I’ve been spending a decent bit of my free time lately on my binary watch project. I have a full writeup that I added to the projects section (which goes into more detail about the hardware and software used, and contains information about my github and storefront), but I figured I’d also do a post on the production flow I’ve been using, since I think that’s kind of cool (thus reaffirming that I am an embedded systems nerd : )
To start with, I made the conscious decision at the design phase of the project to use a QFN package for the microcontroller in order to save space and force myself to improve my soldering skills and tools. This package has two big hurdles to overcome. For one, it does not have leads extending from the package like I’m used to with, say, a TSSOP part.
Instead, the exterior of the package has exposed pieces of metal on the outside and underside of the package that the solder must adhere to. The second big hurdle is that the package has a very large ground pad in the center. Since the ground pad is not exposed, it is nearly impossible to get solder to flow on it without using either a hot air rework station or a reflow oven.
For more Details: Binary Watch Production