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Photo-etch light source?

Discussion in 'Electronic Basics' started by Usual Suspect, Mar 4, 2007.

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  1. MG Chemicals sells pre-sensitized copper-clad PCB blanks for use with their
    exposure and etch kit. Pretty straightforward "print pattern on transparency;
    place on PCB; expose to light; wash off exposed portion; etch" process.

    The "expose" part of this process consists of using MGC's "daylight"
    fluorescent lamp.

    If it's truly a "daylight" bulb, wouldn't direct sunlight work for this
    purpose? I presume this bulb is of a particular wavelength. What is it?

    Any other ideas to use this process to etch PCBs without their lamp?

    Thanks,
     
  2. I use sunlight to expose all my boards. The only difficulty
    is waiting for a clear sky, so the exposure is predictable
    and the edges are sharp.
     
  3. John Barrett

    John Barrett Guest

    "daylight" flourescents are easy to get at your local home store -- as are
    the fixtures to run them -- buddy of mine used just one... but had some
    problems with fuzzing that I think would have been solved had he used 2 or 3
    for a more even light source -- making an exposure box with 2 or 3 lamps --
    the ones about 12" long, and a piece of plexi as the exposure surface is
    pretty easy.
     
  4. Waiting for a clear sky may take days or even weeks in this part of the
    world. Even then exposure time is a long shot. So for years I used a 120W
    high pressure mercury bulb, meant for streetlighting. It not only produced
    enough UV, it also produced a lot of visible light and even much more heat.
    So last year I got an obsolete A4 flatbed scanner and an old home solarium -
    "face browner" - and build a new exposure box. Works like a charm so the old
    one is for sale now :) The idea of the new exposure box is not new. Look at
    http://gathering.tweakers.net/forum/list_messages/730455
    The text is Dutch but the pictures are universal.

    Exposure time is 2 min. Make sure the traces on the transparency are pitch
    black. I always stack two of them as one lets through too much UV and makes
    the etched copper look like a rats dinner.

    petrus bitbyter
     
  5. Tim

    Tim Guest

    Stack 2 of them eh? I never thought of that. I used a tanning bulb for
    exposing the board when I did that stuff. I built an exposing table with
    a timer that kept the bulb on for 15 minutes. It had the timer built
    into the table, and a piece of soft wall conduit that supported the lamp
    so it was 12" from the board surface. Worked great too! Probably would
    have been more reliable using 2 transparencies.

    I have since switched to the photo paper method published by Thomas P.
    Goote, and I find very reliable and sufficiently accurate for my needs.
    FYI, I use ammonium persulfate to etch the boards I make. Check out his
    web page here; http://www.fullnet.com/~tomg/gooteepc.htm

    Have fun!

    - Tim -
     
  6. Sure, 250W photolamp at 30cm distance for 8 minutes.
    Except for DownUnder, where these lightbulbs will be illegal soon.
     
  7. Barry Lennox

    Barry Lennox Guest

    I don't know about the MG system, but I have used sunlight a number of
    years ago. It works well, the only problem is that it's variable
    depending upon cloud cover and the time of year. Experiments are
    needed to get the exact exposure.

    I now use a Philips TUV 20 flouro lamp and it works fine. However, it
    is a short wavelength UV and the radiation is considered a little
    hazardous, I just take care to only switch in on when the artwork is
    all set-up and everything is covered.

    Barry
     
  8. Ecnerwal

    Ecnerwal Guest

    I've used a 100W mercury vapor lamp, up close and personal. Most of the
    resists are looking for some UV component. A metal-halide fixture will
    probably also work well, a sodium vapor light probably would not. 175W
    is probably easier to find than 100W, that just happened to be the lamp
    I had handy at the time.

    A carbon arc would be just dandy, and could offer some old-fashioned
    electro-mechanics for a bit of variety in your projects.
     
  9. Lionel

    Lionel Guest

    Yes, but it's very hard to get an accurate exposure with sunlight.
    I've heard that greenhouse fluorescent tubes (the kind used for
    hydroponics) work okay, but I don't have any personal experience with
    them.
     
  10. I wonder guys, why wouldn't you just use a proper long-wave UV bulb? They
    are aplenty and dirt cheap... Any T8 BL or BLB works like a charm, doesn't
    require anything but regular fluorescent ballast to run and produces that
    very sub-400nm lightwave required for exposure...

    Why are you trying anything but a proper tool? Am I missing something?

    Just FUI -- that magical MGC lamp is just a 15 Watt T8 BL bulb in a regular
    fluorescent fixture...
     
  11. Bob Masta

    Bob Masta Guest


    If you want to stick with photo-resist methods, the simplest
    approach is to buy a "tanning" lamp. Mine looks like a standard
    floodlamp, with a dimple in the center. Puts out plenty of UV,
    way more than direct sunlight (at least here in Michigan!) and
    it's consistent even on cloudy days. <g>

    Now, I should add that it's been a "few" years since I bought
    this (20 or more) so they may not be so readily available as
    they once were. Even back then, it was pretty clear that
    tanning was not such a smart idea. Now, you'd have to be
    pretty crazy or illiterate to do it... which means only 99% of
    students and only half of the voting public. ;-) So the
    market and supply for these may have slacked off a bit.

    Best regards,




    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
    Scope, Spectrum, Spectrogram, Signal Generator
    Science with your sound card!
     
  12. Guest

    Guest Guest

    i used a Gralab photo timer with a single 200 watt standard incandescent
    about 3 feet above the bench.

    standard safelight was handy also.

    i tape the film onto the pc board. then a single sheet of window glass
    weights the film/pc board flat.

    after 25 yrs, no problems.

    time to expose ? always went with about 4-5 minutes. it depended on the
    ants in my pants. critical it is not,

    the solvent bath later i found was the real problem with leaving in too
    long.

    i always used photo filmed positives, very precise and failsafe.
     
  13. i used a Gralab photo timer with a single 200 watt standard incandescent
    Nothin' could be simpler...
    Now, that's a tome of data!
    OK. I won't be a "clock watcher".
    You mean the chemical for removing the exposed photo-sensitive stuff from the
    PCB? Don't you just submerge it and brush it and watch when it's all gone
    (all the exposed part) then take it out? Or am I missing something?
    You're talking about the transparency? I hear that output from a printer is
    good enough. No?
     
  14. Grostle News

    Grostle News Guest

    Manufacturers of fluorescent light bulbs provide wavelength and light
    intensity data for their products. If you have the bulb stock number try
    putting this into google search engine. The retailers of light bulbs
    sometimes have product info sent to them by manufacturer. Catalogs used
    by retailers for ordering may have such info. You can always write to
    the company manufacturer to get product specifications.

    There are other applications using bulbs for photo light or chemical
    reactions. Some types of silk screen processes use exposure bulbs.
    Diazo-blueprint photo process uses UV light bulbs. E-prom devices use UV
    to erase content. UV bulbs are used in medical applications for
    sterilization.

    If you get a bulb but need a fixture you can use a screw-in energy
    saving fluorescent light bulb.
    In my area these screw-in energy savers cost less than a dollar. I
    removed the bulb from one of these then replaced it with the fluorescent
    bulb I wanted to operate. I made sure the wattage ratings for both were
    nearly the same before I started. The re-wiring should be as short as
    possible. Be careful and don't forget that fluorescent bulbs run on
    higher voltage.

    btw- I have replaced all incandescent lights in my apartment with the
    screw-in fluorescent fixtures and have seen a significant savings in
    electric bill.
     
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  16. Guest

    Guest Guest

    the developer/xylene (or whatever it is) i never made any mechanical
    brushing or other attempt to force the residue to release any faster than
    the dissolving rate.

    my problem originally was i left the exposed board in way tooooo long and
    the light fixed resist actually did disssolve eventually, perhaps 20
    minutes! way too long

    stick with the manufacturers recommends

    i always did a second wash in fresh developer to remove any trace residual.

    then after it had completely dried/evaporated, it went under some cool then
    warm water with small amt of detergent (actually any wetting agent will do,
    the blu stuff used in automatic dishwashers is cheap and easy to find)
    before it went into the etch bath. that seemed to make the etch time
    consistent across the entire board.

    yes, the transparency may be made with printer, i have used a good 600 dpi
    laser printer (overkill actually) but 300 or even 150 dpi will do.

    vellum is usable, overhead mylar film is better, plain paper is good for
    crude stuff

    my only hazard with that was the 200 watt bulb often melted the toner and
    screwed up the board. so i switched to using photo exposed
    negatives/positives. it takes longer, but results are far superior and the
    physical stability of the film always gives u the same dimensions EVERY
    TIME. thats assuming u make it a proper size initially! detail and
    resolution are superior also.

    short runs of less than ten units, i usually winged it with the printer
    though.
     
  17. Grostle News

    Grostle News Guest

    BTW- If you ever need to measure light intensity directly, such as
    lumens/candela etc it is possible to do this with the built-in light
    meter most 35mm cameras are equipped with. I did this many moons ago so
    I don't recall the details.

    Here is an explanation I just now found in google about the procedure,
    just in case any one is interested:

    http://fins.actwin.com/aquatic-plants/month.9711/msg00049.html

    saxum g.n.
     
  18. Grostle News

    Grostle News Guest

    Safety reminder: If you use Xylene don't forget that this liquid is as
    flammable as gasoline. Vapors of xylene from an open container or an
    evaporating source can crawl invisibly and without detection of it's
    odor to an ignition point (pilot light, static discharge, electric range
    etc.)

    Xylene should be used in a well-ventilated area nowhere near any flame
    or possible spark.

    saxum g.n.
     
  19. Lionel

    Lionel Guest

    Good tip. That should work fine with more modern - even digital - SLR
    cameras, as long as they have a full manual mode, eg; any Canon or
    Nikon DLSR. The only problem is that the table in that post is for
    ASA/ISO 25, which isn't available on many DSLRs. Fortunately, that's
    easy to correct, by converting it for ISO 100 (2 stops faster), which
    most DSLRs have, then shifting the shutter speed by 2 stops to
    compensate:

    *OLD* ASA/ISO 25 @ 1/60:
    f-stop foot-candles
    2 100
    2.8 200
    4 400
    5.6 800
    8 1,600
    11 3,200

    *NEW* ISO 100 @ 1/250:
    f-stop foot-candles
    2 100
    2.8 200
    4 400
    5.6 800
    8 1,600
    11 3,200

    Please note the comments about metering on white objects vs green,
    etc, in the original post at that URL.
     
  20. Bob Masta

    Bob Masta Guest

    The problem with this approach (regarding the original photo-etch
    topic in the subject line) is that it only applies to visible light,
    whereas photo-resist is sensitive to UV, which is greatly
    reduced by camera lenses.

    So, you can't use this to make any sort of absolute measurement
    of UV levels, but if you have a source that emits a broad spectrum
    (like a tanning lamp) such that you can get a reading on the meter,
    then it would probably be reasonable to assume that everything
    scales properly. Thus, if you use that same source at a different
    distance, the camera meter could tell you the *change* in
    exposure.

    Best regards,


    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
    Scope, Spectrum, Spectrogram, Signal Generator
    Science with your sound card!
     
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