Hi Reader,

Just wanted to share some pictures of the assembly process for the RevF prototypes.

All previous revisions have been assembled by hand with either a soldering iron or a paste dispenser.  I swear by my Weller WES51 iron, but my paste dispenser tends to make a mess of all the finer pitch ICs and I just drag solder them.  Recently I met Jeff of Tempo Automation, who are building the dream of desktop pick-and-place machines (real ones, with vision systems!).  Jeff let me use their laser cutter and showed me some assembly tricks that made these boards come together much faster than the previous revisions.

I modified the solder paste layers of the RevF design for the laser cutter (this involved bringing in all the pads by about 50 microns to compensate for the laser kerf) and Jeff cut them out using his disposable stencil medium of choice – cardstock.

The cardstock actually holds good images and I was able to get good paste application through it after a few tries.  The 0.5mm parts didn’t have perfect paste dispensation, but it was good enough to continue.

Component placement was still all done by hand and was by far the slowest part of the process.  After placement and reflow the boards look like this:

If you look closely you’ll see there are some bridges between the pins of the ICs and the smaller packages.  A good once over with the iron fixes those right up.  Then I mounted all the through hole components by hand.

After that, it’s time for power up.  This is easily the single most nerve racking part of bringing up a new board.  Many design mistakes will manifest as an acrid smoke when you power up the board. But that didn’t happen here, the boards connected to the debugger and accepted firmware, no problem. All hail the blinky light.

Now to make the firmware and app modifications to support the new hardware, as well as test the stretch goal features that were added in this revision.  Thanks for reading.