Circuit boards are in

I got the printed circuit boards (PCBs, in electronics speak) mid-week for my production prototypes, and finally soldered everything yesterday.

Here is the printed circuit board as I'm populating it, the microcontroller (brains of the operation) is about to be soldered in.

Here is the printed circuit board as I’m populating it, the microcontroller (brains of the operation) is about to be soldered in.

For the prototypes, I picked the bigger packages of components because I would be soldering this board by hand. Eventually, the production version will use smaller parts to keep the board size down, and they’ll be machine-assembled so hand-soldering won’t be a concern. However, the charger IC (integrated circuit, that’s a chip) I had my sights on only comes in the minute WSON package. I kid you not, that acronym stands for Very Very Thin Small Outline No Lead Package. That’s no typo, there are two Verys in the W of that acronym. The gap between pins on a WSON package is 0.25mm (for reference, the gap between pins on the microcontroller is 3.75 times wider) plus the pins don’t extend beyond the chip body… and the anticipated difficulties soldering something so small by hand is why I ordered a couple of extras. I’ll admit that’s a lesson I learned the hard way; a few years ago I worked on a project and ordered my normal extras rate for a WSON part, then and had to order a few more later. You can see this tiny charger IC in the next picture, to the left of the USB connection at the bottom left side of the photo.

After a few attempts at soldering the charger IC that didn’t work out, I managed to populate some working boards. Here you can see an orange light on the finished board, as it charges a lithium polymer cell from the micro USB port on the board. That light changes to green when charging is done.

The assembled PCB while charging a LiPo cell; the orange light indicates charging is not complete. Sparrowscope PCB logo

One of my favorite parts of this circuit board isn’t even functional—the other side has the Sparrowscope logo on the copper layer. 99% of Sparrowscope owners will never see that on their Sparrowscope, but I like that it’s there.