Electronics > Beginners

Hot air soldering, what am I doing wrong?

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TheHolyHorse:
Hi, so I'm working on a project that has an LQFP48 package. It needed replacement so I de-soldered it and though I'd use the hot air to get it back as well, because it's a pain in the ass to use the iron with all the other stuff in way.

So now to the issue. I've been watching a bunch of videos of people soldering QFN QFP etc with hot air and the chip just gets suck in place no problem. But that never happens for me. I add solder to the pads and a bunch of flux, but the flux burns up before the solder even melts so I think that's why it doesn't help me and it doesn't help that I'm shaking like a leaf.

But how do other people do it? What am I supposed to do to prevent all the flux from burning to early?

I'm truly lost :-//

TomS_:
Is the part not sticking or blowing out of the way? Maybe too much airflow, or holding the gun to the side instead of top down? Dont get in too close too quick, the component and the surrounding board need to soak up some heat first, so take your time.

Ive seen people prod the part with tweezers etc once all of the solder has melted, but I couldnt honestly say I would do that if it has self centered.

What sort of flux are you using, is it a "paste" or liquid? How much are you using?

You could take a look at Louis Rossmann on youtube. He would seem to have even BGA reflow down to an art, and does not spare the flux. Even with the amount he uses, it almost all disappears before the soldering process is complete.

So probably it will all dissolve before the part solders, but that should be fine as it is only needed to clean the surfaces to be soldered, not make the solder melt or form joins (except by ensuring the pads/leads etc are clean of contaminants etc).

I havent personally done any hot air reflow, but I have also watched a few videos and other people that do it, and Im picking up bits and pieces I need to give it a go eventually. For now I use drag soldering and that seems to be working just fine for me.

madires:
Take some e-junk, practice and figure out which settings of your hot air station work best. Flux is meant to remove oxidation and needs heat to do its job. So it will evaporate during the whole process and leave some residue. The solder's surface tension is what drags components into position.

kripton2035:
may be you're using too much air flow ? try half the max value to see if the chip stays in place.

xmetal:
Using leaded solder helps as the chips tend to jump in to to place compared to lead-free. Also it melts at a lower temperature than the latter.

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