What Is Soldering?
A soldering iron is a tool with a metal tip that gets really hot. We’re talking like 800 degree Fahrenheit, though you can adjust the temperature on a good iron.Its job is to transfer heat to things like wires, transistor leads, and pads on PCBs. After the appropriate areas are heated properly, solder is applied. If you plan on soldering, then you’re better off spending $30-$40 on a 20-30 Watt iron instead of on a cheap one. You’ll get a longer-lasting tool that will work for a much wider variety of applications and you’ll get proper heat control to boot. There are also soldering guns available, but you should only use these when repairing thick cables and never on PCBs, as the tips have a live voltage running through them that can damage sensitive electronics.
Solder is a thin tube, usually rolled in spools, made of various metal alloys. Its job is to hold the individual components together. The individual components and their quantities can vary, but for computer electronics, you’re usually looking at a 60% tin and 40% lead. Lead-free solder is also available, though it has higher melting temperatures and less “wettability,” meaning you may need a better soldering iron to use it and removing it can be more tedious. Lead-free solder is better for the environment and has other benefits, and they function more or less the same way.
The inside of the tube is filled with “flux,” a substance that gets rid of oxidation and helps clean the surfaces involved in the fusing process. For electronic use, you want rosin-core/rosin-flux solder. Acid-flux is used in plumbing and the acid can damage the sensitive components on PCBs.
Safety First!
Many who’ve never used a soldering iron are afraid of damaging equipment, but more important is the danger to yourself! Soldering irons get really hot (think, and solder itself is molten metal. Be sure to wear safety glasses, keep loose clothing and hair out of the way, and be careful with your fingers. Better still, use protective gloves. Solder can contain lead, so be sure to wash your hands thoroughly after handling it. It’s also really important to work in a well-ventilated area because the fumes from the rosin can cause damage to your lungs when inhaled. Honestly, it’s more common sense and preparation than anything. Just take proper precautions and you’ll be fine.
In order to conduct heat properly, your soldering iron needs to be free of any old solder. After being exposed to air, it oxidizes and thus insulates against heat. We want heat to conduct so that we can apply everything quickly and efficiently. A dirty tip means that you’ll have to hold the iron on longer and risk heat damage to the PCB, and nobody wants that. Keep a wet sponge handy, and after the soldering iron is fully heated, softly scrape it against the sponge to remove old solder. The tip should be nice and shiny, or at least very close to it.
Next, we’re going to “tin” the tip. This will protect the tip and allow heat to conduct better via the presence of new solder. On the hot iron, carefully apply a small amount of fresh solder and coat the tip. It should still be shiny if you’ve done it right. As soon as you tin the tip you should start soldering your components together. After every few joins, clean and re-tin, and again before putting your iron away into storage. This will really help increase the longevity of your tool. A good soldering iron should easily last years this way.
Joining Parts
Now, this is really important. Pull away the solder first, and continue holding the iron for another second. This allows the solder to continue to melt and pool, forming a good joint. Then, you can remove the iron. The total process shouldn’t take more than 5 seconds, and usually you’re aiming for 3-4
Wait a few seconds and don’t disturb the solder. It cools very quickly, but moving or blowing on the joint will cause it to deteriorate. A bad solder connection will look really oxidized, overly dull, and grainy. It also sort of looks like a ball of solder formed on the area. A good connection should be smooth and uniform, and its sides will be concave. It won’t look like a raised ball, it’ll look flat.
When removing a connection or undoing a mistake, you can often resolder over the original and add a touch of new solder. If you want to take the extra step and do it right, you can remove the old solder completely and start with a fresh work area. There are two tools you can use for this, a vacuum-based “solder sucker,” or a solder wick.
A solder sucker is essentially a tiny hand-held syringe-like pump. It creates and uses vacuum pressure to suck solder off of whatever it’s on. It’s a great tool to have and works well.
A solder wick is woven copper which the old solder bonds to. It’s more expensive and it’s expendable, so I usually don’t recommend it. Some jobs, however, will greatly benefit from the clean finishing touches that a solder wick provides. Both tools have their strong points, and odds are that in your soldering career you’ll need to use one or the other specifically from time to time. Having a clean working area is really important, as it provides the best results and minimizes risk of damage.
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