use a transparency you put it on the board and 2 pieces of glass each side so it will press against each other and no light will ever come under the black areas. I dont see how you can press the tft screen against the copper cald, or properly block the light under the black for that matter. I think the tft has a slim membrane that will pass the light into the black areas anyway ... or you might even break the tft if you press too much.

If you just want a single board or a few boards, for the sake of simplicity you can:
1) use toner-transfer (down to tqfp pins) or
2) print the image on transparency and put the board on the window for a day - the sunlight will contain UV component and will cure it eventually, just in much more time than a few minutes. Do some tests and its cured when you can see the image with naked eye - just a slight difference like a shadow - you'll see.

Anyhow: Good Luck!
Re: PCB manufacturing with a LCD layermask, possible?
August 16, 2011 11:45AM
If you just want a simple uv box, i would either: 1) use some disco-type neon lamps or 2) take a street light bulb (the sodium or mercury ... etc), and break its glass, although be warned that the second option may produce some dangerous stuff and also you should never look directly into it or you might remain blind for the rest of your days. No joking with it. By all means stay away from 2), just mentioning it so you know its there as option and still dangerous if you encounter it somewhere else presented in a better way.
Re: PCB manufacturing with a LCD layermask, possible?
August 16, 2011 12:54PM
And just as a note, photo method is not cheapest, i think cheapest is toner transfer. Photo transfer is more "pro" in the terms it can achieve easier a much better resolution and finer traces, but its more expensive in comparison:
1- need of either transparency or "transparency" spray for normal printer A4 paper.
2- special uv copper calds (or the spray that can be used on normal cald),
3- usual UV box for speed&double sided or if 1-sided, leave it near the the window for ~6-12hrs (day).
4- also contains an extra "developing" phase but the developer is cheap by itself and even can be made with kitchen ware.

For DIY perspective, both require a good printer and consumables. Also a note, if toner transfer does not work with a certain laser printer its 90% probably because the cylinder is at the end of its life and doesnt drag enough toner on the sheet.

The real advantage of photo transfer compared with toner transfer is that is does not need heat at all. Heat will affect the cald itself, just a little, and somehow traces of same width, can lift off easier if the board is done with toner transfer than otherwise (my impression at least). But this is same thing also (or even more) affected by the quality of substrate. Also most of UV curable copper calds are proper quality FR4 while normal copper calds are usually the cheapest versions possible, which aggravates the aspect. An extra buck for a good copper cald for DIY is well worth it. Cheap copper cald mostly sux for DIY tbh, not a real economy to have half of the board soldered and have one trace coming off right at that point - all in the name of an 0.5eur "economy".

In the end, the photo method can make traces smaller than toner transfer. Although either way i dont trust very slim traces for diy, so would rather just edit the pcb source file and widen the traces as much as possible, which also makes the toner transfer trivial and safe enough. Pretty much same as photo just even simpler.
Re: PCB manufacturing with a LCD layermask, possible?
June 21, 2017 11:07AM
I have made PCB with LCD layermask
see: https://youtu.be/hczjN9er9TI
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