How to solder, is probably one of the first questions a budding electronics engineer might ask, but there is no need to be shy, we all have to learn! While soldering isn't very difficult there are few things to remember when soldering:
Soldering irons are very hot and molten solder will burn you, your clothing and any surfaces it may land on. Never touch the tip of the iron. Wear safety glasses and protect your table top with a protective mat, preferably something that is heat resistant. Be extremely careful not to overload the tip to the point there are beads of solder ready to flick of at any second. Always return the soldering iron to its stand when you are not using it. Do not put it down on your table top, or balance it anywhere while not in use.
Its always best practice to wash your hands after soldering as some solders contain Lead and flux which are toxic.
Now we have that out of the way we can move on to the process of soldering a joint.
Before you start to solder
Place the soldering iron in its stand and plug in the iron and allow to heat up. This normally takes a few minutes so while you wait, dampen your soldering sponge.
When the soldering iron is hot, make sure you clean the tip on the damp sponge before you start to solder.
Once you have cleaned the tip, apply a small amount of solder to the clean tip, this is called tinning, it will help the heat transfer from the iron to the joint easier.
Polarity and reducing heat in components
When soldering, some components may have a polarity or a specific lead out. Make sure that the component is in the correct position before soldering. Some components may be damaged by excessive heat, so using a heatsink when soldering them is a good idea. Some components may also require you to follow anti-static procedures.
You are now ready to make that first solder joint on your new electronic project!
Try to hold the soldering iron similar to how you would hold a pen or a probe, it will help you accurately pin point the joint to be soldered.
Hold the tip of the iron to the joint, making sure that you heat both the board (track if using stripboard or solder pad using a PCB)
Apply the solder to the joint (not the iron), use as little as possible. Remove the solder and then the iron, so that the free solder isn't left attached to the joint. The joint should form a triangular/cone shaped bead around the lead. The solder should be shiny. See diagram below.
Check the soldered joint to ensure that the solder is shiny and has formed a cone shaped bead as in the diagram above. Dry joints are usually dull and more of a round or irregular bead shape.
Sometimes you may realise that you need to remove a soldered joint. You can do this by using a "solder sucker" desoldering pump or solder braid.
The "solder sucker" removes solder by sucking it away from the joint allowing you to remove the component. Simply prime the pump plunger, apply heat to the joint, apply the tip of the desolder pump and press the button to suck the excess solder away. Solder braid works by absorbing the excess solder simply heat the braid and joint and it will absorb the solder.
What solder to use
Solder comes in various thicknesses and also chemical compositions. Solder can be lead 60/40 or lead free alloys which include precious metals such as silver. The solder usually has a flux core to help the solder flow into the joint.
Lead solder has a slightly lower melting point (~200C) than lead free solder (~220C) the thickness of solder depends on the application. Standard electronics work would generally require 0.6-0.8mm thickness solder. Larger joints may require 1.2mm+. Thinner diameter solder will melt more quickly, reducing the chance of damaging components with heat.
Tinning is the process of adding a little solder to the leads of the components or wires before soldering them. It is sometimes necessary to do this to help make the soldered joint more quickly and cleanly. Tinning a component before soldering wires to it is always beneficial.