The tiny AEMLIC board comes with simple plated castellations (metal soldering points on the side of a board), five on each side. I have soldered headers onto multiple Raspberry Pi Picos using the standard through-hole approach, but never directly to thin castellations. I searched the internet including youtube, but could not find any tips or tutorials on how to do this. This is not a critique of the boards. I should have asked Jasper Sikken how he does it. Perhaps he or someone else will offer their advice as a comment? Anyway, here's what I did.

I have an up-to-date good-quality soldering station (Hakko FX-888D). My very old tin/lead solder had been working well, but perhaps it was part of the problem? I placed the two AEMLIC headers into a small breadboard, placed the AEMLIC board on top, and proceeded to solder at 750°F (398.9°C) which is what I've been using. The result looked OK.

I then made several mistakes connecting the board to a solar cell that I had, to the LIC, and to a small load. Nothing worked. I'll describe these mistakes in a separate log. I contacted Jasper Sikken through Tindie. He promptly suggested that I had probably fried the board because of the mistakes I had made (a great learning opportunity!), and kindly offered to send me a new board at a much discounted price.

While waiting for the new board, I thought carefully about the several tasks that I had worked through, starting with the soldering. Through a magnifying glass and the old brass microscope I got as a Christmas present when I was 10, I concluded that my "soldered pins" looked very sparse. Was there really any solder on them?

I had tried to do some quick continuity testing after soldering, but the thickness of the tips of the leads on my just-purchased ExTech 355 multimeter make it difficult to know where I was actually touching. I cut a piece of thin solid copper wire and placed it between the plastic covering and the tip of the red lead. With much finer control, and using the Continuity setting of the multimeter, I decided that most of the ten pins did not actually contact the castellations on the board.

It turns out there is still an electronics store in my city. I bought fresh 60/40 0.031" solder, a smaller soldering iron tip, and a container of 99.9% isopropyl alcohol. The 70% isopropyl alcohol I had bought before at the local pharmacy was unable to remove the flux, which then prevented me from getting any sort of continuity reading on most of the pins.

I was ready to rework the solder. I decided not to remove the existing old solder, because it had worked well on other projects. With the iron at 750°F (398.9°C), I found that the new solder I applied, just came off when I removed the iron, so I still had bare pins with no continuity. I tried 700°F (371.1°C), and it worked! I experimented with 650°F (343.3°C), which also worked, but the result had tiny peaked "hats" over each solder.

I then washed off all the flux with the 99.9% isopropyl alcohol using a Q-tip and a stiff hog-hair brush. It all looked great and shiny through my magnifying glass. This time, the continuity testing worked perfectly and decisively. Each castellation was connected to its corresponding pin. Jasper had mentioned that all four GND are connected inside the board. I was able to confirm this using the multimeter continuity setting.

Summary:        Solder at the right temperature

TO DO
 - include some pictures