I've been having some trouble with the first Megsy / Teensy 3.2 / Teensy Audio Board stack, and thought perhaps it would be a good time to try to solder together a 2nd Megsy board.

Originally, I had intended to try to hand apply solder paste, and apply heat through the vias with my soldering iron. I don't have a mask for the solder paste though, and I was worried about the paste squishing out and bridging connections when I squish the two boards together. So I hadn't tried it yet, even though I had obtained the solder paste some months ago.

I went to a surface mount soldering lesson a few weeks ago, and they showed me how hand soldering is done when the part has a thermal pad on the bottom of the board. It was not too dissimilar to what I had considered for Megsy! They were heating the vias, but they were also using flux and regular solder and then just letting the solder flow through the vias to where it needs to go. Evidently, if you use flux, solder will flow like that.

I had never used flux before, despite Design Lab Resident Engineer Dan's exhortation to "make it look like somebody sneezed all over the board". But having seen it in action, it seemed like it was worth a try.

I bought a flux pen at Fry's for about $10, which was probably too much, but who wants to wait? Evidently me, because I didn't touch it for another 3 days...

When I finally got my courage back up, I put flux on both sides of the megsy board, and on the bottom of the Teensy. I used pin headers to line up the holes and started applying solder and heat.

I watched carefully. It seemed like the solder would bubble for awhile and settle, so I would hold the iron on each pin until the solder stopped bubbling, hoping that was enough time for good flow. A check on the top of the board for some holes that went all the way through shows that the solder did indeed go through the holes on BOTH boards! Bravo!

We'll just have to hope it made good connections to the pads on the bottom of the board. Or rather, I'll eventually have to wire up test circuits for that.

For the pin headers, the plastic spacer is on the top for the Teensy Audio Board to rest on, which makes it hard to get solder through, so I did the same thing with those. I was worried that the solder wouldn't flow well around the pins, but it seemed to flow fine.

I'll have to do some extensive tests to make sure everything works, but so far I've managed to upload software to it (blink!) and the reset button on the Megsy board does indeed trigger the reset line that is only accessible via a very small pad on the bottom of the board, so it looks good for my poor man's BGA connections working!

So far so good! I'll update this after I've done further tests.