Desoldering SMD – Safe Temperature for Desoldering SMD Components with Hot-Air Rework Gun

hot-airsurface-mount

What is a reasonably safe temperature to use for desoldering SMD components using a hot-air rework gun? I have a new-to-me rework station from Xytronic and the documentation clearly assumes you know what you're doing… It tells you what temperature range the gun is capable of, but has nothing to say about where you should be setting it.

Also, I was surprised by how little air pressure the unit generates even when the AIR setting is set to max (99). Is this normal?

My one test so far was to desolder a random surface-mount IC package from a piece of electronic salvage I had lying around (kept for exactly this purpose). I tried to step up the temperature slowly, but I got all the way to 400 degrees Celsius before the chip seemed to suddenly be floating free. I never did see any visible change in the solder… (But perhaps that's just my eyesight.)

I am concerned that at that temperature any component that I can get off a board might be damaged by the heat.

Best Answer

Very good idea to practice, practice, and practice some more on salvaged boards until you get competent with new tools. You didn't notice the solder had reached the molten state because there's so little of it used to solder components.

The typical lead-free solder has a melting point around 217 degrees C, so you'll have to get the leads and pads up to that temperature before trying to remove the component. The reason why you need a much higher temperature is because you want to get the solder joints to the melting point as fast as possible. If the hot-air gun is set to a much lower temperature, it'll take a longer time to reach the melting point. The longer the time to raise the temperature of the leads/pads will increase the overall temperature of the component, possibly past the point of destruction. So the technique is to heat it up fast, remove the part and hot-air gun, then put the part where it can cool off.

Now, if you're removing a part that's already fried due to some other reason, no worries then. Just don't damage the board by overheating the pads and causing them to lift off. If that happens, your headaches are just beginning on this repair.