Quick QFN40 Soldering Tutorial
As a small hardware company, we’ve benefited immensely from the myriad of tutorials others have made freely available online. In the spirit of giving back, here’s a really quick demo of how to place a 0.5mm pitch QFN40. Because of its very fine pitch and lack of leads, this can be an intimidating package to solder. With practice it becomes much easier.
Things I failed to mention in the video:
- My iron is a Weller WES51 with a long conical tip
- In this demo it was set to 700F
- My flux is MG Chemicals 8341
- My solder is a Kester Rosin Core 63/37 Leaded solder
- You can do this without a microscope, but for the sake of your back and your eyes I recommend a microscope with 5x-10x magnification for this sort of fine-pitch work.
Questions? Comments? Let us know!
I’m glad that you know what’s right, bad that we are doomed for leadfree Mooshimeters
A key thing not mentioned is making sure the QFN PCB footprint used extends out far enough to allow access for manual drag soldering. Many default (e.g. IPC compliant) footprints supplied with PCB software or component libraries aren’t suitable for the drag soldering technique, or have several options for PCB component density. Another tip is to use kapton tape to shield nearby pads from excess solder during this process, although some solder wick makes a pretty quick job of that.
You’re totally right, thanks. On these footprints the pads extend about 15mil past the edge of the part. That’s pretty close to the minimum to use a drag soldering technique.
Any tips if I’ve got shaky hands?
Make sure you have solid places to rest your wrists. If you have your elbows on the table and your wrists are floating you will tremor much more than if your wrists are firmly planted on the work surface.
James, you’re right about resting your wrist during soldering to avoid tremor. I just wished they’d make soldering irons with shorter nose lengths for just that reason.