Is hand soldering a 48-VFQFN possible? I could not find any videos on this and I guess it must be quite hard.
It 's possible by hand when you're very experienced with fine hand soldering, but for lesser souls it's also possible with solder paste and manual reflow with a hot air (rework) station.
With reflow, the part will align itself and solder will 'suck' towards the pins and pads.
Yes, I have done it. I use a lot of flux for delicate solder jobs and to check the pad alignment I have a small USB microscope so I can check all sides without having to move the PCB.
I put a tiny bit of solder on one pad. Then a bit more flux and last the chip on top. Check with the USB camera and push the chip so all pads are aligned. Then I only have to heat the solder and not mess with a soldering iron AND solder wire.
It's quite possible to reflow QFNs (even those with a big thermal pad) without any special tools or materials: Just a soldering iron, solder wire, flux, and a kitchen stove.
- Tin the pads with a layer of solder of consistent thickness.
- Apply flux and align the chip
- Place the assembly on an old frying pan or directly on a hot plate, and crank up the heat until the solder melts and the surface tension pulls the chip into position.
- Remove the board and let cool to room temp.
Obviously this only works with boards that only have components on one side. I wouldn't use this for any production boards, but IMO the results are still better than a hand soldering attempt.
Hand soldering QFN chips is difficult, but can be done with fine solder and a small tipped iron. The standard footprint (intended for paste) needs the pads to be extended.