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Hot air soldering beginner - any tips and tricks?

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shadewind:
I just got me a hot air reworking station which I'm going to use to solder exposed pad devices and QFN devices. Since I don't have all the parts for my current project yet, I decided to test it out by removing some parts off an old useless graphics card and it seemes to work pretty well. I have a few questions though:


* I used a temperature of somewhere around 300 to 350 degrees C. Is this an appropriate temperature or should I use something lower? I guess it depends on what you're doing but some pointers would be nice. I noticed that for parts containing plastic (in this case a PLCC socket) I had to use a lower temperature to prevent the plastic from melting (about 260 C).
* I wasn't able to remove the GPU itself which was a rather large QFP device since I didn't really come up with any way to heat all the sides at the same time. Aoyue has special nozzles for this that are square shaped. Is this required or is there some trick I haven't figured out?
Any additional tips and hints would be very much appreciated.

IanB:
I have no practical experience in this regard, so take what I say as purely theoretical.

For installing SMT devices it might work better to use a soldering iron rather than hot air. Hot air might best be reserved for unsoldering and reworking previously assembled parts. See these videos on selection and use of tip shapes by Hakko for examples of SMT soldering:

http://www.hakko.com/english/tip_selection/flv/tip_movie.html?id=d-1

For removing larger parts, preheating of the board is advised. A specialized board preheater can be used, or it can be improvised for example with a coffee cup heater.

Also for removing large parts, a bigger source of hot air might help, for example a hot air gun for heat shrink tubing or embossing. You can protect the surrounding parts with aluminium foil with a hole cut in it to expose just the part you want to remove.

shadewind:
I do know how to solder SMT parts with a soldering iron, that's not problem. But you can't (at least not most of the time) solder QFN and exposed pad devices properly without hot air or other reflow technique since you can reach all of the pads with a soldering iron.

IanB:
Right, I didn't pay proper attention to QFN in your post.

But I do believe a preheater is a big help. It avoids undue stress on the board and it leaves the hot air gun with less temperature rise to achieve.

sacherjj:
Biggest thing is to use plenty of flux.  Solder paste.  Go at it.  I've really found it easier than normal soldering and parts self align very well.

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