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I have seen videos on youtube with some guys using hot air pistols (or even small propane burner with bunsen flame) to desolder the components from a PCB. The job is done REALLY quick! The components were really hot. They were still handling the components with gloves, many seconds after they fell from the PCB. My question is: can the components survive this kind of treatment.

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  • \$\begingroup\$ The temperature range for most components will be in the data sheet. Question is meaningless, unless the temperature is known. \$\endgroup\$ – Leon Heller Apr 10 '15 at 8:23
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    \$\begingroup\$ @LeonHeller: then you must add it is meaningless unless all the specific components are known. You don't need a degree in psychology to read out of the question that the OP thinks the temperatures are way too hot and is really wondering under what conditions it can work, since he can not deduce from the videos what temperatures these parts are. \$\endgroup\$ – PlasmaHH Apr 10 '15 at 8:31
  • \$\begingroup\$ @LeonHeller - I know that. It would be faster to unsold the components one by one (manually, at safe temperature) than to read the datasheet for EACH component you want to desolder. So, in THIS context, your answer is meaningless. Don't get me wrong: I agree with you. You cannot know the exact answer until you read all data-sheets and follow the soldering conditions by the book!!!! But this is not 'batch desoldering' anymore. Right? \$\endgroup\$ – WeGoToMars Apr 10 '15 at 8:39
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tl;dr : It depends.

I think you are referring to the method of heating things up with a hot air gun, and then shaking the pcb so everything falls of, or a variation of this.

First of all, remember that the process of actually soldering SMT PCBs is quite similar. Stuff goes into a reflow oven, heats up until solder paste melts to liquid solder, then cools down.

But of course, this is a much more uncontrolled thing when using a heat gun. It will depend on:

  • How much the heat gun heats the parts (here really the inside temperature matters most)
  • How much humidity has accumulated in the parts
  • For how long the parts are exposed to the temperature
  • The specific thermal properties of a part.

For the last point, you can look at a datasheet of a specific part, especially at the reflow profile. Controlling temperature and exposure time is next to impossible with a heatgun, and when the parts are sensitive to being heated up while containing humidity, they are toast.

So it all depends and is mostly luck and statistics. When doing it by people with some experience in the process, the yield of functional parts can be way over 80%.

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  • \$\begingroup\$ Thanks PlasmaHH-80% is not bad at all. What is BAD is that you have 20% chance to use one of those fried components :) :) \$\endgroup\$ – WeGoToMars Apr 10 '15 at 8:41
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    \$\begingroup\$ @Altar: A much saner alternative would be to try estimate the used reflow profile, build a reflow oven that holds the PCB upside down and vibrates it, and put things in there... but still due to the moist issue this will not be guaranteed to yield 100%. Plus you have all kinds of problems with this approach and TTH boards/components anyways. \$\endgroup\$ – PlasmaHH Apr 10 '15 at 8:44
  • \$\begingroup\$ oh... no... this is just for hobby. not industrial level :) \$\endgroup\$ – WeGoToMars Apr 10 '15 at 9:05
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    \$\begingroup\$ @Altar: For a hobbyist I recommend having a bin of organ donor PCBs and desolder when you need a part. Much less time, higher yield and it gives an opportunity to learn what kinds of parts are used on what kinds of PCBs. \$\endgroup\$ – PlasmaHH Apr 10 '15 at 9:08

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