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Desoldering question

Discussion in 'Misc Electronics' started by Mr. INTJ, Aug 29, 2008.

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  1. Mr. INTJ

    Mr. INTJ Guest

    I started doing hobby electronics again fairly recently, and recycling/
    scavenging is a big draw for me. As it happens, my company throws away
    lots of useful stuff, and over the past year I've brought home lots of
    circuit boards with various useful parts on them.

    I've got a solder sucker and solder wick/braid, but components with
    more than two or three leads continue to be a problem for me. I have a
    little soldering station with a soldering iron, but I've been thinking
    that I probably need some hot tweezers or a heat gun of some kind.
    Most of the stuff that I'm recovering from these boards are through-
    hole components ... I haven't graduated to SMT-at-home just yet.

    I don't mind springing for the right tools, but I don't want to buy
    something only to find that it still isn't very effective.

    I'd like to hear from the folks that do a significant amount of this
    kind of thing (desoldering), and which tools/methods they favor.

    Thanks!

    Mr. INTJ
    San Diego, CA
     
  2. Eeyore

    Eeyore Guest

    Well there's no substitute for a de-solder tool (manual or vacuum). If you
    have a Weller TCP, I think there's an accesory for it. There's still a
    knack to it though.

    Graham
     
  3. Guest

    Use the solder wick on multipin items just wick the bottom of the
    board and then wiggle the pins to be sure that they are loose. When
    you are using surface mount multipin items use the solder wick on top
    of the pins and then touch each one with the iron tip and lift the pin
    off the surface with a small tool. You must be careful not to over
    heat the pin... you know where it goes and the over heating of the
    connector wires from the pin to the chip element is a very bad
    thing.
     
  4. While you are completely right, it is normally not very critical. When
    the board was assembled, the entire component was probably immersed in
    molten solder for a couple of seconds.
     
  5. Jasen Betts

    Jasen Betts Guest

    it's a lot of work for little gain. but it's a game I've played too.
    those tools aren't really suited to scavenging, more to repair.
    get a propane blow torch, a box, and some safety glasses

    heat a section of the board until the solder is liquid an then bang it
    on the edge of the box, repeat until the solder/components come of.

    the trick is to heat rapidly so the heat doesn't have time to damage
    the components.

    I find with the the fibreglass boards with plate-thru holes you need
    to heat until the layers just start to separate. (you hear a popping
    sound)

    the boards will be destroyed in this process but you're after the
    parts right?

    probably best to do this outside, or in the garage: all sorts of evil
    smelling fumes come out of the overheated fibreglass resin, and solder
    droplets stick to synthetic carpet real well.


    another way is to cut the board up with a hacksaw or side cutters
    and then extract the pins one at a time

    Bye.
    Jasen
     
  6. Rich Webb

    Rich Webb Guest

    If only the components are important, and not the board itself, then a
    propane torch with a fan head can work. Wave the flame over the back
    until the solder liquefies, whack the board on the workbench, then chase
    after all the parts that just popped out. Beware of flying molten
    solder. Whacking the board inside a (non-flammable) box helps to keep
    the parts and the solder drops corralled, of course.

    If both the components and the board are important (or you want to
    practice for when they may be), you will find that, after you've wicked
    or sucked all easily accessible solder from a multi-pin object, it's
    still held fast to the board by the multiple tiny solder points. What
    can be helpful is to briefly reheat each pin with a clean iron and then
    nudge the pin with a dental probe or knife blade towards the center of
    the hole as the iron is removed and the solder cools. Often a brief
    touch with the iron is all that's needed and you can go down a row of
    pins very quickly,

    As regards SMT, it's really not that difficult (often easier than
    through hole); it just looks intimidating, at first. There are several
    tutorials on the web. A good place to start is the tutorial section over
    at http://www.sparkfun.com/commerce/categories.php
     
  7. GregS

    GregS Guest


    I have all the tools to do this, but since I hardly use it the Weller sucker
    it gets all messed up leaving it on. Its a major effort to reclean the tip.
    Regardless, the recommended method of removal is to cut all
    the pins first, and removing many components with intact leads is a chore.
    I can't live without solder wick, fresh, or freshly refluxed. Get a liquid flux pen
    and apply to pins regardless of tool.

    greg
     
  8. Gerard Bok

    Gerard Bok Guest

    A PACE pedair :)
    And at least one spare handle because the unit sucks much faster
    than the solder can cool down. I don't mind a coffee break but I
    hate it when I need to take a break, just because the desoldering
    device got too hot to handle.

    I guess the beast has been replaced by
    http://www.happcontrols.com/tools/92157100.htm
    (And I doubt if you like its pricetag :)
     
  9. Eeyore

    Eeyore Guest

    If the device is dead )or low cost) you simply cut every pin and them remove
    the debris pin by pin. The PCB is 10000 x more valuable than a dead bug.

    Graham
     
  10. Eeyore

    Eeyore Guest

    Try desoldering it in a couple of seconds and see how many tracks lift,
    PTHs break etc etc.

    Graham
     
  11. Eeyore

    Eeyore Guest

    Useful to whom ? If you're just hoarding forget it. I generally won't ever
    use recycled semiconductors anyway. Too risky.

    Graham
     
  12. Guest

    Wave solder is stamdard. boards are pre-heated and then go surfing...
    so to speak. But a percentage don't come through it alive... they
    must be re-animated. To borrow one from the Cthulster. Any way its
    best to be careful. Also with your primary tool... fingers.
     
  13. John Nagle

    John Nagle Guest

    Yes. And the temperature and time of the solder wave or hot-air
    reflow was controlled to stay within the limits of the parts.

    John Nagle
     
  14. Wim Ton

    Wim Ton Guest

    I started doing hobby electronics again fairly recently, and recycling/
    I used a propane torch, till I found out the an electric paintstripper give
    a more controllable heat. Watch out for all the SMD resistors and
    transistors blown around ;-) I still have to remove heavy leaded component
    from multilayer boards with a biggish (60 Watt) soldering iron.

    Wim
     
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