Page 409 - Hacking Roomba

390 Appendix A — Soldering and Safety Basics

Safety Considerations

Building circuits uses dangerous chemicals and devices that can burn or otherwise harm you.

Know at all times where your soldering iron is. The tip gets up to 800ºF and can burn
your skin so fast it cauterizes and deadens nerve endings so you won’t feel it at first.
Never touch the tip of the soldering iron unless you know it’s cool. One way to check its
temperature is to hold your hand above its tip, several inches away. If you can still feel
warmth, it’s too hot to touch. Even so, once the air above the tip feels cool, you probably
should still give it a few more minutes to cool off. It is better to be a little patient than to
end up with an unnecessary scar.
Wear safety goggles. Molten solder can splash, especially when coming into contact with
cool things like large metal surfaces or the cleaning sponge.
Keep your work area well ventilated. The rosin flux and other fumes from soldering are
not meant to be inhaled.
Wash your hands thoroughly after handling solder and any components. Lead is toxic
with prolonged exposure. Many components have lead on them, but also a lot of them
are just dirty.
Never solder on a powered circuit. The soldering iron is grounded for static safety rea-
sons, but that presents a shock hazard if the circuit is connected. Always disconnect all
power before soldering.

You will burn your fingers a little now and again. It’s part of the initiation of learning how to
solder. Sometimes you have to hold a part in place with your fingers while you solder it. But
try to minimize burning yourself by using the proper tools and procedures as described in this
appendix.

Soldering Components

Soldering two parts together not only creates a connection that can conduct electricity; it also
makes a mechanical bond that can be quite strong when done correctly.
To solder two things together, you must first tin each part with a thin layer of solder. Tinning
is the process of applying a thin layer of solder to a metal part. The part turns silver colored
where the solder has been applied but otherwise shouldn’t look different than before. That is, it
shouldn’t be blobby with solder.
Solder naturally likes flowing along metal, so tinning parts isn’t very hard. Many components
already come pre-tinned to make them easier to solder. Usually you’ll want to add just a little
more solder when making solder joints.
The recipe used when soldering is:

1. Tin the first piece.
2. Tin the second piece.