Toner Transfer

Discussion in 'General Electronics Chat' started by sirch2, Mar 13, 2014.

  1. sirch2

    Thread Starter Well-Known Member

    Jan 21, 2013
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    I've been using laser printer toner transfer for a while now and it generally works well. However the latest board has some long thin tracks (for thermal reasons) on a sparsely populated area of the board. These tracks don't transfer well from paper to copper and I was wondering if anyone else has had this problem and if there are any fixes for it?

    By long, thin tracks I mean about 25mm x 0.25mm. I have done some very fine SMD stuff before without any problems but it seems much better on densely populated areas rather than areas with few tracks.
     
  2. shortbus

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    You can use a 'Sharpie' pen to fill in the missing toner after transfer.
     
  3. sirch2

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    Jan 21, 2013
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    Thanks, yes I've done that in the past but I find it hard to keep the tracks very narrow, perhaps I need a finer marker, if such a thing exists (currently using a Staedtler fine marker).
     
  4. spinnaker

    AAC Fanatic!

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    Make sure your copper is very clean. Scrub with one of those green scubbing pads.

    Try printing to wax paper.

    You should look into getting a laminator. Do your research because there are some brands / models that work better than others.
     
  5. sirch2

    Thread Starter Well-Known Member

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    I don't think the problem is board cleanliness, I do scrub and clean with acetone. Since it works on dense areas but not sparse ones I was wondering about just putting down some unconnected areas of copper.

    It seems curious that some tracks work and some don't.

    Here's the board BTW, it's the tracks on the right that cause a problem.
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Why do you have different trace sizes on your board.
    There is space enough for equal traces all around.

    I have inverted the image as blue on black is barely visible:

    [​IMG]

    I made also some handdrawn changes that made it possible not to go between IC legs:

    [​IMG]
    Bertus
     
    Last edited: Mar 13, 2014
  7. MrChips

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    Oct 2, 2009
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    If you are etching your own boards, try to leave as much copper on the board by using copper pour or floods. Not only will your etching solution last longer but also your board will take shorter time to etch.
     
  8. spinnaker

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    Acetone is not going to remove corrosion very well. You should really give those Scotch Brite pads a try. If you can find the ones that go into a drill press then even better.

    You might also not be applying heat evenly enough. Look into a laminator. It made a world of difference for me.
     
  9. sirch2

    Thread Starter Well-Known Member

    Jan 21, 2013
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    Thanks for all the replies.

    Bertus, thanks for the diagram, nice to not have the track between the IC legs. The two devices out on their own on the right of the board are thermistors, one is self heating and I want as small tracks as possible to reduce heat conduction through the tracks.

    Mr Chips, I have found with toner transfer that big areas of copper look really rough so I generally avoid them but as I said in #5 I may well use that approach here. Generally I dispose of the etchant after one use anyway.

    Spinnaker, perhaps I wasn't clear, I clean the board abrasively (I find 800 grit wet and dry gives a much better finish than scotchbrite) and then as a final degraasing step wipe over with acetone. I have produced many boards this way and it usually works well. Perhaps a laminator would help but the cost puts me off, what sort do you use? Have you modified yours to reduce the speed?
     
    Last edited: Mar 14, 2014
  10. sirch2

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    After a huge amount or googling and plowing through a load of pages on the subject I just thought I'd post my fixes for this issue in case anyone comes across it in future.

    First surprise was that I had the iron too hot, I tried it cooler and it worked better (wool/silk setting on my iron). Also I think the long thin tracks were failing because there was very little toner to stick the paper to the board so either the paper was lifting during the ironing process or the tracks were coming off in the soaking.

    So I added some copper pours (as I thought in post #5 and Mr Chips suggested). However a tip I came across to prevent pits in large areas of copper is to re-heat the board on the iron after the paper has been removed to re-flow the toner. This seems to work well.
     
  11. spinnaker

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    Sounds like a good idea on the sandpaper. I might even give it a try.

    I use the GBC H212. Mods where minimal. Got a pretty good price on eBay. They have some sort of plastic guides up under the rollers. Those guides will jam the board. I removed them. The sealer gets hot enough but you need to run it through 6 or 7 times to be sure. No need to mod the heater.

    I also have had success with my stove. I have one of those flat top electric stoves. I turn the stove on low and sandwich the board with it's transfer between paper towels an roll with a rolling pin. I have a post on that somewhere.

    I was thinking your other issue might be toner. Most folks only have good results with genuine HP cartridges.
     
  12. spinnaker

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    I really like the tip of heating the board again after paper removal. Can you explain how you do this exactly without lifting the existing toner?

    And how did you fix the problem of the toner coming off on the paper?
     
  13. #12

    Expert

    Nov 30, 2010
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    I think you're chasing a non-problem with the heat considerations for the thermistors, but, if it's a real problem, the pads are probably the worst factor. Thermistors come with very fine wire so I suggest you mount them using an inch or so of their own legs to isolate them thermally.
     
  14. sirch2

    Thread Starter Well-Known Member

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    Spinnaker - I just held the iron upside down (hot side up) and placed the board on it face up and let it heat up for a few minutes until the toner was soft. I think reducing the heat and adding the copper pours fixed the problem with the toner sticking to the paper rather than the board. I guess this is because the copper pours hold the paper down to the board better than thin tracks.

    #12 - the thermistors are in 0603 SMD packages. One of them is being used to detect drafts, it self heats and the draft takes away some of the heat, cooling it. Small tracks/pads and a small package make it much more responsive due to low thermal mass (and apologies if you looked at the PCB layout and saw the big pads - I posted an incorrect version of the board).
     
  15. spinnaker

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    That is what I sort of figured. It might make larger boards more difficult but doable.

    Interesting concept.
     
  16. Wendy

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    Mar 24, 2008
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    I'm currently working on some experiments where I hope to retire my laminator. I have qty 2 1/4" sheets of aluminum (8.25" X 8.25") that I will drill a thermocouple hole 1" into the side on one and see if I can use weights magazines and weights to do the thermal transfer. If it works I'll have to come up with an individual profile using a timer and temperature.

    I'll post it in the Completed Projects Forum if it works, where it will compliment this thread...

    How I make PCBs
     
  17. #12

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    Just another through hole guy in a surface mount world.:(
     
  18. spinnaker

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    Oh man that is almost signature worthy. :)
     
  19. #12

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    Somebody already used it.
     
  20. THE_RB

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    Feb 11, 2008
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    The problem with trying to do the whole PCB in one operation is the thermal expansion of the PCB. That causes movement of the artwork relative to the PCB at the edges, so the middle of the PCB can have fine detail tracks but at the edges it has expanded away from the middle and the tracks will smudge.

    Also, as the entire thing is hot it can move (nothing is stuck together, only held together), so the thermal expansion causes the PCB and artwork to move relative to each other.

    Using a laminator is much better because only a thin strip is heated at any instant so the rest of the PCB and artwork is cooler and "stuck together" and will not move, and the thin strip that is heated won't cause any larger thermal expansion of the whole PCB.

    When I changed from pressing and heating the entire PCB to using a laminator I was able to eliminate smudging, get much finer tracks, and had no more issues with the PCB and artwork moving relative to each other.

    In my opinion you're going in the wrong direction. The ultimate toner transfer device would be a laminator with adjustable speed and temperature, and maybe multiple heated rollers so you could do less passes. :)
     
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