The DFN Soldering

The Sensirion STS3x temperature sensor is a pretty small component, with a footprint of 2.5mm x 2.5mm, so needless to say it needed to be placed on a breakout board for use. I ordered a standard SMD breakout adapter that provides accurate pin spacing for breadboard use to make my breakout board. With no reflow oven and just a single component to mount, I decided to use some solder paste and a standard heat gun to surface mount the device. This was actually my first time DFN soldering and it only took me a few tries to get it right. It was easier than I thought it would be.

The solder paste should be spread on each of the land terminals of the breakout board, as well the thermal pad in the center. The pads are very small and the process will probably get a little sloppy, but there's not much else you can do with the tools at hand. Fortunately enough, as you apply heat, the solder naturally becomes smooth and neat and should take to each of the individual terminals. Place the sensor chip in the center of the breakout board. Apply heat until you see the solder become molten.