Aha, now we’re getting somewhere:
Almost perfect reflow this time – only had to fix 2 solder bridges on the rightmost FTDI chip, then add the USB connector and wire antenna. All four worked right away!
The trick is to press harder on the stencil at the end, so that a truly thin layer of paste remains when lifting it off. It was a bit too thin in some places in fact, so I had to dab a bit of extra paste on a few pads.
This stencil thing is indeed a huge time-saver over applying paste with a syringe to each individual dot. It’s not just the amount of work, it’s also the type of work: keeping a steady hand while doing all those 100′ish dots per board was extremely tedious.
The total time spent on assembling these four boards was 1:30 hours – not stellar, but ok.
Four more boards done!