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Home made PCB's.

Discussion in 'Electronic Basics' started by Richard, Nov 14, 2009.

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  1. Richard

    Richard Guest

  2. It would be better if you got your transparency professionally done. It
    comes out almost completely opaque and generally higher resolution with no
    smudging unless the handler is a moron(happened to me once).

    Some things to add to your process:

    1. Create a copper pour. This makes copper etching faster and wastes less
    etchant as you only are removing the copper required to create traces.

    2. For very fine pitch traces/pads you want to make sure your transparency
    is printed so that the printed side is against the copper. This reduces the
    gap which actually can cause finging effects.

    3. Generally put the photo mask on for longer periods of time. The boards I
    have say for about 8m but I've done tests between 8m and 30m and the all
    produce about the same results but closer to 8 and you risk not removing all
    the mask which creates problems and generally requires more resist removal
    time or stronger solution.

    4. Use warm water for photomask removal solution. It can speed up the time
    greatly(from mins to seconds) and seems to produce a more crisp image. (I
    generally keep a bottle of concentrated solution that I mix when needed)

    5. Copper eching technique and time is very important for getting very fine
    pitch. Agitation is necessary because it helps create a more uniform etch.
    Heat can make a big difference. If I'm not doing super fine pitch stuff I
    generally just leave the board in for 30 mins or so then go agitate by hand
    a little. Agitation and heat require more supervision.

    Probably the biggest thing though is the mask and proper photoresist
    removal. This is why I just run down and get a mask made for about $1.
     
  3. stan

    stan Guest

    Are you talking aboutsomethng like Kinko's here or do you use someone
    who handles electronics stuff?

    I've always just DIY. Do you provide somethng like a PS/PDF or some other
    electronic format or do you provide paper?

    Lately I've been wondering about finding some low volume vendor to
    just do the whole thing but I haven't really spent much time looking.
     
  4. I go to office depot. It's about 70c and I simply take a usb drive. They do
    the rest. You need to tell them to print at the highest quality and dark as
    possible. The format is pdf.

    I'm not sure how much better it is than DIY I simply find it easier than
    worrying about the ink jet method. I've had success with it but the quality
    is less.

    You might need to tell them not to get fingerprints on the transparency and
    only to handle it by the edges as it will ruin it. I believe if you are not
    satisfied they will redo it for you for free. Once I did get fingerprints on
    one but it wasn't too bad and was able to fix it with a permanent marker.

    Here I'm only talking about the transparencies and not sure if you mean the
    whole pcb process or not. I do the pcb's myself(of course not the making the
    pcb itself) except in some cases when the boards are very large or require
    many.

    If you have such a place close that can print the transparencies for less
    than a dollar it is probably worth it as the ink jet method does require a
    lot of ink(if you use copper pours), special transparency pages that are not
    cheap, and the quality is nto as good.

    Also the inkjet transparencies use an adhesive so the ink and stick to the
    page and this does degrade quality.

    Now your pcb has to fit within a 8x11 page of course...
     
  5. Hammy

    Hammy Guest

    I could never understand why people etch off all the copper use it for
    a trace. Unless you are doing matching (Z) use the copper for a low R
    trace or for ground.

    I've been using the toner transfer method for dual sided boards. This
    is much cheaper and less time consuming then UV exposure.

    http://www.dr-lex.be/hardware/tonertransfer.html

    When working with fine pitch components you have to watch the pressure
    on the iron so you dont smudge your pads.

    I do dual sided boards and use surface mount almost exclusively . I
    hate to drill and SM has more desirable traits reduced parasitic's and
    size to name a few.

    [snip]
     
  6. Richard

    Richard Guest

    The toner transfer method looks interesting, what's it like for very fine
    traces and close pads (SMT)?
     
  7. Hammy

    Hammy Guest

    I just finished an AD9834 dual sided board the AD9834 comes in a 20
    lead TSSOP with 0.65 pitch. 0.65 is pretty common for dual bjt's
    etc.SC-88 (SOT-363) I use these pretty regularlily traces to 8mil's.

    With additional care finer pitches and traces should be possible. You
    just have to be careful with the pressure you apply with the iron. If
    you use to much you can widen the pads /traces. It just takes a bit of
    practice like everything else.

    Before I etch I'll go over the board and look for any possible shorts
    (Ink smudges) and correct them if required with a tiny sharp
    screwdriver. I rarely have to do this anymore.

    I also use a minimum etch. This saves on etchant and time. It also
    makes the boards more durable for soldering / de soldering.
     
  8. stan

    stan Guest

    Got it. I used to teach and we outsourced once in awhile but I never
    really noticed any special quality advantage; hence I asked the
    question. Your idea clearly has merit and I may give it a try.
     
  9. Clint Sharp

    Clint Sharp Guest

    I got some transparency film that was designed for use in laser printers
    from Farnell, excellent stuff.

    http://uk.farnell.com/mega/100062/laserstar-film-a4-10-sheets/dp/895945

    With a genuine HP cartridge I had no problems making PCBs in a small
    production run (around 60 boards because we couldn't get them off the
    PCB house quickly enough).

    Things to remember are that you need to use fresh PCB stock, put the
    toner side of the film against the etch resist laminate because you get
    a sharper image, turn off RET on the printer (sharper image) and make
    sure the driver is set for best quality.

    I've prototyped TQFP and SOIC using that film with no major problems,
    the problems I did have were caused by old PCB stock and a dodgy
    refilled cartridge in the printer. I may have a go at a PCB for some
    AD9851 chips I've been hoarding for a couple of years now.
     
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