Since many of the attendees at our first gathering are students and beginners of Arduino, I felt that I should share my experience on tools and supplies in order to make your experience with Arduino the best you can. I remember my bad experience using a soldering iron in college and how that negatively affected me over electronics for years. So I wanted to talk about soldering iron and solder. If you are considering using solder-less breadboards and jumper wires, you will still have to solder some headers to your breakout boards (maybe that Bluetooth module), and knowing that soldering is no magic helps a lot. I remember one time I was visiting Bill’s art class and one student casually mentioned that he was afraid of soldering so he was not able to do certain things. That was me, only that I got over it already.

So here it goes:

Why solder if you can use jumper wires?

Soldering is the action of connecting two metal pieces with a third metal. The connection, or junction, is very difficult to break and provides best electrical contact against noise and accidental/intermittent disconnection.

The first two metals could be two wire leads, a resistor leg and a copper pad (hole) on a circuit board, or a pin of an integrated circuit (IC) and its copper pad on a printed circuit board. The third metal is solder. It is usually an alloy. You melt the solder into liquid, have it wet the first two metals, then let physics take its course. The solder solidifies and connects the first two metals.

How soldering works?

This process requires two main things to happen:

1. The two metal parts need to be hot, hot enough to melt solder themselves. You don’t want the metals to be cold when you add solder to them. Physics tells you that the hot solder will try to minimize its surface area (reads energy) with the cold metal and ball up, most likely making a very weak junction. When was the last time you had a “kisses” chocolate drop? That is the shape of bad soldering job, because the same process of hot liquid contacting cold surface makes it, but enjoy your chocolate (I mean physics I just stuffed in it).
2. The two metal parts need to be clean, with minimal grease and oxidation. A flux, a chemical, cleans the metal surfaces and also makes wetting easier. This flex is usually inside soldering wires. It evaporates soon after soldering is done. You usually don’t need to add more flux but sometimes when you want to reflow (reheat solder so it flows to the right places or takes right shapes) a few bad solder junctions, adding some flux helps removing the “old solder” feeling and makes the solder easy to flow again.

How do I solder?

1. You will need a decent soldering iron that is temperature-regulated to not get too hot at times to splat solder or too cold at other times and becomes a jabbing device. A good temperature-regulated iron can be had for around 100USD. I have the following Hakko brand iron in my development office. It is pretty good for all sorts of work, even surface-mount soldering, in case you ECE student wants to know about it. https://www.adafruit.com/products/1204
2. You need some decent solder. There are tons of different solders but I want to focus your attention at three things: composition, diameter, and core. For composition, I recommend 60/40 lead solder. Your environmentalist self may be blaming you for even thinking of polluting our mother earth with poisonous lead?! But lead makes the best entry-level solder. Once you master your basic skills and acquire some extra fund, go ahead and get lead-free. Th 60/40 is a typical 60% Tin 40% Lead composition. It melts at a lower temperature than lead-free solder and easily wets surfaces and makes very shiny junctions if you did your job right. Or it will not look good at all so you can easily tell if you did a good job. Lead-free solder only has a shiny surface while in liquid. When it solidifies, even a good junction turns dull in the matter of a second. Checking quality will be difficult. Regarding diameter, you are better off with 0.03inch diameter solder than anything too thick (hard to control amount of solder) or too thin (keeps feeding solder to one junction is tiring). This 0.02″ diameter lead solder looks pretty good: https://www.adafruit.com/products/1886 The last thing is the core. NEVER EVER purchase acid core solder!!! They are for plumbing and will corrode your electronics!!! Most other cores are fine. Some are “no-clean” meaning you can leave the residue on the board and it will not bother the board. Some are “water-clean” meaning that you should wash the board to remove residue after soldering. Rosin core should be fine too. It is a good idea to clean the board with some alcohol after soldering, if it is not because of the better looks.
3. Press your iron tip against the two metals and wait patiently for up to 10 seconds. Your first few junctions may take longer to heat up and last few junctions are taking less time since the board is probably hotter by now.
4. Bring the solder in the opposite side of the two metal and press it against the metal, not the iron. You could “cheat” a bit by temporarily touch the solder to the iron and then move back when it starts to melt.
5. Have the iron against the metals at all time when feeding more solder wire to the junction. I always see over application of solder than under application of it. This tells you that don’t use so much solder. If your iron tip already has too much old solder, wipe it with metal wool or water sponge. Have a shiny tip before doing your next junction.
6. Once enough solder is on the junction, move the solder wire away and then remove the iron, with a wiping action that takes the tip of the iron from the junction along the metal. Don’t do it too fast as you will create spikes.
7. Always check your connections. A good junction looks shiny. It is the result of the concave solder surface making a real image of the room light, a mini light. A bad junction looks not so shiny. It is the result of convex (balled-up) solder surface having no capability to form real image of your room light of any kind.

Any last words?

Check your parts before soldering! Don’t just go ahead and solder. If you solder an IC backwards, it is practically impossible to take it out. You may try de-soldering iron in conjunction with solder bread and solder sucker but it is going to be a bad day for you!

I’ll probably make some videos and pictures when I have more time. Find a kisses photo with permisson as well. Send me one?