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Oxidised components

Discussion in 'Electronic Basics' started by David, Feb 18, 2006.

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  1. David

    David Guest

    I've been having problems with an SMD board that I've been making some
    modifications to. I suspect that I've damaged the component (I'm no expert
    on SMD and can only say that the part is either a resistor or capacitor) in
    that I can't see any metal on one end and it's extremely difficult to get
    any solder to stick to it. Would excessive heat and/or flux oxidise the
    metal in such a short space of time? If so, how can I fix it?
     
  2. Chris

    Chris Guest

    Hi, David. Sorry to be the bearer of bad news, but the solder has
    actually leached away the termination on the one side where you can't
    see any metal. There's no way to make a connection, even if you
    haven't killed the part with the iron by overheating. It will never
    make contact.

    You'll have to buy a new part, I'm afraid.

    While you're at the store, try to pick up some eutectic silver-bearing
    solder (Sn/Pb/Ag 62/36/2%, .020" dia.) with a good flux. This mixture
    assures minimum melting temperature, and the silver will help to reduce
    the leaching effect. The self-cleaning fluxes are too mild, and don't
    do a good job of wetting.

    Also, get a temperature-controlled soldering iron, with a suitable tip.
    Keep the tip at 750 or so, to avoid overheating of the part.

    Solder-Wick or other copper despldering braid is also a good thing to
    have while reworking. Try to get the narrowest possible braid (.062"
    is good).

    Do these things, and with good soldering technique, you won't have to
    worry about this again.

    Good luck
    Chris
     
  3. David

    David Guest

    Dammit dammit dammit. That's my PS2 up in smoke :(

    Actually the mod is working to some extent. When it decides to boot it works
    for up to 30 seconds before freezing. It works sometimes when I disconnect
    the power and then reconnect. It also works sometimes if I tap the unit.
    This suggests that all the connections work, but that one or more are a bit
    flaky. I suspect this part I've been having problems with.
    I've been using a temperature controlled iron. Always a bit wary of
    overheating components so kept it at no more than 300 C (572 F). The solder
    I have melts immediately at this temp but I have had it as low as 280, which
    means the solder doesn't melt properly unless the iron's been touching it
    for a couple of seconds.
    Thanks for the tips. :)
     
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