QFN package soldering should be a very difficult thing if you don’t do any optimized work on it, all the pins of this package and hidden below the package. It is no way to reach it and check it, except precise machine work.
So how can we optimized the package to improve the DIY soldering capability, let us take a example of CP2102 IC.
The orginal IC package looks like below, and you can see the SMD pins are under the IC:
And then we change it into this:
Except the top layer you should change, but also the “tcream” and “tstop” layer which is for the SMD pads. (Sufcceed work in the picture above, with tilted cross line is the layer tcream and tstop). If you forget, then it wil look like this (No long enough cross line retangule box):
Now in the physical work, everything get easy and clear! During your prototype, you can use the syring soldering paste to have it done easily.