One common skill in project making is soldering wires together. Splicing wires together is never safe enough especially when dealing with smaller gauge wires, which is the common scenario with building microcontroller projects. Soldering wires after splicing ensures that the connection will stay strong.
If using stranded wires, it is necessary to twist the stripped end together to make them more orderly. This will also make the stripped wire easier to solder later on. Solid wires, obviously, need only to be tinned.
Next, dip the wire into a soldering flux paste for better solder flow. Copper wires will never have issues with solder flow but there are other wires which makes it hard for solder to cling to.
Tinning the Wire
Carefully apply solder to the wire. Remember to touch the soldering iron to the wire and then apply the soldering lead to the wire. Do not allow the lead to touch the iron directly! Also, make sure you apply just enough solder that the original shape of the wire is still visible. You may apply solder up to very near the insulation of the wire.
Next, after tinning the wires to be connected, splice them for a stronger mechanical hold. There are a number of splicing techniques but I prefer the western union splice:
While the western union splice is generally for solid wires, you can also use it for tinned stranded wires. Make sure that the tip of the wires are pressed tightly for a cleaner look.
Apply Solder to the Splice
Finally, apply the soldering iron to the spliced wires and the solder from each wire previously applied should melt and join to form a strong bond. You may add a small amount of solder to fill in holes if there are.
You may then cover the connection with electrical tape or heat shrink tubing for protection.