(next day edit for coherence)

Boards came in today, so I had to get the reflow toaster out.

In the toaster during heat ramp up. I'm using only a thermocouple thermometer and a clock. No fancy profile controllers here.

So far, so good: the ESP-12F works well in 4-bit mode. The switcher tolerates feeding the Pi from the Pi microUSB input while not operating, and the shutdown input does what it's supposed to.

The reflow worked better than expected. I was concerned about the thermal vias under the switcher chip. They're necessary to transfer heat away from the chip and into the ground plane on the back side. But without special treatment during board manufacture (tenting, plugging, blind vias) they can wick the solder out the back and prevent the chip from making good thermal contact. OSHPark and other low cost board houses don't do any of those. So I increased the amount of paste on the pad to compensate. But that can have the opposite effect if the vias don't suck up enough, and the center pad will float the chip too high for the other contacts to solder to their pads. Fortunately none of that happened as far as I can tell without running it through an x-ray.

Most importantly, no smoke was emitted.

The switcher is happy to power a Pi A+ plus a bit of extra load on 3.6v worth of NiMH cells. Next step is load testing the switcher.