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Advice on heat gun temp for de-soldering

  1. Jun 2, 2016 #1
    This is more of a general question about what temps you set your hot air gun. I just got a new rework station and messed around with it for a bit on a old PCB removing large and small components. I find it easy to damage the PCB. In general I tend to solder pretty hot, anywhere from 300C to 400C and am not having any issues. I don't work much with solid state so my needs are for mostly for tube amps and old radios.

    If I need to remove a small relay or opamp for example, is it better to use higher heat or use lower heat and heat things up slowly?

    Thanks,

    Billy
     
  2. jcsd
  3. Jun 2, 2016 #2

    phinds

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    None of the above. Heat gun seems like a terrible idea for de-soldering. Get some solder wick.
     
  4. Jun 2, 2016 #3
    I use solder wick from time to time but use one of several solder suckers more often. The relays are 10 pin and are very hard to remove at times. The pins are very small and it is very hard to remove all the solder from around the pins. 18 pin IC's are even harder to remove at times if the pins are almost the same size as the hole.

    Thanks,

    Billy
     
  5. Jun 2, 2016 #4

    phinds

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    Yeah, solder suckers are also good. I would just worry that a heat gun could damage components ... not localized enough.
     
  6. Jun 2, 2016 #5
    I have 10 or more tips for the heat gun, some round some square and some rectangle to localize the heat. I will continue to de-solder stuff on the junk PCBs until I get it figured out.
    There is a de-soldering pistol also on the new re-work station but it looks kinda mickey mouse. I have not tried it yet. It also works with hot air but has a very small tip useful for de-soldering single pins I guess. It has a built in solder sucker but not much suction.
     
  7. Jun 3, 2016 #6

    dlgoff

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    Heat gun? :oldeek:
    For most everything electrical I solder, whether it's new construction or repair, I do with a 25 watt iron, damp sponge, and solder flux. By keeping the iron's tip clean/swiped, fluxed, & tinned, (after and before each operation); not allowed to oxide, I get all the thermal transfer and temperature needed for a good solder flow. Just say'n
     
  8. Jun 3, 2016 #7

    phinds

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    Yeah, me too (although I often use a folded paper towel in place of the sponge), but what does that have to do with desoldering?
     
  9. Jun 3, 2016 #8

    dlgoff

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    Good flowing solder is easier to remove. If the board can be held in my hand, I add solder then give a quick rap of it's edge on the bench. Works quicker and removes better than a solder sucker.
     
  10. Jun 3, 2016 #9

    phinds

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    OK, I'll buy that. I only used the "rapping" method early on. I always thought dewick was a better way to go. I absolutely agree w/ you that a good flow on makes for an easier removal.
     
  11. Jun 3, 2016 #10

    dlgoff

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    Never really used it much for dewicking but I do remember using it to repair/replace large traces. :oldbiggrin:
     
  12. Jun 3, 2016 #11

    phinds

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    I never make big enough mistakes to need that.:oldlaugh:

    I vaguely remember now that the instructor, when NASA sent me to soldering school in about 1963, was adamant about not doing any rapping but he was a bit of a stick in the mud and also didn't much care for solder suckers either. He was a dewicker all the way but I think you get a slightly shorter heating time with a sucker so less chance of component damage. I don't think they had suckers when he was young. I do agree w/ him about the rapping method though. I remember thinking it really WAS a bit problematic when I tried it (I was probably overcautious).
     
  13. Jun 3, 2016 #12

    dlgoff

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    Oh. These weren't mistakes. :oldgrumpy:
    Circuit boards are babied to much IMO.
    Agreed. But rapping is better IMO; as long as you flux then add solder. The more melted solder mass you have (up to a point), the cleaner and faster it gets removed.
    Me either old man. :angel:
     
  14. Jun 3, 2016 #13

    phinds

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    Sure they weren't :smile:

    Yeah, as I said I was probably being too cautious.

    Sure, but that's the same thing w/ a sucker.
     
  15. Jun 3, 2016 #14

    Averagesupernova

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    Everything I have to say about it is probably covered in the following threads. I would not ever be afraid to use the appropriate heat gun to do the appropriate task. Common sense goes a long way of course. For example don't try to desolder polyethylene capacitors with a heat gun. Know what kind of device you are working with and how much heat it will take before proceeding.

    https://www.physicsforums.com/threa...-components-from-a-board.699032/#post-4429580
    https://www.physicsforums.com/threads/question-about-the-pic-soldering.789681/#post-4960645
    https://www.physicsforums.com/threads/chip-harness.171565/#post-1340529
     
  16. Jun 3, 2016 #15

    dlgoff

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    Blown traces, not soldering mistakes. IIRC they were repair jobs on equipment while I was employed as a biomedical engineer at the KU Med Center in Kansas City. However, I'll admit the I've lifted a few traces on cheap single-sided Phenolic paper boards.

    Agreed. Good results come from experiences.
     
  17. Jun 4, 2016 #16

    Baluncore

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    I sometimes have to remove multi-pin or multi-pad devices from PCBs. After much experience I have developed a low-tech way that works well for me. It involves several distinct steps.
    1. Add more compatible low temperature solder to bridge all the terminals with a normal iron and tip.
    2. Use a specially shaped “tip” that can heat all terminals at the same time. The excess solder evenly spreads the heat.
    3. As the last solder melts lift away the component.
    4. Use a very gentle form of the rap or a solder sucking tool to remove excess solder from the component terminals and from the PCB.
    5. Use solder wick to remove remaining solder from PCB pads, holes and component pins.

    To remove solder from plated through holes I use the side of a sharp pointed tip to press solder wick into the hole entrance, then I vibrate the wick by stretching and compressing or by moving the tail of the wick in a small circle while maintaining the temperature. That movement draws all the solder out of the hole and moves it along the wick. If you cannot get the last solder out of a hole at the first attempt, then resolder it and try again. It comes down to heat flow and that requires solder. Failing that, a tinned copper wire soldered into, then pulled through the hole will carry away the unwanted solder.
     
  18. Jun 4, 2016 #17
    I have read all the threads here and other places. There seems to be some general agreement for temps for soldering in the 300 to 400C range.
    Searches for hot air heating seem to be less in agreement. Some suggest pre heating to 200C then going to 400C for the last 20 seconds or so.

    In general I am NOT trying to save a component but replacing a failed component. In general I am NOT dealing with multi pin ICs other than 8 pin opamps which are not a problem to remove.

    What I am having issues with are 8 pin relays which have round pins which fit pretty tight in the round holes in a PCB with little room for the solder to begin with. These relays are soldered to PCBs which have traces on both sides of the board and it is very easy to damage the traces. Best case is that all pins are heated at the same time and that is the reason for wanting to use hot air.

    My question is which is better to pre heat or not. If not what is a good starting temp?

    Billy
     
  19. Jun 4, 2016 #18

    phinds

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    Yeah, I'd forgotten all about those little devils. Very handy, as you point out.
     
  20. Jun 4, 2016 #19

    Baluncore

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    I am sure that hot air works well with paste soldering surface mount because you can see it happening and synchronous timing is not important. I tried hot air for component removal 20 years ago and gave up on it. The exposure of different pins to hot air is too variable and uneven. A single bridge or pool of solder brings all the leads to the melting point at the same time.
     
  21. Jun 4, 2016 #20

    dlgoff

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    If there's a way to clip (with small side cutter) the relay off the board (?), then it's easy to then remove each pin left in the board.
     
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