Nuts and Volts - February 2009

onto the leads you want to solder, you first rub the tip across the wet sponge to clean it. Then, you melt a little solder onto the tip to make it easier to transfer heat to the items being soldered.

You will also need a pair of cutters to trim off the excess leads after you have soldered them. This is necessary whether you are soldering components to a printed circuit board or twisting them together to make a connection. When you clip the leads, wear goggles to protect your eyes as the leads sometimes fly away very quickly when cut. You may want to point the lead being clipped down directly into a wastebasket while clipping it, both to protect your eyes and to catch the clipped lead.

You should wear long pants while soldering. Since you are almost always sitting while soldering, it is not uncommon for molten solder to accidentally drip off the tip of the soldering iron when you pull it away from the circuit. Sometimes the molten solder drips onto the table where you are working, but it could drip onto your legs. It is very hot and will easily burn you if it falls on your bare skin.

FIGURE 2. Here is everything you need to solder an electronic project.

Soldering To A PCB

If you are soldering components to a printed circuit board (PCB), it is important that the copper traces on it are clean. Copper will slowly oxidize when exposed to air (actually, the pollutants that are in air). This thin layer of oxidation will make it harder for the solder to adhere to the copper. It is a good idea to gently rub the traces with steel wool or fine sandpaper before soldering anything to them. This removes the layer of oxidation and makes tiny scratches in the copper, which also increases its surface area and gives the solder more places to attach. After you have cleaned the traces, be sure not to touch them with your fingers. Hold the PCB by its edges as the oil on your fingers will deposit on the copper and begin oxidizing it. If you wait long enough, you will eventually see the pattern of your fingerprint etched in the copper!

It is usually necessary to solder wires to a PCB to carry power to the board and signals to the off-board

components such as switches and speakers. If the wire is stranded, you may want to tin the wire before soldering it to the board. Tinning places a small coating of solder over the wire and makes it easier to work with and solder to the circuit board. It also makes the wire stronger and able to put up with some bending without individual strands breaking off.

How To Tin A Wire

First, the bare stranded wire is twisted to make a tight rigid tube with all the wires going in the same direction. Then, solder is applied to the tip of the soldering iron and the tip applied to the wire. Melt a small amount of solder onto the wire until it is evenly coated. With the wire tinned in this way, it can easily be pushed through a hole in the circuit board, or bent into a shape that it needs to be in, or wrapped around a screw before it is tightened down.