PCB etching with ground plane

Discussion in 'The Projects Forum' started by blah2222, Mar 21, 2014.

  1. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
    554
    33
    Hi all,

    Quick question regarding etching a pcb with a ground plane, using the toner transfer method.

    Are my only options either to cover the ground plane with toner (wasteful) so that the etchant doesn't eat up that copper or to cover the ground plane with a Sharpie marker?

    Wondering what people have done for this.

    Thanks!
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,361
    Spray urathane lacquer over the ground plane.
     
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    R!f@@, SgtWookie and ronv like this.
  4. bertz

    Member

    Nov 11, 2013
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    31
    Try the photo resist method, you'll never go back to toner transfer. I built an exposure box using UV LEDs. Takes 2 minutes for exposure, 30 seconds to develop and 10 to 15 minutes to etch.
     
    GopherT likes this.
  5. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
    554
    33
    Thank you for the suggestions.

    Timing is somewhat critical and I just wanted to do some quick prototyping, otherwise I'd use a professional service for sure and I don't quite have the resources for UV/photoresist.

    Might have to just to go with marker or lacquer.
     
  6. sirch2

    Well-Known Member

    Jan 21, 2013
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    betz - I gave up with photo resist and went to toner transfer when the method became fairly well established. I always found it hard to get the exposure time right and get an even exposure with photo resist. With toner transfer there is only the echant needed reducing the number of chemicals, processes, etc.
     
  7. alfacliff

    Well-Known Member

    Dec 13, 2013
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    masking tape on the back side works too, and is easy to clean off.
     
  8. bertz

    Member

    Nov 11, 2013
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    My experience has been quite the opposite. I used the toner transfer method for years and the results were adequate at best. I still use toner transfer for my silkscreens but the photo resist method allows much finer traces. Exposure time is a non-issue. 2 minutes in the exposure box - that's it! I was successful with my very first attempt.

    The cost of pre-sensitized boards discouraged me from using this method for a long time. But the availability of low cost boards on e-Bay makes this a no brainer.
     
    GopherT likes this.
  9. snav

    Active Member

    Aug 1, 2011
    100
    10
    I would like to try screens but have met with a dearth of info for small scale/prototype size equipment. Anyone have recommendations?
     
  10. #12

    Expert

    Nov 30, 2010
    16,283
    6,795
    I did some photo sensitive boards. I used the sun for the UV light, but I live in Florida, not Pennsylvania. The difficult part for me was getting the circuit on a clear sheet, so I had my friend make it because he is a printer. I guess you could do that with a laser printer now. I sent him a huge drawing of a round circuit board on an 8&1/2 by 11 inch piece of paper and he reduced the drawing to 1/4 inch diameter circles and sent me a clear sheet with several hundred copies of the board on it.

    It turned out really well because the huge black areas were very dark after they were shrunk down to about 1/32 of the drawing size.
     
  11. bertz

    Member

    Nov 11, 2013
    238
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    I built an exposure box. The box was built from ½” poplar sides and ¼” poplar top and bottom. Inside dimensions of the box are 4.8” x 7.25” x 3” deep. I used 96 UV LEDs arranged in a 12 x 8 matrix mounted on a printed circuit board. The printed circuit board mounts into the floor of the box on ¼” standoffs.
    The LEDs had a luminous intensity of 1200 mcd and a viewing angle of 160 degrees. The broad viewing angle was important because it projected a nice even light at an exposure distance of around 3”. The LEDs were wired in a series-parallel arrangement with 3 LEDs in series with a 100 ohm current limiting resistor.
    http://www.ebay.com/itm/231040487215?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

    A 3/16 acrylic plastic window was fitted into the top of the box for exposing the artwork. My projects are not very big and this little exposure box will nicely accommodate a 4” x 6” board. I was warned about using regular window glass as it attenuates UV wavelength light.
    I mounted a small aluminum enclosure on the side of the box for mounting the ON-OFF switch and a jack to plug in the 12 VDC power supply.
    I found a source of inexpensive pre-sensitized boards on e-bay which makes this whole venture worthwhile.
    http://www.ebay.com/itm/400569497455?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

    Step 2:
    I made a test strip wherein I exposed a 1” x 6” strip in one inch increments of 30 seconds for each increment. This meant that the first increment was exposed for 3 minutes and the last increment was exposed for only 30 seconds. After developing the strip in a NaOH solution (10 g/liter), only the last 30 second patch was under exposed. This means that anything over I minute will be sufficient exposure. Developing time was about 30 seconds and this is temperature dependent.
    Step 3:
    Next I exposed a pre-sensitized board with the artwork for a circuit I had developed. The artwork was printed on regular transparency using a laser printer. The artwork was doubled up because when I held a single transparency up to the light it appeared to be too porous. I exposed the transparency for 2 ½ minutes. The end result was an almost perfect exposure except that some of the UV leaked through the blanked off areas. In the future, exposure will be limited to 2 minutes or less.
    Step 4:
    Etching the boards using Ferric Chloride. I stumbled on a method where I float the boards on top of the solution. Total etching time is 15 to 20 minute depending on age of the solution and temperature. I still use the toner transfer method for silkscreen, but I am thoroughly delighted with the photo resist method for the traces.
     
  12. Robin Mitchell

    Well-Known Member

    Oct 25, 2009
    732
    200
    Try to save toner? Dont be tight :p. If you use only toner then you can get some really nice quality boards. Using a marker will result in copper pours that look like they have been scribbled in. Do the flavour a favour and use all toner ;)
     
  13. DickCappels

    Moderator

    Aug 21, 2008
    2,651
    632
    Similar to Mr.Chips's suggestion, I paint ground plane with cheap clear fingernail polish -it holds up much better during etching than the ink from a sharpie, and you can remove it pretty easily if you want with acetone and a scouring pad or sand paper.
     
  14. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
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    Do they ship free. ?:D
     
  15. sirch2

    Well-Known Member

    Jan 21, 2013
    1,008
    351
    I used them and it was about $20 all-in for 10No. 10cm x 5cm boards and they turned it round in about 10 days from order to delivery to the UK. Great service.

    However they only do batches of 10 on smaller sizes (so could be a lot of waste even if it is fairly cheap) and 10 days is a bit of a delay if you are prototyping.
     
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