Removing and replacing surface mount capacitors - tips needed!

Discussion in 'General Electronics Chat' started by MrSoftware, Nov 12, 2015.

  1. MrSoftware

    Thread Starter Active Member

    Oct 29, 2013
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    Can anyone give me tips on removing surface mount capacitors, without lifting the traces off the board? And when it's time to put them back, what's the best way to melt the solder?

    I'm attempting to fix a dead APC RS1500 UPS and I've discovered that a bunch of the surface mount capacitors are dead, but they're a bugger to get off. Using the iron, I can only heat the edges and the traces underneath are lifting off. Using hot air, the cap gets blazing hot (320C) and as best I can tell the traces are still coming up. Is there a secret to it? This has to be one of the most delicate boards I've played with, it's like operating on wet paper towels.

    Also when it's time to put these things back, will it kill them to be in 320C air long enough to melt all the solder? Or should I just tack the sides with my iron?


    temp.PNG
     
  2. MrSoftware

    Thread Starter Active Member

    Oct 29, 2013
    501
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    On the up-side, replacing the traces with solder seems to be going OK on the few I've tried, not sure what it's going to be like to solder to when the new caps arrive:


    temp.PNG
     
  3. KJ6EAD

    Senior Member

    Apr 30, 2011
    1,425
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    Solder tweezers work well for removing and replacing chip capacitors. If you don't want to spend the money on that tool, using two irons also works fairly well.

    To install the new component, clean one of the lands well with solder wick and use the residual solder on the other land to tack the part. Solder the untacked end, then add new solder and/or flux as needed on the tacked end to finish.
     
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  4. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,145
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    Can you remove the caps destructively? Then unsolder the pads.

    Soldering with paste rather than solid solder should be straightforward.

    Other techniques might include pre-heating the other side of the board.
     
  5. bwilliams60

    Active Member

    Nov 18, 2012
    722
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    When removing the old SMD caps, touch your iron to one of the pads and melt some new solder onto it. Immediately after, touch the other pad and make it puddle. Take your iron across both at the same time and sweep the SMD off the board. You should be left with two pads with a small amount of solder on each.
    Best bet is hot air gun designed for SMD if you have one. Should come off very easily. One other method is to purchase tweezer like iron such as:
    http://www.ebay.com/itm/NEW-USA-GQ-...-station-hot-air-soldering-Iron-/121005904954

    Good luck
     
  6. cmartinez

    AAC Fanatic!

    Jan 17, 2007
    3,573
    2,539
    For me, the easiest way to do it is to use two soldering irons simultaneously, left and right hand, pressing each side of the cap, and then simply lifting it off the board..
     
  7. MrSoftware

    Thread Starter Active Member

    Oct 29, 2013
    501
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    Thanks everyone for the replies, I'll give them a try. Breaking them up, and heating from the backside are interesting ideas. Also I've got 2 irons, I might give that a try too in lieu of the tweezer iron, that thing looks cool. I do have hot air and that does remove them pretty easily, but the tracks still seem to come up. Maybe I've got it too hot at 320C? Also will the hot air be too hot for putting the new ones down?

    @bwilliams60, thanks for the tip but these are the can type and I can't get one iron touching both pads at the same time. But I bet your method would work good on the smaller ones.
     
  8. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,052
    3,817

    To remove them, you can clip them in half with a clipper - then desolder each half more easily.
     
  9. dl324

    Distinguished Member

    Mar 30, 2015
    3,243
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    Just make sure the solder on all leads is completely molten and pick the parts up with tweezers, taking care not to move the pads/traces as the adhesive may let them move. If they move, move them back into place with tweezers and let the adhesive cool.
    Not if you get the components soldered in less than 10 seconds.
     
  10. tindel

    Active Member

    Sep 16, 2012
    568
    193
    For chip caps I usually add a bunch of solder to both pads, bridge my iron across the part and the iron usually picks up the part. If the iron doesn't do it, I have a good set of tweezers nearby to pull off the part. Usually when parts are placed there is so little solder that when you do flow the solder the surface tension is huge, so adding solder helps reduce the surface tension.

    For the caps you pictured, I haven't dealt with them, but what I would try is adding a bunch of solder to each pad and then try to lift one side and then the other and go back and fourth until it finally comes up.

    Reducing surface tension is key when removing SMT parts.
     
  11. MrSoftware

    Thread Starter Active Member

    Oct 29, 2013
    501
    123
    Thanks everyone. After trying several things, what worked best was adding solder to the sides to conduct heat, then with my iron on one side gently lift that side with tweezers, then move to the other side and repeat. Without adding solder I couldn't melt all the solder under the caps, but adding solder did the trick. Then I used the solder sucker to clean up any extra. To replace the caps I added some solder to the pads, added some flux then pressed down gently with tweezers while alternatively heating each side, and presto they would mount flat.

    Cutting the caps did great at getting me to the pads, but I wasn't prepared for how much juice comes out of the caps when you cut them open. ;)
     
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  12. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    new solder and a powerful 50W iron will do the job. if traces just lifted off, press them down again when theyre still hot.

    Multilayer boards are a pain though.
     
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