Copper in solder?

Discussion in 'General Electronics Chat' started by BrainFog, Sep 6, 2011.

  1. BrainFog

    Thread Starter Member

    Jan 24, 2011
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    Hello

    I have spent so long searching for this using google it is daft but all I get is information about how solder binds to copper on PCBs

    Yesterday while looking for solder to buy, as I am almost out, I noticed solder that contained copper. Only a tiny amount , think it was 0.7% Copper and 99.3% Tin.

    How would having copper in the solder affect the solder's properties and how would it change my ability to use it as solder componants to PCB's?

    Thank you
     
  2. #12

    Expert

    Nov 30, 2010
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    Have you ever seen how fast solder eats a bare copper soldering tip?
    I wouldn't worry about copper in my solder. It's going to have copper in it a few milliseconds after it hits the circuit board, anyway. It's the 99% tin that I don't know about.
     
  3. BrainFog

    Thread Starter Member

    Jan 24, 2011
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    I am asking more out of curiosity, it must have copper in it for a reason and I want to know that reason.

    Why do you question the tin?
     
  4. JingleJoe

    Member

    Jul 23, 2011
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    Yes I have, I had a copper cored solder tip once, but it didn't have a copper core for long! I didn't notice this untill I turned the iron around one day and a huge blob of solder sort of fell out of nowhere, the tip was hollowed out!

    If anything, it improves conductivity and raises the melting point but in such small an amount I can't see it having much effect, it may just be impurities the manufacturer can't be bothered removing.
     
  5. steveb

    Senior Member

    Jul 3, 2008
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  6. steveb

    Senior Member

    Jul 3, 2008
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  7. #12

    Expert

    Nov 30, 2010
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    I question the tin because I've never used 99% tin. I don't question the copper because I've used solder with copper in it.
     
  8. BrainFog

    Thread Starter Member

    Jan 24, 2011
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    I mistakenly bought pure tin a while ago and I couldn't tell much of a difference apart from a duller finish.
     
  9. Papabravo

    Expert

    Feb 24, 2006
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    An alloy is a combination of two or more metals. Different proportions result in different properties. You learn these things in an engineering cours called properties of materials. The most common type of solder used to be made from a Pb-Sn (Lead-Tin) alloy. Among its properties was a low eutectic temperature. That is where the temperature is the same for the liquid to solid transition as for the solid to liquid transition.

    ROHS 2006 resulted in the abandonment of the Pb-Sn alloy for the less desirable alternatives. If I had to guess what the copper was for it might be the elimination of tin whiskers.
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    You really don't want to use pure tin, as voltage passing through it will cause "whiskers". Something about the crystalline structure of pure tin combined with current flow causes very thin structures to form, and was the cause of a failure of a Hughes Space & Communications satellite when a whisker shorted the power supply.

    The whiskers take awhile to form; can't remember what the particulars were. The addition of copper would likely prevent these whiskers from forming.

    I'm not very fond of very high tin content solder.
     
  11. SgtWookie

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    Jul 17, 2007
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    Last edited: Sep 6, 2011
    debe likes this.
  12. saturation

    Member

    Dec 21, 2008
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  13. Wendy

    Moderator

    Mar 24, 2008
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    Old solder (the good stuff) is 63% tin and 36% lead. Because lead is considered toxic it is increasingly being banned, which is a shame because it works extremely well.

    The new solder tends to be 95% tin and 5% silver. It has major problems, it grows whiskers (AKA dendrites), and has a higher melting point. It is a bit mechanically stronger, so it isn't all negative.

    In all cases the surface layer of copper alloys with the solder, which is why it bonds to the metal. It won't do that with aluminum, but there are pastes out there that will form an intermediate metallic layer that will get the job done. I don't know how good they are long term, when you mix several layers of metals bad things tend to happen due to electrolysis, but the old solder is pretty stable with copper, and I assume that is true of the new stuff.
     
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