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Removing relay without damaging pcb (plated through holes)

Discussion in 'Electronic Repair' started by [email protected], May 30, 2007.

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  1. Guest

    I have an old project where a relay is oddly stuck in a state with the
    common rail connected to the normally open contact. I can only assume
    that the two connections fused together during a high-current
    transient. The relay breaks a connection between an audio amplifier
    circuit and a subwoofer. I think my only choice is to replace the
    relay. There is however a problem where the pins of the relay are
    soldered to plated through-holes. This is making the relay nearly
    impossible to remove without risking damaging the pcb. Does anyone
    have any neat tricks to remove such a component safely?
    Thanks
     
  2. If using a desolder tool and solder braid still leaves it stuck it's often
    best to carefully wreck the component so you can treat each pin
    individually.
     
  3. N Cook

    N Cook Guest

    Make up a pyramidal truncated frustrum (Google) out of 4 pieces of tin-
    plate, wired together. Mask off that area around the relay, with the
    frustrum temporarily wired to the board. Mount board firmly in vice, near
    the relay. Pull and wriggle the relay when you apply heat from a hot-air gun
    directed into the frustrum.
    If you don't believe it will work try the technique with plated thru comps
    on a scrap board first. The hotter the air and quicker you are the better,
    if board starts to discolour there is probably some other mechanical
    restraint.
     
  4. Guest

    There is only one way: chop the relay up until you can get to each
    pin, and desolder those individually.

    I however would open the relay and file the contacts, far easier
    option.


    NT
     
  5. N Cook

    N Cook Guest

    As it happens, the last week I've been working on industrial boards with
    plated-through soldering. Thick board so only tips of IC leads protrude,
    very thin signal traces, traces to tiny pads on both sides of boards of same
    pin in some cases and plated vias under ICs as well. I know if i'd used
    "proper " vacuum assist desolder or butcher-and-remove single pins , many of
    those traces/pads would have dislodged.
    I had to sharpen the points of my large adapted circlip pliers to get the
    extra purchase on the ends of these 14,16, and 28 pin ICs. Not one dislodged
    track using a paint-strip hot-air gun. Next time i'll have to take some
    before and after pics for the doubting thomases.
     
  6. Smitty Two

    Smitty Two Guest

    I'm not one of the doubting Thomases. Hot air works well. So do the
    other methods, that you doubt. It's all about technique and finesse. The
    professional desoldering stations work extremely well when used and
    maintained properly, and virtually not at all otherwise. Blame the
    operator.
     
  7. CWatters

    CWatters Guest

    That's the way I'd do it.
     
  8. Meat Plow

    Meat Plow Guest

    That's the way I've done it.
     
  9. Marra

    Marra Guest

    I would just leave it as it is rather than knacker the board
     
  10. Guest

    Any recommendations on how to "chop up" the relay?
    Its a sealed plastic type.
     

  11. Are the pins smaller than the plated through holes. or are they a
    tight fit? If there is any free space you can remove the solder, then
    heat the pin till the solder melts and gently bend it loose from the
    wall of the plate through hole. I've done it that way for decades, but
    you should practice on a scrap board first.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  12. On Thu, 31 May 2007 18:48:04 -0700, the renowned
    Sharp cutters like these: http://www.wassco.com/shearcutters.html

    Cut into it from the top and keep cutting stuff away until just the
    pins are left. Be careful cutting away the plastic bottom that you
    don't scratch through traces or otherwise accidentally damage the
    board.

    If you have a *good* desoldering tool (with a vane pump etc.) it may
    be possible to suck almost all the solder out of the holes so they
    break away when wiggled without damaging the plated-through holes, but
    it's not always possible, and it runs more risk even with good tools
    and even if you have just cleaned the tool out.
     
  13. Al

    Al Guest

    I've used a Dremel tool to remove relays, as well as other components, by
    cutting them to pieces, carefully, of course. Then I unsolder one pin at a
    time. Unless you need to do failure analysis on the bad part.

    Al
     
  14. Guest

    Which bit do you use? A grinder or a saw bit
     
  15. Guest

    Cutting off the relay is the hard bit, as many have quite hefty bits
    of steel in them. A cutting wheel in a die grinder (aka dremel) works,
    but can be slow.


    NT
     
  16. Ron(UK)

    Ron(UK) Guest

    My own method would be a good hot iron, plenty of solder braid and a lot
    of patience.

    Ron(UK)
     
  17. Steve

    Steve Guest

    I've often found that in a pinch, you can wick the solder out, re-fill
    the holes with new solder, re wick the holes. Sometimes the
    re-filling process can reflow the whole joint instead of wicking out
    the top half and the bottom never gets hot enough. Of course, not
    perfect, and should be done on a scrap board.

    Steve
     
  18. Ron(UK)

    Ron(UK) Guest

    That`s true. One of the things novices do wrong is to wick off most of
    the solder, but leave a little behind deep in the hole, that wont be
    drawn up into the solder braid. Then they get impatient and try to rip
    the component out damaging the board in the process.

    There needs to be enough solder to easily wick up into the braid, and
    the iron need to be hot enough to melt all the solder in the joint
    through the braid or there`s a chance that pulling the braid away takes
    some of the pad with it.

    There`s as much an art to desoldering as there is to soldering. (IMO)

    Ron(UK)
     


  19. The solder used for wave soldering is 80/20 and has a higher melting
    temperature. By removing what solder you can, then adding fresh 60/40
    you move the melting point to somewhere in between, which then can be
    either vacuum desoldered or removed with solder wick and a drop of
    liquid rosin flux.

    80/20 is used for wave soldering, because it has a very narrow
    temperature range where it is in a plastic state. this reduces cold
    solder joints, by not giving the leads a chance to move while the solder
    passes through this state.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  20. Smitty Two

    Smitty Two Guest

    80/20? 60/40? What kind of solder are you talking about? Eutectic
    tin/lead is 63/37 and used in both hand and automated soldering.
     
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