See through rectanges / large traces on Express PCB?

Discussion in 'General Electronics Chat' started by spinnaker, Oct 25, 2010.

  1. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
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    I have only done a few PCBs so far using the toner transfer method and Ferric Chloride as an etchant.

    I have noticed that on large (thick) traces and large rectangles, I get a bit of speckling on the copper. It almost looks like the copper started to etch there.

    I just printed out another project and noticed I can see through the toner to the printing on the page.

    Should I be able to see through the toner? Is this the reason I am am seeing this problem?

    Or is it another reason? Perhaps leaving the board in the etching solution too long?
     
  2. radiohead

    Active Member

    May 28, 2009
    474
    31
    First, what are you printing on? Are you using printed circuit board transfer film (the blue stuff) available from All Electronics Corp., glossy photo paper, or a magazine page? Circuit board transfer film is the best. I haven't tried the other methods, but I've seen it done.

    Use a swiss file or similar to file down any ridges or burrs on the edges of the card after you cut it to size. Failure to do this will prevent heat transfer from the iron to the clad board.

    Next, be sure to thoroughly clean the copper clad with a (black) 3M abrasive pad. Grade #0 fine steel wool will work, but ensure ALL of the woollen fibers are gone, and the copper has a nice, bright sheen before you iron on the transfer. You can also use an SOS pad or equivalent; you must make extra sure ALL of the soap residue is completely gone from the copper clad and the copper is dry before you iron.

    Assuming you cleaned the copper clad so all the oxidation is gone from the copper, align the transfer film onto the copper and apply your iron (approx 125 degrees F) with moderate to heavy pressure to start melting the toner to the copper board. After a minute or so, lighten the pressure and move the iron around to make sure the copper board gets nice and hot. This transfer usually takes about 5-6 minutes of ironing or so. Don't neglect to pay attention to the edges of the board, as the edges will be the first to cool down and leave you with possible broken or non-transferred traces.

    After you have ironed your board to your satisfaction, let it cool down for about 10 minutes or so. After that, hold it under cold running water for about 2 or 3 minutes to stop the cooking process. Pat the board dry with a paper towel or two.

    Once the board is cool, gently peel off the transfer film. If any traces failed to stick to the copper, don't worry. Obtain a Sharpie marker (felt thickness us up to you) and use it to dab in the lines that are missing or broken. Inspect all the transfer lines to ensure there are no thin spots. If there are, or if you suspect there are, dab the spot with the sharpie.

    Before you etch, the sharpie ink must be completely dry. You can put it in a 200 degree oven for a couple minutes to speed the drying process. DO NOT IRON sharpie trace lines.

    Of course, you are keeping your ferric chloride in a plastic container like an old juice bottle or similar. Heat a pot of water on the stove to just below boiling and dump it in a stoppered sink. Add some hot tap water to bring the temperature down a little if you like. Float the bottle of ferric chloride in the hot water until the solution is warm. Ferric chloride works better and faster when it is around 100 degrees F. If the bottle begins to expand, just loosen the cap to release the pressure, then tighten it back up. After you take the bottle out, put some dish soap in the water and run hot tap water to get a little suds.

    Gently pour the ferric chloride into your plastic tray and add your board. There is no need to "help" the process with a sponge. Just agitate the liquid around a little, avoiding splashes. Once all the copper is gone that you want gone, use plastic tweezers (or if you're wearing rubber gloves" put the board in the soapy water and clean all the ferric chloride off. While you have the board in the water, you can use the scrubby, steel wool or SOS to remove the toner.

    Once the board is dry, and the traces are nice and shiny, coat the traces with a thin film of soldering flux. This will help reduce oxidation. Some people like to tin the pads and traces before drilling. The soft solder can help center the drill bit.

    I hope this addressed your concern. Sorry for the wordiness.
     
    Last edited: Nov 1, 2010
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