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Soldering Your Circuit Board

Electronics projects involve a lot of little bits called components (think transistors and capacitors, for example) and wire, and items like microphones and light bulbs and such. In many instances, you have to solder some of these things together to provide an electrical connection between them.

Solder is a metal material that you melt and apply to two items; when it cools, it forms a joint that holds items together and forms an electrical connection. So why do you need to solder if you use solderless breadboards? Although we chose to not have you make circuits permanent by soldering them for the purpose of the projects in this book, we do ask you to solder wires to switches and microphones and such, so this is definitely something you need to be able to do.

Soldering perfect joints is an acquired skill — one that you just get better at with practice. Here are some valuable tips for getting started. Please, please read the several safety precautions about soldering in "Avoiding shocks". You’re playing around with 700°F temperatures here, and we don’t want you to get hurt!

Using a soldering iron

A soldering iron (sometimes called a soldering pencil) is like a wand that gets very, very hot so that when you touch it to the solder, it melts it. You can find a variety of soldering iron models (see an example in Figure 4-11), which will vary in price based on features, such as those we discuss in "Gathering Tools".

figure 4-11

When you’re ready to solder, make sure you attach the best tip for the job; a smaller conical or chiseled tip is your best bet. Then, make sure that the soldering iron is firmly seated in its holder. Finally, wait for it to reach the right temperature, somewhere around 700°F. Just touch the end of your solder to the tip, if the solder quickly melts, the iron is hot enough.

Before using a new solder iron — and periodically, as you use your iron — you should tin it (coat the tip with solder):

1. Heat up the iron.

2. Clean the tip by wiping it on a moist sponge.

3. Apply a little bit of solder to the tip.

4. Wipe off any extra solder with a moist sponge.

Working with solder

Solder is a rather soft metal, and the most common type for electronics projects is a 60/40 rosin core. The rosin core contains flux, which cleans the surface of the wires being soldered. This helps the solder stick to the wire surface.

Solder also comes in different diameters. You don’t need super-thick solder for electronics projects. We use 0.032" diameter solder on the projects in this book. Molten solder sends out fumes that you wouldn’t want your worst enemy to breathe. Lead-free solder helps you avoid toxic lead fumes. Keep your workspace well ventilated no matter what kind of solder you use.

When you solder, you press the cold (solid) solder to a part and then apply heat to a part you want to join, not to the solder itself (see Figure 4-12).


figure 4-12

When you solder, hold the soldering iron just as you would a pencil (near the base) and be careful to avoid touching the very hot tip. Touch the iron to the elements that will be joined to heat them and then feed solder onto them. The solder should flow like how water flows around your finger when you hold it under a running faucet. When you’re done soldering, pull the solder and the iron away, and let the solder cool that you applied. Take a look at the joint you made; it should be shiny and shaped like a little mountain (not a deflated soccer ball).

Here are some tips for good soldering:

Keep it clean. Make sure the parts that you solder are clean and that your soldering iron has a clean, tinned tip. See the preceding section for the skinny on tinning.


Watch the heat. Be sure to get the soldering iron hot enough and heat any parts you are soldering before you apply the solder.

Easy does it. You should need to hold the soldering iron on a joint only a few seconds.

If you heat a component for longer than a few seconds, you might damage it.

The eyes have it. Always wear safety glasses when soldering. Pockets in solder could pop when heat is applied. Your eyes are not the place for hot solder to settle.

Keep it clean, Part 2. Keep a damp (not dripping wet) sponge handy to wipe away excess solder on the tip and to wipe the tip clean before soldering each component.

Bend before you solder. Before soldering a wire onto a component, bend the end of the wire in a U shape and insert the U through the hole in the lug you want to solder to. Use a pair of needlenose pliers to clamp the wire to the lug. Then you can solder without having to hold the wire, the solder, and the soldering iron, which is nigh impossible (assuming you have only two hands).

Read about third-hand clamps in the upcoming section, “Soldering extras.” Figure 4-13 shows a switch and two potentiometers with wires soldered to the component lugs.

figure 4-13

Bend before you solder, Part 2. Before soldering a wire to a component that has presoldered flat contact pads, do the following:

1. Bend the end of the wire at a 45° angle.

2. Heat the end of the wire.

3. Apply a light solder coating to the wire.

4. Press the wire onto the contact pad with the soldering iron.

5. Hold down the wire with the soldering iron until the solder on the pad melts.

6. Remove the iron and hold the wire on the pad with your other hand until the solder cools. (You should hold the wire several inches from the solder joint so your fingers don’t get hot.)

Make sure that the component you’re soldering is kept steady. (Read about third-hand clamps in the next section for help with this.)

Figure 4-14 shows a microphone cartridge wire soldered with this technique.

figure 4-14

Soldering extras

Your soldering iron and solder are the main tools you need to make soldered joints. However, a few accessories will make your soldering life easier. These include Sponge: You use a damp (not dripping) sponge to wipe the tip of your soldering iron clean before soldering each component.

Tip cleaner: If you don’t keep the iron’s tip clean, it might actually repel solder — making it bead up and staying away from where you want it to go. When the tip is too grungy to be cleaned by simply wiping it on the damp sponge, use a tip cleaner paste to chemically clean it.

Solder wick: Sometimes you have to desolder a bad joint and then resolder it. To help remove the bad solder, you can use a solder wick, which is a flat, braided piece of copper that soaks up solder.

Third-hand clamp: There are fancy clamps you can buy called third-hand clamps to hold components while you solder them. Personally, we just use a vice and an alligator clip; they do just fine!