Packs of SMD ICs like QFN ,DFN have pins embedded to the plastic body.
So as you place the IC on the board soldering appears to be difficult.
why ? because u cant align the ic pin by pin easily as pins are hiding below.
,a slight 10 degree misalignment will result in bridge of solder .
The steps elaborate the trick to perfectly align the chip and hand solder .
Read the link below before doing this..
My instructible is inspired by :https://www.instructables.com/id/hand-soldering-teeny-tiny-chips!/
Step 1: What Tools You Need
A fine point soldering iron cheap ones will do, fine solder wire low melting type (180deg ) like WBT.
(This will make the task easy),cleaning sponge , paste flux,tweezers.12x magnifier
if you have good eyes u can manage without it .
One strong LED light 1 -2 cm round preferred. I used SE w810i mobile phone LEd light.
other tools like helping hand etc.
Step 2: Place the Ic Properly
There is a dot indicating pin 1 . Check the proper placement from the documents you have or your pcb design.
Flux the IC pads on PCB. Add a little solder to each pin pad at the PCB .When done, Put a little flux to all pads again.
Add little solder on IC pins too .
TIP: Use very small amount of solder , clean the pins with PCB cleaner or scratch lightly with blade.
Add flux and solder ,try to touch the pins only with soldering Iron to prevent damage to plastic pack.
File the soldering Iron tip to make it thin ..heat just enough to melt the solder..otherwise the tip will bend as it is filed .
now hold the chip in tweezers and place according to the pin 1 dot .
Step 3: Examine Under Light
Why ? this angle will let the copper part on the sides of the QFN and PCB pads visible together .
Carefully align the IC till two adjoining corner pins match with pads.
See that IC is placed in such a way that pads are a little visible.You will touch the pads to attach the IC.
Step 4: Tape It
Remember: taping can misalign the IC a little , recheck and remove the tape if needed .
Make sure that final taped position is correct.
Step 5: Anchor It and Final Solder
Corner two pins you solder first . see the position of the I C , adjust a little
by melting the solder if needed.
After this you can remove the tape,now the IC is secured .
Just solder the other pins by touching the pads . add a little flux time to time .
Tip : Dont heat the chip continuously, do it for 5 -6 sec and stop.
Let it cool ... then gain do other pins .
Refer this instructable for that process: https://www.instructables.com/id/hand-soldering-teeny-tiny-chips!/