Step 8: Soldering the Components
To begin I needed to learn how to solder surface mount components. I've done a fair amount of standard sized soldering, but hadn't touched surface mount since school (a long time ago) and that was with one of those fancy air tip soldering irons. Watching this incredibly well-done tutorial on surface mount soldering by CuriousInventor gave me the instructions and confidence I needed to work on this project.
For each component I first placed a small drop of flux on each of the points of the board to be soldered. The flux I had on hand was in a small tub, not a tube with an applicator, so I needed to dip a paper clip in the flux and then dab it onto the pads. I then held the part to be soldered in place with a pair of tweezers, loaded the iron's tip with a droplet of solder, and quickly touched the iron to one of the components leads. That first soldered lead held the component in place and made soldering the other leads much easier.
To give myself more working room I soldered the parts starting with the smallest resistors and moved up to the larger ICs and LEDs. The LEDs were soldered onto some leftover leads I had cut earlier, and these leads were then soldered to the board. My first attempt at doing this resulted in the wire lead becoming hot enough to desolder the LED from the wire. It was necessary to use a small alligator clip as a heat sink to prevent this. The leads were then bent back to fit behind the CD lens eyes (and fine tuned in a later step).
While soldering the PicAxe08M2 I made sure to not get the chip too hot. I soldered one pin and then waited a good two minutes before soldering the next. Truth be told I likely could have just used a socket, but I was unsure if there would be enough room in the shell for one.
The jumper that I had intended to use to switch from the eye LEDs to the programming pin ended up being to big to fit in the shell. To slim the jumper down I removed all of the plastic leaving just the contacts. I also needed to solder the jumper pins to the board at an angle to make room for the jumper.
The most difficult part of the soldering was the micro-usb connector. The pins on this part are very close together and I just couldn't get my iron in there without bridging the solder across them. After a half dozen failed attempts at doing so, I finally took the advice from the above linked video and used a stripped piece of braided wire as an improvised soldering wick to soak up the extra solder from the pins. Afterwords I made sure to test all the pins with a multimeter to ensure that they were not bridged in anyway.
The male micro-usb connectors have spring loaded pins that lock into the female socket. These pins are strong enough that considerable force is needed to disconnect the two. The female connector has multiple ground solder pads connected to it's metal body. Securely soldering these pads prevents the connector from being ripped from the PCB when the two are separated.
After a majority of the components had been soldered to the board, it was scrubbed down with a toothbrush and denatured alcohol. This removed most of the ugly flux and dust that accumulated on the board leaving it nice and shiny.
After this cleaning, the IR sensor and piezo speaker were added. To allow it to extend through the top of the shell, the leads of the IR sensor needed to be bent around the peizo speaker.
The motors were then soldered to the board and secured with hot glue.