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So what's the truth about lead-free solder ?

Discussion in 'Electronic Repair' started by Eeyore, Jul 24, 2007.

  1. N Cook

    N Cook Guest

    But those are RoHS compliant.

    More to the point, for removing laquer , not hard tin , from round surface.
    I just tried a Skarstan blade , singly, in its normal wooden handle and it
    scrapped the hard tin off some of the flat leads of the latest batch of
    TIP35C/36C power trannies that I bought. Down to the copper with no
    difficulty, I think I can ignore the tin-pest developinmg on the narrow
    edges as long as the main surface contact areas are functionally solderable.
     
  2. PeteS

    PeteS Guest

    This subject came back to bite me yet again today. There's a great part
    I wanted to use, but we'll have to refinish the pins first if I do, so
    I'll see if there's a different part I can use in this application. For
    the record, it's a high speed (not full speed) USB peripheral controller
    and the lead finish is 98/2 SnCu.
    I consulted with a few of the manufacturing people and one of the
    biggest problems with RoHS profiles is the solders aren't eutectic, so
    getting a proper bond is more difficult quite apart from the problem
    with tin whiskers.

    Cheers

    PeteS
     
  3. Chris Jones

    Chris Jones Guest

    Ok, it was just a thought. I was imagining the round pin of a T03 when I
    thought of that.
    Do you mean tin pest or whiskers? I would have thought that the edges would
    be the worst place for whiskers to sprout from.

    As for solderability, I would have thought that if the pins are exposed to a
    sufficient quantity of sufficiently hot SnPb solder for a sufficient time,
    then the tin would dissolve into the solder, like fine copper wire has an
    annoying tendency to do. If overheating of the semiconductor device is a
    risk, then perhaps it could be done in a couple of goes, allowing to cool
    in between. The resulting tin-rich solder could either be removed and
    replaced with fresh solder, or just diluted with more fresh solder.

    I'm sure there would be plenty of people interested if you find a good
    technique for small-scale use.

    Chris
     

  4. High temp mag wire... not the shitty for high temp uses "Nyleeze" does
    NOT burn off with the application of heat, and requires scraping to
    remove the insulation. Before Nyleeze, the requirement was the standard
    for decades.
     
  5. N Cook

    N Cook Guest

    With the sort of stuff I deal with, geometry-wise, tin whiskers have no
    relevance I would have thought.
    It is that film of tin , all lovely mirror shiney when new turning to grotty
    dusty grey (tin pest) , expanding in the process , and physically pushing
    the solder away from any conduction maybe only 2 years down the road.
    I am not sure just heating legs with solder would affect the integrity of
    that initial tin film without some sort of mechanical intrusion while hot
    and mixing.
     
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