Safe temperature for desoldering SMD components w/ hot-air rework gun?

Question

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.

Answer 1

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.

Answer 2

I am working with SMD for a while and I suggest you use leaded solder to treat the oxidized solder joints with flux before you get to the hot air stage. After solder mixture process, preheat the board close to 200C and continue with hot air station. I use analog hot air stations because I don't want to turn around and look at the temperature. I know where I have to set the hand dial without looking and I think that is between 7-8 on Hakko 852 station (around 420C). Preheat the chip from distance and can feel when it is enough to start. I count to 5 and viola pull the chip out without any problem. The hard ones are BGA chips and need precision timing and good BGA preheater. Average ICs are rated to 380C/10Sec I think but I am not sure.

Answer 3

Pre-heating at 200 degrees Celsius for 1min, then raise temperature to 400 degrees Celsius to heat for 20sec. You can use a thermal couple to monitor the temperature.

Answer 4

If you just bought it (or replaced the element), some stations will need calibration. (ALWAYS check). If your unit has potentiometers on the front use a non inductive screwdriver. Otherwise look for a calibration mode. Search: "rework station calibration" or "rework station calibration mode" Harbor Freight tools has a infra red temperature probe for $20.00. -Should do the trick. When I unboxed mine, it was 100c out. -e

Answer 5

preheat your pcb to 150c. Use Chipquick alloy or Zephertronics Lo melt. Apply flux, lomelt let sit for about 4 mins then lift the chip off the pcb. Use flux and a swab to gather and remove the leftover lomelt