To tin or not to tin that is the question

Discussion in 'General Electronics Chat' started by spinnaker, Oct 30, 2010.

  1. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
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    What are the latest thoughts on tinning PCBs?

    I have read it should be done and I have read a lacquer coating will work just fine.

    I have also read that it is pretty much mandatory for surface mount but I will not be doing any surface mount any time soon.

    So what are the thoughts?

    If yes to tinning, can tinning chemicals be purchased in craft shops?
     
  2. jpanhalt

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    Jan 18, 2008
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    I used to tin (dip conversion coating) routinely. Then tried non-tinning. It works just great without tinning and a final conformal coating prevents corrosion. Some hints:

    1) I use photoresist. I leave the photoresist on the board until I am ready to solder it.
    2) I will sometimes spread a very thing layer of paste flux on the board after removing the photoresist. It seems to work better than tinning as an aid to soldering.
    3) If you look at some of my projects in the Completed Projects forum, you will see the results. I will never return to dip tin. Now, will I consider solder plating? Yes, but that is way in the future, if ever. I will be using a board house before that.

    John
     
  3. spinnaker

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    I have also heard about using paste flux for corrosion protection.

    When you "final conformal coating". Is this the special conformal coating from PCB manufacturers? Or will some other common coating work?
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    I've used a tin plating solution for 40 years with no problems and consistently good results.
     
  5. jpanhalt

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    So far as I know, "conformal coating" is just an acrylic lacquer. I do happen to use the product from MG Chemical. I like the smell. You can also find coatings in various colors, if that appeals to you. Be sure to remove flux before coating. I use an alcohol (ethanol)-acetone dip (2 or 3 :1), because I have gallons of absolute alcohol available. Denatured alcohol will also work. There are many different formulations of denatured alcohol; not all are safe for the cheaper styrene plastics. So, use some judgement in how you use them. An old toothbrush is perfect for cleaning and testing. If your cleaning solution melts the toothbrush, it may also affect some of the plastic components on the board.

    John
     
  6. DonQ

    Active Member

    May 6, 2009
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    For homebuilt boards, tinning makes soldering so much easier, especially if it is going to be anything more than a couple of days till you are going to be soldering. Once the copper starts to discolor even a little bit, it starts to resist the solder so it takes lots of flux, or an aggressive flux, and maybe some more heat.

    The other side of the coin is that the mix for tinning at home is noxious. It doesn't smell bad, but it is really bad for you. Since it doesn't smell bad, you might be more likely to not be careful about getting it on you. Bad idea to be sloppy wit handling this stuff!

    At board houses, there are a wide variety of different coatings available for different purposes, and at different prices.

    As for 'conformal coating'... all that really means is a coating that conforms..., to the shape of the parts you put it on. This includes a wide array of options. One extreme case that I used was much like an epoxy coating, that you put on about 1/8 inch thick, and completely enveloped the components (I think it may have been an MG product). This protected from the elements, and the 185g acceleration forces that this circuit was expected to experience, but made reworking any circuit problems a real disaster.
     
  7. thatoneguy

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    Some people I've seen use Testor's "Transparent Candy Emerald Green", Color #1601 for a "solder mask look" before adding components.

    It is a bit of a PITA to Toner Transfer the pads on an etched board for this, and removing them once the paint cures also is a PITA. I guess hot enough solder will melt it eventually, so the pad will take solder, but it doesn't look as nice as a clean tin bath.

    I have used it when repairing circuit boards where large traces have "blown" from too much current. I patch it with the 3M 1181 Copper Tape, then mask off most of the board, and hit it with the Testors transparent green. It usually doesn't match exactly. It does look quite a bit better than a black/charred PCB with shiny new copper on it, while the rest of the board has a green solder mask.
     
  8. jpanhalt

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    Jan 18, 2008
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    As a side note, some acrylic coatings/conformal coatings can be soldered through. Acrylics, by and large, are not particularly heat stable. Cyanoacrylic adhesives can be used as temporary fixturing agents for SMD parts. Soldering heat will make them evaporate.

    John
     
  9. DonQ

    Active Member

    May 6, 2009
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    And that smoke smells so good too! Be sure to get some of it in your eyes. You haven't lived till you experience that.

    That's my off-the-wall way of saying "be careful with all of these fumes" (or else you may end up like me). Dust masks, even good ones, are completely useless for this stuff. Exhaust fans, open areas, etc, get it completely out of your house.
     
  10. thatoneguy

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    I spent 2 hours in the ER with an eyecup/flush about 15 years ago from using the "Thin/extra fast" CA. Had a small clog in the tip I didn't notice, went to apply it, squeezed, and Superglue splashed back to my face/eyes/shirt/etc.

    Remember to use safety glasses! Also be sure to have something to move the fumes away from your personal air intakes.
     
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