Nuts and Volts - February 2009

solder with the board or wires moving all over the place. It may be necessary to use a small vise or other gripping tool to hold the board or wires steady while you solder.

Care Is Required

Contact the Author

You can reach James Antonakos at antonakos_j@sunybroome.edu or visit his website at www.sunybroome.edu/~antonakos_j.

There are a few problems to watch out for while soldering. First, you may accidentally create a solder bridge. This is a blob of solder that fills the gaps between two different soldered connections. For example, on a PCB the copper pads where component leads are soldered are sometimes very close to each other. If too much solder is applied to one copper pad, it may overflow and spill over to another pad. The solder has now made an electrical connection between the two copper pads. This connection is called a solder bridge. Unfortunately, this connection is not intended and changes the circuit. The change may prevent the circuit from working, create a short that blows a fuse when you apply power, or have some other negative effect on the circuit's operation. For these reasons, the solder bridge must be removed. This is accomplished by reheating the solder that forms the bridge using the tip of the soldering iron. Sometimes you can use the tip to gently push the solder around enough to break the bridge. Solder — like water and other liquids — has surface tension when it is molten and will naturally try to bead together. If there is too much solder in the bridge, this method will not work and you will have to remove some of it. This can be done using a solder braid to absorb the extra solder. A solder braid is a stringy copper mesh that is heated and placed onto a blob of solder. When the solder melts, it transfers to the braid, coating it and filling the gaps in the mesh.

Another way to remove a solder bridge is to heat up the solder to make it melt and then suck it up with a solder sucker. This is a small handheld tool that uses a vacuum to pull the molten solder away from a copper pad or other connection.

It is important to understand that the solder is not melted by the soldering iron tip and then dripped onto the items being soldered. The solder must be melted by the heat of the items being soldered. Otherwise, you may encounter another problem called a cold solder joint. In this situation, the solder has cooled too quickly and becomes brittle. The solder may actually crumble

when it is wiggled. A cold solder joint typically makes a poor connection, as well. This may manifest itself as an intermittent problem that shows up and goes away in your circuit, especially when the circuit is moved. Unlike the bright, shiny, smooth surface of a proper solder connection, the cold solder joint looks flat and pitted. It is not difficult to make a cold solder joint. Simply blowing on the molten solder makes it cool quicker. It is best to let the solder cool on its own.

Protect Your Components!

Sometimes the component whose leads are being soldered is sensitive to heat. In order to protect it, a heatsink is used. The heatsink connects to the lead being soldered, gripping it tightly. If one is not available, an easy substitute is to take a pair of needle-nose pliers and wrap a rubber band around the handles. The rubber band will try to keep the pliers closed. Then, the pliers are used to grab the lead of the component being soldered. The better the grip the pliers have on the component lead, the more heat they will transfer away from it.

When you have finished using the soldering iron, it should be unplugged and allowed to cool before it is put away. While it is still hot, it is a good idea to clean the tip a final time with the wet sponge.

If you have never soldered before, how do you get started? A trip to RadioShack or some time spent in an electronics magazine (such as Nuts & Volts) will present you with an opportunity to buy a soldering iron kit complete with sponge and solder. And again, you also need something to solder. Buy an electronic project kit. Start small with a simple circuit that only has a few components, such as an LED flasher or a music board with a single integrated circuit. Build up your confidence by completing the simple circuit and getting the satisfaction of seeing it work when you turn it on. If it does not work, look for unsoldered leads, solder bridges, or components inserted incorrectly.