Hot air soldering, what am I doing wrong?

[Jwillis]

Have you tried Preheating the board. I've only done a couple because like you I shake a lot . But I did find that heating the entire board in the oven to around 200 F help me.  Or, if there's  a lot of plastic that could get damaged , preheat locally where the chip is to be welded .Check out PCB preheating for a proper procedure since I'm a real novice at SMD soldering.

[agehall]

Just use better flux. I use the Amtech stuff that Louis Rossmann uses and it is just awesome. Kind of hard to get hold of in the EU though so I usually stock up whenever I pass by NYC.

[TheHolyHorse]

Seems like getting some good quality flux and pre hearing the board is the way to go.

Thanks for all the support

[hermitengineer]

Just a beginner with QFP myeslf, and reflecting on my many failures before giving up and getting TSSOP versions, but I wonder if one of the major problems when hand-soldering them is that you don't get an even amount of solder on each pad?  Some will have plenty of solder and others... not so much.  So when you heat the chip up and even get it to stick in place after the solder melts, you still might end up with unconnected pins.  Or at least, I almost always did     The tweezers probably do help in that area though, as they will squish some of the (hopefully not egregious) excess solder out and make sure that all pins get at least some solder bonding the chip to the pad when it cools.  I wasn't trying the tweezers at the time other than to hold it in place, so that's just my speculation.

The other issue is when it has the middle pad, because it requires "just enough" solder.  Not enough, and the pad can't act as a good heat sink.  Too much, and the chip just floats on the middle pad.

[iMo]

You do not bother with soldering individual pins (smd flatpacks). You put a lot of solder flux (the amtech 223 gel for example) - such the pins are fully covered by it, put a bit of solder on the iron tip, and run with the tip over the pins (while the package is positioned at the pcb pads properly - you must fix the package to the pcb with a solder blob put somewhere on the pins at the opposite package side).
Many pins will be soldered together (sometimes all). Then put again a lot of flux at the pins, take the "copper wick - desoldering braid" and place the wick at the pins (wick must swim in the flux), heat up the braid from top with iron tip such the wick starts to suck in all the excess solder - you move the wick (together with iron tip) slowly over the pins.
In one single move you get perfectly soldered pins, even they are 0.5mm pitch. Use a LOT of solder flux (all must swim in the flux), otherwise the pins stay shorted or not soldered properly.

[Jwillis]

Interesting discussion all around .I found this method but haven't tried it myself and was wondering if anyone here would have any input .

[KL27x]

hermitengineer:

Just a beginner with QFP myeslf, and reflecting on my many failures before giving up and getting TSSOP versions, but I wonder if one of the major problems when hand-soldering them is that you don't get an even amount of solder on each pad?  Some will have plenty of solder and others... not so much.  So when you heat the chip up and even get it to stick in place after the solder melts, you still might end up with unconnected pins.  Or at least, I almost always did     

The other issue is when it has the middle pad, because it requires "just enough" solder.  Not enough, and the pad can't act as a good heat sink.  Too much, and the chip just floats on the middle pad.

Imo it sounds like hermitengineer is talking about hot air reflow.

hermitengineer:

The tweezers probably do help in that area though, as they will squish some of the (hopefully not egregious) excess solder out and make sure that all pins get at least some solder bonding the chip to the pad when it cools.  I wasn't trying the tweezers at the time other than to hold it in place, so that's just my speculation.

Yes. I like to err on too much solder than too little. The excess just squishes out and stays out. If this squeezeout is too ugly or causes a bridge, then I would have to go over it with a soldering iron. But if you start with too little, then the chip suctions to the center pad and doesn't align itself. It will take a hard nudge with tweezers to move it, and where it stops will be random.

If you don't have to solder the center pad and the part has "side pad," I personally find it to be faster/easier to use an iron to solder the outer pads vs hot air reflow.