are QFN scary

[OhYou_]

I'm at a tipping point in a project where I've just lost motivation because it got quite complex and now I have a bunch of stupid QFN chips and other stuff that I've never worked with. 

Just looking at them makes me sweat a bit. 

I also would probably try to hot air them on but I would really have to build a vapour phase setup for it, which is fine because the board is credit card size. 

 

for the project, the problem is I am trying to implement usb 3.0 gen 1 and usb PD, and leave the possibility for displayport and aux dp. 
I would fit two type c receptacles. 

OR, i say sod all that and just put one usb 3.0 type A port and be done for 3/5 the bom cost and zero added equipment cost. 

[ImorallySourcedElectrons]

Other than the expense, Gladen is also a complete nightmare to deal with, it will turn anything it comes into contact with into a non-stick surface for the foreseeable future and you need specific solvents to clean it up. And it's handled as dangerous waste in most jurisdictions because it basically doesn't decompose naturally. So you got to get it handled as chemical waste if you follow proper procedures.

But in terms of soldering QFNs, vapour phase ain't necessary for QFNs. We sent them off all the time for assembly in hot air convection or infrared ovens, and did plenty of them in the lab with a hot air rework station while prototyping. If you want to do them manually, apply plenty of no-clean liquid flux, put a fine line of solder paste across the pads on each side, place the QFN aligned to the silkscreen markings, heat up the PCB to about 80-90°C on a hot plate and then hit it with the hot air. You can also do them with a manual soldering iron if you must, though you want the pads sticking out a bit from the side to do that.

[mariushm]

Plenty circuit board manufacturers will give you the option to add a steel stencil to your pcb order (even cut it to size you want for you if you make a note).

I know for sure JLCPCB has the option, costs 7$ for a 2 layer board, even if it's 300 x 300 mm 

PCBWay seems to offer stencils from around $10.

 

But if you have the boards already with parts applied it's still easy to solder QFN ... use a gel or liquid flux, apply over the pads, then use soldering iron with a cup shaped tip  - type E below for example but type A could also work - to drag solder over the pads to tin them. 

Then you can cover sensitive parts around with some kapton tape, apply more liquid /gel flux, put the QFN part down and use a hot air gun to heat up the chip are get the solder flowing under the chip.  Could probably also solder it using the type A tip by heating each "pin" and pad to get the solder flowing.

If you don't have hot air gun and the center pad has solder, you can apply some liquid flux on the bottom of the chip, heat that solder with your iron until it's liquid and quickly put the chip down on the liquid solder and then use some tweezers or something to gently press on the chip and align the pads all around and solder a corner pin to align the chip.

 

 

 

See picture below or https://tameson.com/soldering-iron-tips.html