De-soldering tips?

Discussion in 'DIY Discussion' started by mjp200581, May 16, 2012.

  1. mjp200581

    mjp200581

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    Does anyone have any helpful hints, tips or advice on how best to go about de-soldering components with multiple legs from a circuit board?
    I need to replace a relay on my CDP but I know from past experience that I haven't quite got the hang of de-soldering such components.
    I have a spring loaded de-soldering suction pump which I find great for clearing the whole in the board once the component is already out and I have some solder-wick which sort of works to wipe away solder but doesn't exactly wick it away.
    Suggestions on a postcard please.
     
    mjp200581, May 16, 2012
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  2. mjp200581

    pete693

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    De soldering

    Assuming your desolder pump is clean and sucking well it should do the job.Before you start take the pump apart,very easy as the barrel will unscrew to reveal the innards.Remove the plunger and clean off any solder thats stuck to it.Make sure that the hole that the solder is drawn up through is clear.If there is a rod that is attached to the end of the plunger that passes through the hole in the spout make sure this rod has no solder stuck to it.
    The most important thing before starting to remove the old solder from the device you are removing is to apply fresh solder to each joint you are removing.The fresh flux from the new solder will mix with the old solder and allow it to flow more freely into the solder pump.If all the solder doesn't come out then apply fresh solder to the joint and repeat the process.
    Pete.
     
    pete693, May 17, 2012
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  3. mjp200581

    mjp200581

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    Thanks Pete, that's good advice.
    I never would have thought to add more solder first as it seems so counter-intuitive but what you said about the flux helping the solder to flow better makes perfect sense.

    I think part of my problem is that my solder pump has a very broad/blunt tip which is difficult to get close to the pool of solder. I'll try to make a narrower tip for it.
     
    mjp200581, May 17, 2012
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  4. mjp200581

    felix part-time Horta

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    Then you need desolder braid; Maplin sell it on the high street.

    Also buy a flux pen if it's in stock.

    You put the braid across the IC feet/other component, heat thoroughly with your solder iron on the top of the sandwich - and the braid should wick the remaining free solder away like magic. Your big iron is an advantage here - let is get to full temp, i.e. powered up at least 10mins before you use it - the energy stored in that wide tip does the work.

    About desolder braid:
    1) It is flux-coated so it encourages even old solder to flow well.
    2) A wipe with the flux pen over what you want remove also helps - stops old solder spreading like margarine then setting again across all the pins.
    3) Buy the narrowest braid stocked, it is woven copper so conduct heat really, really well and if its more than 2-3mm wide you'll need 25-40W iron to make it work at all. Wide braid will carry away heat so well the old solder doesn't even melt beneath it. With the narrow stuff you can actually pull it sideways through the sandwich, slowly, to pull off more solder as the braid saturates (which you will see - if changes form 'copper' to 'tinned' in appearance)
    4) Don't be afraid to use a really BIG soldering iron, short fast sufficient heating does much less damage than sitting there for 10mins with a 12watt weed that isn't up to the job.

    The final dirty trick for removing surface-mount ICs is simple: if you can, thread a thin wire under the body and capture both ends. Use the big iron and braid, and when the solder melts pull the wire out parallel with the PCB to lift all the legs at once, like a cheese wire. Sounds crude but it means you can re-use 64-pin Qpaks easily without hot air rework ;)
     
    Last edited by a moderator: May 18, 2012
    felix, May 18, 2012
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  5. mjp200581

    mjp200581

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    Thanks Felix.

    There are some great videos on youtube demonstrating the use of solder braid.

    There is a Maplin just 1/2 a mile from my house so I'll pop down tomorrow to pick up a flux pen and some braid.

    Thanks again, Mike
     
    mjp200581, May 21, 2012
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