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Cleaning copper connections for high precision instruments

  1. Sep 20, 2015 #1
    Hi all,
    Here's my first post with a question I've been trying to solve for a while.

    I work with electronic components of very high quality and we try to make all our connections using thin copper ribbons of various thickness. I have started cleaning my copper connections with a solution of vinegar and salt (more or less 3g of salt in 200ml vinegar). I believe that combination yields sodium acetate and hydrogen chloride. It gets rid of any oxidation on the copper. Even copper that looks very clean appears much brighter and cleaner when the solution is applied.

    My problem is what happens after the procedure: the piece of copper after a while becomes much more oxidized than before (the new oxidation starts to become visible after a few hours). I have started to clean the copper with isop. alcohol, which sometimes works well, and sometimes doesn't. I suspect the piece must be scrupulously cleaned in order not to oxidize again (in the rate described), which is sometimes very difficult. (Let me add that this is a problem because often I must clean the parts a couple of days before soldering them, and in other cases the connection is merely mechanical).

    My question is whether any good soul here would know how to "neutralize" the sodium acetate/ hydrogen chloride solution right after it has cleaned the copper. The reason why the copper oxidizes really fast if I don't clean the solution with alcohol and why it doesn't when I do is beyond me. At any rate, I am looking for a more practical way to maintain the copper bright and clean after using the vinegar solution, for as I said cleaning it with alcohol is very time consuming in order to be effective.

    Thanks in advance for any help.

    Marcel
     
  2. jcsd
  3. Sep 20, 2015 #2

    berkeman

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    Welcome to the PF, Marcel.

    Can you post some pictures of the connections you are making?

    The standard for good electrical connections came from Bell Labs (in my experience) -- make multiple connections with sharp pointed contacts, and make them gas-tight (which eliminates oxidation). Is there any way you can use that paradigm to improve your electrical contacts?
     
  4. Sep 21, 2015 #3
    Hi there,
    I'm sorry, but that was not what I asked. I guess my main question is why the copper piece needs to be rinsed after the vinegar solution is applied? Why the solution produces the fast oxidation if it's not rinsed off after it cleaned the copper piece?
     
  5. Sep 21, 2015 #4

    Nidum

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    Verdigris
     
  6. Sep 21, 2015 #5
    Again... why is it formed if the vinegar solution is not rinsed off?
     
  7. Sep 21, 2015 #6

    Nidum

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    The residual traces of vinegar and other chemicals will continue to attack the copper surface after all oxide has been removed .

    Vinegar and salt could potentially form several different compounds with copper but most problematic one for you is likely to be copper acetate . In thin film form not easily distinguishable from copper oxide .

    To prevent this continuing attack on your copper surfaces scrupulous removal of residues is essential . Alcohol is probably not best cleaner . There are specially formulated cleaning and passivating agents available for this purpose .
     
  8. Sep 21, 2015 #7

    Nidum

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    Citric acid may be better than Vinegar/salt for your purpose of removing oxides from copper .

    Citric acid has a relatively gentle cleaning action and residues can be easily washed off with mild detergent solutions followed by plain water .
     
  9. Sep 21, 2015 #8

    Borek

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    It is not just the low pH that etches the oxides, from what I remember presence of chlorides plays a crucial role. Replacing vinegar with other acid won't change that.
     
  10. Sep 21, 2015 #9
    Thank you, that's helpful. I've tried lemon instead of vinegar, but it creates a similar if not the same problem. Washing in water is not an option, unfortunately. The cleaning needs to be done in place, on rather small connections. I generally do everything with qtips, which obviously is a very limited procedure as far as the capacity to completely remove the acid.
    Why is copper acetate more problematic than oxidation?
    What do you suggest instead of alcohol?
     
  11. Sep 21, 2015 #10

    Nidum

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  12. Sep 21, 2015 #11
    thanks.
    Why is copper acetate more problematic than oxidation?
     
  13. Sep 21, 2015 #12

    Nidum

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    They all work quite well and leave no visible residue .

    Brass and copper materials treated with these products do though seem to be protected from atmospheric corrosion for at least several hours after application so there must be some very thin protective film left on components .
     
  14. Sep 21, 2015 #13

    Nidum

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    What I meant was that your Vinegar/salt mix removes the copper oxide but can replace it with copper acetate . Really you want neither .

    Copper acetate is an unpleasant greasy substance that is difficult to clean off entirely once formed except by abrasive methods . Best therefore to entirely prevent it's formation by removing any Vinegar/salt residue on components completely and immediately after their use .
     
  15. Sep 21, 2015 #14
    Got it, thanks again. Question: if we leave the acetate layer there, would it be more corrosive than oxidation in the long run?
     
  16. Sep 21, 2015 #15

    Nidum

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    Copper oxide thin films are relatively benign and slow forming in ordinary atmospheric conditions .

    Copper acetate once first formed seems to remain active and continue to corrode into the parent metal for long periods .

    As you see in the Verdigris link the chemical substance that actually forms over long periods of time gets to be far more complex than simple Copper acetate and there can be several different formation and corrosion mechanisms at work .

    There is a similar problem with some acid flux residues after soldering . Unless scrupulously removed they seem to continue causing corrosion forever .
     
  17. Sep 21, 2015 #16
    very helpful, thank you.
     
  18. Sep 21, 2015 #17
    Someone else has just suggested something that might do the trick: instead of alcohol, use an alkaline solution (eg water with baking soda) to both neutralize the acid (acetic or citric) and finalize the cleaning. I would then simply dry the piece with a hair drying. What do you think?
     
  19. Sep 21, 2015 #18

    Nidum

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    Dilute aqueous solutions of baking soda and other chemicals like Sodium Hydroxide are often used for neutralising acid residues on manufactured items but always in conjunction with a final rinse with clean water .

    The final rinse is essential to avoid problem of leaving new residues on components which could be as harmful as the ones that have been removed .
     
  20. Sep 21, 2015 #19
    No doubt.
     
  21. Sep 23, 2015 #20
    I have tried the baking soda after the acid. I'm not sure it does what it supposes to do. When I clean with the vinegar/salt solution I can see on the white tissue I use the blue residual of the oxidation: the copper looks perfectly clean. Then when I apply the water/baking soda solution to neutralize the vinegar, the tissue shows a yellow residue and the copper acquires a slight shadow (not really uniform). If I clean again the same copper with vinegar it gets rid of the shadow and shines again...
     
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