Last night, I gathered all the parts for the Weather Station and did some assembly. Installing a few dozen parts by hand, on a 12.5cm² PCB is an intricate process.
I start out with a huge printout of the PCB layout, an unpopulated PCB, and this excellent anti-static parts tray from iFixit. All the big and identifiable parts go here. When I’m feeling more energetic, I sometimes print out a specially-formatted parts list that goes under the tray, but I didn’t do that this time. Just out of frame, there’s a stack of bags with hundreds of tiny surface-mount capacitors, resistors and inductors. Since they’re not easily-identifiable, I keep them in labelled bags and deal with one at a time.
Next, I align the solder paste stencil over the bare PCB and squeegee the paste onto the board.
That paste is made out of microscopic balls of lead-free solder, held together with a sticky material called flux. As you can see in the photo above, it’s not a perfect application of paste, but the reflow process is somewhat forgiving: the surface tension of molten solder helps to settle the parts into better alignment.
About a half-hour with curved ESD-safe tweezers, and the board is fully-populated. At this point though, all the parts are simply resting atop the sticky paste.
Into the oven!
This is a modified toaster oven, that I use for the sole purpose of baking electronics. There’s my new board, ready to get baked!
I really did have far too much fun building this toaster… I ripped out the existing thermostat and timer, and installed my own completely custom control panel and temperature control circuitry. And it does a pretty decent job of following the time/temperature curve that I programmed into it!
A few minutes later, and after it’s all cooled down, I’ve got a completed board!