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I'm currently repairing smartphones and I usually desolder some components from damaged phones for later use as a replacement.

I usually use hot air for the task. But when trying to remove small push buttons with some plastic as a part of the button's body, I partially melt the plastic due to heat.

What is the best way to desolder components like 4 pads smd push button without melting the plastic and damaging the button?

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    \$\begingroup\$ What temperature are you using? If they were soldered without damage they most likely can be removed without damage as well. A few techniques you can try is adding regular 60/40 solder to try to lower the melting point of lead-less alloys. If you want to be more agressive on the melting point reduction path, you can try IC remover alloys such as "ChipQuik". \$\endgroup\$ – Wesley Lee Sep 11 '16 at 23:35
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    \$\begingroup\$ To give the answer you probably don't want: you don't keep those components. They're likely damaged by rework, even if it's not visible from the surface of the component. Most components have had their heat stress rating met during the initial manufacturing process. It's best practice to use only new components to replace a reworked part. \$\endgroup\$ – user2943160 Sep 11 '16 at 23:44
  • \$\begingroup\$ Perhaps with a tip such as this? \$\endgroup\$ – rdtsc Sep 12 '16 at 1:18
  • \$\begingroup\$ Some surface mount components will come apart so easily that the touch of a soldering iron, at molten-solder temperatures, destroys them. Been there, done that. \$\endgroup\$ – Whit3rd Sep 12 '16 at 2:02
  • \$\begingroup\$ Thanks there are some really good answers here... Chipquik is something i may try for some higher price components and is defenitely the best method but pricey indeed \$\endgroup\$ – Latchup Sep 12 '16 at 7:12
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I've used the ChipQuik alloy that Wesley is talking about and its good. Another low-tech method is to apply a fine soldering iron tip at the switch pins and once the solder melts lift the pin ever so slightly and slip in a piece of paper between the pad the board. This ensures that the pad does not reattach when you are doing the other pads. You'd think the paper would burn but it does not, atleast not to the point where the pin burns through the paper and reattaches to the pad.

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