Choosing a hot air gun

[Pentium100]

Hi, replacing capacitors in a motherboard and SMD devices in general is probably much easier with a hot air gun instead of a regular soldering iron. I though that the hot air guns were really expensive but then Dave mentioned in a video that his gun was about $50, which is within my price range. So, I decided to buy one. However, as I have never used such a tool, I do not know how to understand the specs. For example - do I want more airflow or less?

Can anyone explain to me what to look for when choosing a hot air gun. I do not have a lot of money, so I'd say $100 would be the upper limit for price. I am planning to use it to repair devices (replacing parts, like capacitors in a motherboard, not soldering parts on a brand new board, so the tool has to be good enough for desoldering as well as soldering).

[Psi]

You would think replacing throughhole caps on a motherboard would be easier with a hotair gun. However it isn't, it takes ages to heat up the board.
I made that mistake too.

They're awesome for smt work though.

The best thing for replacing motherboard caps is a HUGE iron tip that can touch both legs at once. Then you can just wait a few seconds and pull the whole cap out in one hit.

Then use a spring loaded desoldering tool to try remove solder from the holes. Note: you will find one hole is easy to clear of solder and one is almost impossible. (ground or power plane)
That's just fine, you only need one hole clear anyway.
Cut the new capacitor leg length so that the leg to go into the clean hole is 5mm longer.
Push the capacitor in until the other leg touches the unclean hole. now heat up that hole from the other side while pushing the cap a little and it will pop in all the way.

Now solder both holes properly and cut the excess legs off.
Done.

[T4P]

Usually the brushless ones have more airflow than the pump-types plus they're easier to repair if the fan does breakdown
1) You can dip the fan's airflow of course
2) Of course all of them are good for desoldering SMD!, you just use the two forked thing they give to nudge the desoldered part out

So that's pretty much all, if Atten 858D still works for him, then great.

My (YiHUA, not the difference) 858D failed within a month because of piss poor thermal management

well one thing's for sure is that you really shouldn't try to use a hot air station to desolder TH caps, but use a desoldering station's much easier

[Pentium100]

Thanks for the advice. I had trouble sucking the solder out of the holes with a desoldering tool like in the attachment - a little bit of solder just stuck somewhere and refused to melt.

I guess I need to buy a powerful soldering iron with a big tip (for TTH components) and the hot air gun (for SMD components).

[Psi]

Add more solder to the joint before desoldering with a vacuum too. It provides more thermal mass so it stays molten longer and allows the tool to get more solder out.

Another trick you can do, if the joint is still being held by a tiny bit of solder, is to heat up just the pin with your iron and wiggle it back and forth a couple of times using the very tip of the iron. The goal is to have the solder re-solidify while the pin is still moving.
If there's only a tiny bit of solder holding it this will prevent it from re-joining to the pin and it will be free to move when cold.

You don't need to go crazy wiggling the pin back and forward, only a few tiny movements are needed, if the pin is held by solder it wont move at all. Remember, you don't want to 'bend' the pin, only get it free to move.
If you go crazy bending it back and forward it will eventually break from metal fatigue.

Once you can move the pin easily while cold you know it's free and you can move on to another pin.

When you have all pins doing that pull on the IC or device a little and, if it wont come out, clean the iron well so there is no solder on it and touch the iron around the various pins while pulling. Eventually you will hit on the one holding it in and the device will come out.

Remember to re-tin the iron after, you don't want to leave the tip with no solder on it.

[notsob]

Have a look at badcaps.net - some info there on removing CAPs from motherboards, note the method of using a dental type stainless pick.