A soldering iron is one of the most used tools by someone doing electronics. It consists of a heating element that melts a metal alloy, called solder, at a lower temperature of the parts you are sticking together. The solder conducts electricity and as such connects two parts together. This can be a component you solder to a printed circuit board or a wire you solder into a connector.
A solder joint is a mechanical connection between parts.
There are several types of soldering irons
- Simple heating iron without any regulation. these irons are the cheapest kind.
- Temperature controlled iron. This is the recommended type.
- Soldering gun. This heats up very fast to a very high temperature. It's hardly ever used in electronics
Power and mass
A typical electronics soldering iron has a power of 25W to 40W. If you get a type without a temperature setting, do go for the lower wattage or you risk burning components or PCB traces. A higher wattage iron will heat up faster but make is harder to control. For smaller work you can get soldering irons as low as 15W. This is too small for a beginner.
On the upper range you can get soldering irons of around 150W. These are certainly not recommended for regular electronics work but are used for soldering copper pipes or gutters. Due to the huge heat loss from the large metal parts, you need an iron that can very quickly heat up a bigger mass locally. The mass of the iron also helps in heating up bigger bits like batteries. I use an 80W heavy iron to solder batteries. This allows me to locally get the battery connection up to a soldering temperature without heating up the electrolyte inside.
I recommend using solder with a resin core. This resin makes the melted solder flow better and avoid oxidation which makes it easier to get the parts to stick together properly. For electronics use get resin core solder with a thickness of 0.5 to 0.3mm diameter. For soldering wires that need to carry some current you can use solder with a diameter of 1mm. Thicker solder is not recommended as you will not have any control over the amount of solder that is applied and pretty quickly create solder blobs.
The solder on a soldering iron will oxidase on the tip when it's hot. You'll see that the tip loses its shine when this happens. This oxidation dos not flow very well nor does it conduct electricity as well as clean solder. On top of that the resin has long been burned off which makes the solder flow even worse.
So it's pretty clear that cleaning the tip of the soldering iron prior to soldering is absolutely necessary. Most soldering iron stands come with a little sponge that you have to wet before you start soldering. Just wipe the tip of the soldering iron over the top every time you pick it up to solder tomething
As an alternative you cab use a brass wire sponge in a container. The brass attracts the solder very easily so just sticking the tip of the iron in the brass wire sponge is enough to get the tip nice and clean. Personally I like to use this way of cleaning the tip as it's easy and quick.
Here's a good video showing the beginnings of soldering