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Thread: DIY Lightbox for UV exposure of PCB boards.

  1. #1

    Default DIY Lightbox for UV exposure of PCB boards.

    Following on from my turned-out-to-be-horrible idea for plotting with Staedtler Lumocolor Permanent red ink direct to PCB's, I turned back to the standard method, as it's really down to what you get to do it.

    Some cheap FR4 double sided photosensitised boards from an Italian eBayer, at a quarter what RS want for similar boards, before they start adding tax or shipping, and an HP Laserjet 5N printer for less than five packs of Press and Peel, and it should be obvious that trying to shortcut the standard produre wasn't really worth it. The Toner Transfer idea is cool, but it is still VERY fiddly, and can't beat the standard method.

    So, cheap printer with AWESOME accuracy, cheap photosensitized boards, leaving just the lightbox as the other vital hardware. Those are NOT cheap. Unless you do it like this:

    A dead scanner. It contains the innards of of a light I found lying beside a vandalised street sign one morning, refitted with the right 11W UV tubes. That's it. I just bent the baseplate to distribute the light better, and stuck a bit of aluminium foil on it to improve the light flood. It even lights up the little indicator light directly by fluorescence so it's easy to know it's switched on when the lid's closed. Sometime I'll maybe add a small timer module, those turn up as junk at times...
    Last edited by The_Doctor; 10-08-2007 at 10:48.

  2. #2
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    Nice ghetto rig. I like it.

  3. #3

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    Quote Originally Posted by carmangary View Post
    Nice ghetto rig. I like it.
    Needs must.
    *bows*

  4. #4
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    Nice work doc.

    Its been a while since I did any boards the photographic way. Nowadays its too easy to pay someone else to do them for me..
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  5. #5
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    Doc I love the scanner idea - I faffed around with home made UV for years and it was a nightmare. In the end I bought a propper unit - which I was lucky enough to be doing a PCB job for someone who would pay for the box - and I have never looked back. The boards I make now are quick to produce and quality - before I wouldnt dare use thin (less than about 3mm) tracks as they wouldnt come out or would all merge together. Changing to proper UV box did it for me but I hope you get results with this - it sure looks like you will.

    Good work - shame about the plotter I liked the idea.

    Rob
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  6. #6

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    Well, I had thought decent laser printers were horribly expensive, and the plotter might be a cheap shortcut. But I decided that the Laserjet 5 was cheap enough and well-reputed enough to get one. Got sent two as there was a problem or two with the first. Both actually work well enough to print some very sharp lines.

    I figured out to use raster, not vector, to avoid errors, and it actually prints faster as a PCB has a LOT of vector for a printer CPU to chew. Better to render it on a computer first.

    Some time I'll probably get nice boards made up but I stand to learn so much more this way, and I'll always want some ease of prototyping. I'm getting too old to do things the hard way, but I need to do this or I won't be able to specify a decent board for anyone else to make...

    The scanner was a nice thought though, I had it sitting around for ages before I realised what I could do. Having realised, it only took a couple of hours to make that box. UV LED's would be nice, but people going that route are saying their $50 spends were cheap. My box will cope pretty well with the small boards I'll be making anyway, it should be good for 3" wide, and I'll usually only want 2" or less.

    I've got some nice lengths of narrow front surface mirror from that scanner too, which might be useful if cut up carefully. Might just send them intact to someone who wants them if they pay postage. They'd form pieces about the right size for Arctos-style beam combining.

  7. #7

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    Anyone know of a matte drafting film that can stand a brief exposure to the 200°C fusing process in a laser printer? Has to be reasonably UV transparent too for photosensitive PCB preparation.

    I've heard of polyester (mylar?) and acetate, there may be others. I've got a bit of some film but I don't know what polymer it is yet. It's matte, and prints better than the intended clear film (which works badly, too many clear spots in the toner), and almost as well as paper but not quite that good.

    I'm considering the fibrous transparencies used for inkjet printers, but that might be too coarse grained to give accuracy, and might not stand the heat.

    Anyone done any experimenting of this kind?

  8. #8
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    Hi Doc

    This is one area where I can probably help you. Take a look at this site...

    http://www.folex.com/prod.php?catp=4...d48ca4df613fc9

    I think this is similar to what I have, it accepts a good image is fully UV transparent and will stand the high temperatures of the laser printer.

    I used to have a small printing company and I used to make my own film positives on a HP4 laserjet. To get a good image you will need to print out in mirror format so that the emulsion (toner) is in contact with your circuit board. If you don't do this the space between the toner and the circuit board will allow the UV light to creep in and you'll lose the sharp outlines.

    I used Folex film for many years and did some ultra fine detail, I was way ahead of my time on this as most printers were still having film negatives made and doing expensive and messy processing.

    The key to success is to get a good thick layer of toner that light can't get through and then to get that film as tight as you can to your plate/circuit board. I used to use a vacuum unit - Google for Parker Countess Printdown Frame - and you'll get the idea.

    If I can be of any further help please get in touch. It is possible i've got some of the Folex that I used to used somewhere. I could probably find an odd sheet to send to you for experimentation.

    Using this film will save you loads of time from wasted efforts as one of the biggest problems was getting a good solid black image on the film, you'll probably already have noticed that if you hold your film up to the light you can see through the centers of the lettering as it's not quite as solid as the edges, you won't get this with Folex.

    Finally, you can buy stuff at printers wholesalers to spray onto the film after you have printed it, this is a black enhancer that REALLY makes the black printed areas very solid, you shouldn't need this though if you go the Folex route.

    Hope this helps you.

    Jem
    Last edited by Jem; 10-14-2007 at 00:18.

  9. #9
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    Very intersting tread this one guys.

    The only thing I can add, is to comment on your question (Doc) about using inkjet printer transparencies...
    When I was on desktop support, I have lost count of the number of fusers I have removed and cleaned out (sometimes scrapped) from laser printers when people have tried printing on inkjet transparencies - so go carefully.

  10. #10
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    Quote Originally Posted by p1t8ull View Post
    I have lost count of the number of fusers I have removed and cleaned out (sometimes scrapped) from laser printers when people have tried printing on inkjet transparencies - so go carefully.
    You shouldn't have this problem with the Folex. I have fed countless thousands of sheets through my trusty old LJ4 and have also used it on many newer printers since then, the latest being my Oki C5400 colour.

    If you're worried about trying it on your own printer, send me a (preferably .pdf) file of the circuit board and i'll print it out onto folex for you to try.

    One other thing, the Folex used to be about .50 pence a sheet and it comes in boxes of 100 sheets, here is the spec' off the box...

    Name: Laser Film Matt
    ANKEY: 0969.5.440
    Gauge: 0.090

    It's a couple of years or so since I bought any so it may be a good idea to check the current price.

    Cheers

    Jem

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