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Bubble etch tank - first board

Discussion in 'Electronic Basics' started by Melodolic, Jun 15, 2006.

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  1. Melodolic

    Melodolic Guest

    Just made my first PCB using the bubble etch tank I made last weekend.
    Photos and associated ramblings at...

    http://lab.melodolic.com/index_PCBEtch.php

    This was done using the Press'N'Peel laser printed transfer film sold by
    Maplin in the UK. The process is about as simple as can be: print the
    pattern, heat the board-and-film sandwich, peel off the transfer, etch the
    board.

    It certainly seems to work, although I can't say my first result is pretty.
    That said, I may have over-etched somewhat, with the result that some of the
    resist was undercut.

    The etchant I used was the powdered Sodium Persulphate from Maplin (4ukp for
    enough to make a litre). Using it was no problem at all - only took a few
    seconds of stirring with a plastic rod to dissolve most of the powder, and a
    few seconds more in the tank with the air running sorted out the rest. I
    liked the fact that this stuff is almost as clear as water - very easy to
    see what was going on. Looking at the bottle, I notice that now has a slight
    blue tinge - something to do with the copper absorption?

    I got the temperature wrong when I mixed up the water, with the result that
    I had 35 Celsius rather than the 50 I was after. I put the lid on the tank
    and stuck it in the microwave - about 2 minutes at 1/2 to 3/4 power (in 20
    second bursts with temp readings taken each time) brought it nicely up to 50
    degrees. The aquarium thermometer was over-reading by 2-3 degrees compared
    to the digital thermometer. By the end of the etching session (say, 15
    minutes in total), the tank thermometer showed a drop of about 4 degrees.

    I found that the board moved around quite a bit in the tank, and had settled
    such that some of it wasn't getting hit with the bubbles - after about three
    minutes, one half of the board was clear, while the other was still covered
    in copper. Jiggling it about about a bit had the remaining copper removed in
    another minute or so. I think I'll try some different basket designs, and
    maybe come up with a way of stopping boards sliding about.

    Overall, I'm very pleased, not simply because the Press'N'Peel seems to have
    worked at the first attempt, but because this is the first PCB I've ever
    made! :)

    The home-brew bubble etch tank seems to work a treat - just need to come up
    with a better basket. Handling the tank was fine - tipping it up to empty
    the etchant into a container was easy, and the airstone retainer did its job
    perfectly.
     
  2. Guest

    What are you talking about! That board is beautiful!

    Congratulations on your first board!

    Michael D.
     
  3. Melodolic

    Melodolic Guest

    Thanks. :)

    Drilled and populated it last night - amazingly, it worked first time!
     
  4. tombiasi

    tombiasi Guest

    You got an "A".
     
  5. Take your time my freind the first time is never easy,if you don't
    sucseed first time round addopt a different approach,maybe try dropping
    the tank temperature,using adifferent etchant or maybe change to a
    different etch resist,there is always hope,keep up the passion,from
    some one who cares,regards," roundle01"
     
  6. Nice work!
    I think it's about time I got myself a bubble etch tank, been using a
    flat tray for 25 years now! Not much fun shaking that tray back and
    forth...

    Dave :)
     
  7. Melodolic

    Melodolic Guest

    It was the prospect of tray wobbling that got me started with the tank. I
    originally went out to look at a possible mechanical means of wobbling the
    tray around (looked at motors and cogs in Maplin), when I saw the plastic
    box that was to become the tank. After that it was all just "that looks
    about right" on-the-hoof specification of parts as I wandered around the
    various shops (Maplin, pet shop, garden centre). Came together rather
    nicely, I reckon. :)
     
  8. joseph

    joseph Guest

    You can also use the press-n-peel blue to make a nice (black) silkscreen.
    Just make a second P-n-P "template" of your silk screen image...remember to
    mirror image it! Iron it on the top side of your PCB. Coat with some
    acrylic spray and presto. Do this BEFORE you drill otherwise you won't be
    ablt to iron the P-n-P onto the rougher drilled surface.

    Also... use a very small inner hole size for your vias. This will let your
    drill bit 'find' the center easily. The drill bit will of course open it up
    to the proper size.

    jj
     
  9. joseph

    joseph Guest

    oh, almost forgot...

    You don't have to waste a whole sheet of P-n-P just to print a small board:
    1) Print your image on plain paper first.
    2) Cut a small piece of P-n-P that is slighly bigger (1") than that image.
    3) Scotch tape the P-n-P (dull side up) onto the plain paper, tape it right
    over the printed image. Use ONLY one piece of tape along just the "leading
    edge" of the P-n-P otherwise you get a wrinkled mess.
    4) Manually feed the paper back into the printer ("leading edge" first) and
    print again. This time the image will be printed on and lined up perfectly
    on the small piece of P-n-P.

    jj ...doing .5mm trace spacing work with P-n-P blue!

     
  10. Melodolic

    Melodolic Guest

    That's a good idea. I didn't use a whole sheet, but did three prints of a
    small board along the width at the leading end (the board size was a good
    fit for three across). I'm likely to want to make some more of these boards,
    so there was very little loss. The blue plastic does come out a little
    wrinkled but seems to go through a second time okay. I can see that your
    method will ultimately produce less waste, so I'll give it a go.

    Viewed up close, how clean would you say the edges of the tracks are? I felt
    mine looked a bit rough, although I did over-etch.

    Have you done any double-sided boards with it? If so, how do you handle
    registration of the layers?
     
  11. Melodolic

    Melodolic Guest

    I forgot about that - the similar product mentioned in another thread came
    with 'white' PnP sheet for doing that - didn't occur to me that the blue PnP
    black resist would do the same job! Having tried cleaning it off, the etch
    resist does seem pretty tough.

    I got a flat a surface after drilling by deburring using a spot cutter. That
    said, the holes might upset the application of the resist. (I'd drill after
    etch anyway...)

    I'm using EAGLE and, so far, the pads all seem to have kinda largish holes -
    will look for ones with smaller ones, though . The drill bit is attached to
    a small vertical milling machine. I move the board by hand, looking first
    from the front to adjust the X position, and then from the side to adjust Y.
    That first board had no issues with hole alignment (not perfect, but the
    8-pin DIL skt went in okay).
     
  12. joseph

    joseph Guest

    They are not perfect but are fine for .01" traces, there is little room for
    error though. Use fresh, warm etchant and agitate like mad to get it done
    quick.

    Yes on the double sided. I put an extra via at each corner as registration
    marks. Iron one side and drill the registration marks. You have to remove
    any hole "fuzz" from the drilling. Then hold the PCB to a bright light and
    "try" to line up the PnP for the other side. This was ok but not to good.
    I've had better luck by drawing a line around the perimeter of the board,
    make sure it prints out. Then align this perimeter line with a corner* of
    the PCB. Iron one side, flip, align the other side with the same corner,
    iron. *If the edges of your raw PCB are not "sharp" it will not be easy to
    get good alignment. If so, cut then first to get a good edge.

    A cheap ($50, plastic housing) table-top diamond blade wet tile saw from
    home depot (or was it Lowes?) works great.

    jj
     
  13. Melodolic

    Melodolic Guest

    Do you use a tray or a tank?


    This is roughly what I've been thinking of trying, except I was considering
    drilling a couple of thin pilot holes and pushing pins through the top layer
    PnP and then the board. If a pair of diagonally-opposed corners are pinned,
    about half of the area is still accessible to the iron, so it should be
    possible to get enough adhesion before removing the pins to finish.

    That could be a better option. As a matter of interest, how do you do vias?
    Didn't there used to be some sort of little hollow, stubby 'pins' specific
    to the purpose?

    Interesting, but I'm getting short on space. :) I should be able to skim
    the edges square in the milling machine, however.
     
  14. JeffM

    JeffM Guest

    Have you done any double-sided boards with it?
    :I put an extra via at each corner as registration marks.
    :Iron one side and drill the registration marks.
    : jj ( joseph)
    :
    I agree up to that point.
    I used stick pins thru the holes to line up side 2 of the blue stuff.
    Start ironing where the pins aren't
    and after enough of the toner has adhered,
    pull the pins out and finish ironing.
    ..
    ..
    BTW, Walter Harley's layout/etching philosophy
    is closer to mine than is yours:
    http://groups.google.com/group/sci....rd+the-more-copper-you-can-leave-on-the-board
    news:[email protected]
     
  15. Jamie

    Jamie Guest

    photo injet paper with the image on the glossy
    side works wonders, just detach with water.
    also, i have seen the glossy pages from mags be used
     
  16. joseph

    joseph Guest

    Just been using a tray.

    Sounds like the pin method of alignment should work. Once you get it
    aligned you should be able to remove the pins. A little finger pressure is
    usually enough to keep the PnP from sliding around on the PCB. I always use
    a blank sheet of paper between the iron and the PnP to help the iron slide
    better.

    Run a wire through a hole and solder both sides for a via. Just make sure
    you don't place a via under a SMD chip!
     
  17. JeffM

    JeffM Guest

    I always use a blank sheet of paper between the iron and the PnP
    Pseudo-PTHs is the part that makes DIY a pain.
    Yup. Learning to use the *keepout* command early on
    will make life much easier.
    ..
    ..
    Joseph,
    It would be nice if you would fiollow the convention in these groups:
    Trim and bottom-post.
     
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