How to solder QFN SMT package chip by hand (video)
QFN pitch could be as small as 0.5mm. To make the things worse, there are no leads coming out of the package. The only externally accessible contacts are on the sides, which seem to be the last hope to solder by hand.
But impossible is nothing! I’ll show you with photos and video how I am able to manually solder a 64-pin QFN chip.
1. PCB footprint design tips
Design the pads slightly bigger than standard as you might need some extra room for the soldering iron to access. I extended the pads about 0.71mm out of the package and it is enough for the soldering tip to access.
2. Principles behind QFN soldering
Bear in mind that, when dealing with small packages like QFN, you are not going to solder pin by pin simply because it is not quite doable. The way it works is to make use of the flux and let the molten solder naturally flow onto the chip leads and PCB pads. Solder’s surface tension will automatically separate itself from building bridges between pins. In some cases, however, too much solder is applied to so the bridge occurs, simply use a clean soldering tip or copper wick to remove the extra solder.
Here is the comparison between before and after the soldering.
Thanx! Which flux (is it critical ?) and how do you clean it ?
I highly rated this, because more and more chips come in QFN while ‘SOP/SO versions get obsoletted. I was happy to find your site, because now I have hope to be able to solder a 5×5 mm QFN-32 chip.
Note: You didn’t talk about the ground plane. In my QFN chip, there isn’t a “GND” pin. So the GND will be soldered by making a hole via the board, big enough to allow solder to create a “via” connection to the ground on the back side of the PCB.
You are right, more and more chips are becoming less and less hand-solder-able. QFN package still can be manually soldered, however, the bottom GND pad is a problem. I didn’t care too much about leave it as it is usually a redundant ground pin. That’s why I built the “Reflow oven“. Your “via” idea might also work.