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Another Wacky Idea for Making Circuit Boards Part 2

Discussion in 'Electronic Design' started by D from BC, Jun 7, 2007.

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  1. D from BC

    D from BC Guest

    How about this for exposing PCB's?

    1) Take a LCD monitor apart and replace its backlight with UV tubes.
    2) Display a black and white image on the monitor.
    3) The presensitized PCB is placed on the monitor for exposure..

    I don't know too much about LCD displays. Could something like this
    work?

    It might very useful for a PCB fab house..
    D from BC
     
  2. John Larkin

    John Larkin Guest

    I suspect the resolution would be very poor. Put a thin piece of
    frosty mylar or paper on your monitor... the image is pretty blurry.
    And the LCD polarizers and such may not work for UV.

    John
     
  3. Fred Bartoli

    Fred Bartoli Guest

    John Larkin a écrit :
    UVs will toast them pretty quickly.

    D, why so much energy wasted in wacking ideas when today you just have
    to provide some low cost PCB mfr with gerbers and let them work. Just
    get real.
    Oh, I can see some thread about a wacky idea on how to glue excel to
    some video player and hack your own CAD program.
    Then you just have to build a CNC drill, hacking an old sewing machine
    with some old printer stepper motors...
     
  4. D from BC

    D from BC Guest

    Oh bummer :(
    It's just that I'm always changing my designs (f*ck ups) and my PCB
    volume is like 20 boards/year..
    I think I've never duplicated a PCB yet..
    I have one PCB where I did so many design changes that if someone
    copies the design ..that's a laughable amount of useless electronics
    that I just isolated instead of removing..

    So I don't mind DIY PCB fab for now.. Let's me get stuff done on the
    weekend when PCB fab houses are closed. :)

    By the way..
    I've ordered dry film photoresist to play with for the 1st time. :)
    D from BC
     
  5. Jasen

    Jasen Guest

    prolly not... maybe you could use the optics from a laser printer
    instead... dunno what wavelength they use or if visible light
    photoresist is available.


    Bye.
    Jasen
     
  6. I'd expect the liquid cristals to absorb
    ultraviolet at which the chemical bonds
    may even break. As Fred put it : The UV
    will toast the liquid cristals.

    A simple solution is to use an polyester
    foil in the printer. I prefer the laser,
    but a colleague successfully applied an
    ink jet too. Just make sure to have the
    top layer mirrored, such that the ink is
    right on the photosensitive copper surface.

    Rene
     
  7. Jim Yanik

    Jim Yanik Guest

    You can BUY cheap battery powered small fluorescents at Lowes,WalMart,Home
    Depot,for ~$10,some also use 12V AC adapters. (I use them for emergency
    lighting in blackouts)

    Then get a UV sterilizing tube for it,leave the cover off.
    I used to use one for erasing EPROMs.
     
  8. John Larkin

    John Larkin Guest

    It sounds like you'd do better investing energy in getting it right
    the first time, instead of finding a speedier way to iterate mistakes.

    Most of the things we design are sellable as Rev A, the first board,
    and we don't prototype. As complexity and density and board layers go
    up, time spent checking really starts to pay off.

    John
     
  9. Gary Tait

    Gary Tait Guest

    Might not work.

    If a fab house were to do it optically, they'd use mylar sheets with the
    pattern printed on to do a silkscreen, which they'd use to screen etch
    resist or powered/liquid conductors on a PCB.

    For one off optical, they could use the mylar sheet, or a transparency
    from laser or a plotter.
     
  10. John Larkin

    John Larkin Guest

    Nobody I know of screens boards these days. The bare copperclad board
    is cleaned and roller-laminated with a dry resist. The board is
    sandwiched with the artwork film and exposed to UV, which sensitizes
    (actually polymerizes) the resist. The resist is then "developed",
    which removes the unpolymerized areas of resist. Then the copper is
    etched.

    I suppose some people still use liquid/baked-on resist, but the
    process is pretty much the same.

    Silkscreens have very bad resolution, so could be used only for very
    crude boards.

    I wonder if any direct laser-scan exposure is being done, to eliminate
    the film.

    John
     
  11. D from BC

    D from BC Guest

    I think I've seen UV lasers in my internet travels.

    I'd be happy with a slow moving low power laser on an XY plotter or
    CNC :)

    My optics are crappy..but I think it'll work. The PCB copper might
    need to be buffed to a mirror finish before the photoresist is put on.
    D from BC
     
  12. Selected by John Bordynuik "Nobody I know of screens boards these days. The
    bare copperclad board
    is cleaned and roller-laminated with a dry resist. The board is
    sandwiched with the artwork film and exposed to UV, which sensitizes
    (actually polymerizes) the resist. The resist is then "developed",
    which removes the unpolymerized areas of resist. Then the copper is
    etched."

    I see many automotive single and double-sided board manufacturers still use
    silk-screening. In fact, a shop I was at a couple of weeks ago is continuing
    to use it on flex circuits. Screening has improved much....

    P.S. I wouldn't use it - photo is better but more expensive.

    Regards,

    John Bordynuik
    CPU Architect
    JBI
    http://www.johnbordynuik.com
     
  13. D from BC

    D from BC Guest

    Long ago I tried to find silk screen...screen material...another
    GoogleFu battle that I lost.. :(
    D from BC
     
  14. D from BC

    D from BC Guest

    doh! :eek:

    What's some good keywords to find that stuff?
    silk screen screen?
    printing screen?
    screen for printing?

    "I scream for silk screen" :p
    D from BC
     
  15. ?? You just have to know that silk screens are not made from silk.

    ;-)


    Best regards,
    Spehro Pefhany
     
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