Doug Lowe - Electronics All-in-One For Dummies

Seven hundred degrees Fahrenheit is pretty hot — certainly hot enough to burn your skin instantly on contact — so soldering is an inherently dangerous task. It isn’t extremely dangerous, as the amount of solder you actually use and the tools you use to solder are fairly small. So any burns you do receive are likely to be small. But they can be painful, so you should take great care whenever you’re soldering.

Soldering is especially useful for electronics because not only does it create a strong physical connection between metals, but it also creates an excellent conductive path for electric current to flow from one conductor to another. This is because the solder itself is an excellent conductor. For example, you can create a reasonably good connection between two wires simply by stripping the insulation off the ends of each wire and twisting them together. However, current can flow through only the areas that are actually physically touching. Even when twisted tightly together, most of the surface area of the two wires won’t actually be touching. But when you solder them, the solder flows through and around the twists, filling any gaps while connecting the entire surface area of both wires.

Soldering isn’t the same as braising or welding. Braising is similar to soldering, but instead of solder, metals with a higher melting point (usually 850 degrees Fahrenheit or more) are used. Braising forms a stronger bond than soldering. Welding is an entirely different process. In welding, the metals to be joined are actually melted. In liquid form, the metals intermix and they cool to form an extremely strong bond.

Before you can start soldering, you need to acquire some stuff, as described in the following sections.

A soldering iron — also called a soldering pencil — is the basic tool for soldering. Figure 7-1 shows a typical soldering iron.

FIGURE 7-1:A soldering iron.

Here are some things to look for when purchasing a soldering iron:

The wattage rating should be between 20 and 50 watts. Note that the wattage doesn’t control how hot the soldering iron gets. Instead, it controls how fast it heats up and how fast it regains its normal operating temperature after completing each solder joint. (Each time you solder, the tip of the soldering iron cools a bit as it transfers its heat to the wires you’re joining and to the solder itself. A higher-wattage soldering iron can maintain a stable temperature longer while you’re soldering a connection and can reheat itself faster in between.)

The tip should be replaceable. When you buy your soldering iron, buy a few extra tips so you’ll have replacements handy when you need them.

Although you can buy a soldering iron by itself for under $10, I suggest you spend a few more dollars and buy a soldering station that includes an integrated stand. A good, secure place to rest your soldering iron when not in use is essential. Without a good stand, I guarantee that your workbench will soon be covered with unsightly burn marks. (The soldering iron, shown in Figure 7-1, includes a soldering station.)

A ground three-prong power plug is desirable but not essential.The grounding helps prevent static discharges that can damage some sensitive electronic components when you solder them.

More expensive models have built-in temperature control. Although not necessary, temperature control is a nice feature if you’ll be doing a lot of soldering.

Some models also have built-in static discharge. This can help eliminate the chance of damaging your circuit’s components while you’re soldering them.

Solder, the soft metal that’s used to create solder joints, is an alloy of tin and lead. Most solders are 60 percent tin and 40 percent lead, but that ratio may vary a bit.

Although solder is wound on spools and looks like wire, it’s actually a thin hollow tube that has a thin core of rosin in the center. This rosin, called the flux, plays a crucial role in the soldering process. It has a slightly lower melting point than the tin/lead alloy, and so it melts just a few moments before the tin/lead mixture melts. The flux prepares the metals to be joined by cleaning and lubricating the surfaces to be joined.

Solder comes in various thicknesses, and you’ll need to have several different thicknesses on hand for different types of work. I suggest you start with three spools: 0.062 inch, 0.032 inch, and 0.020 inch. You’ll use the 0.032 inch for most work, but the thick stuff (0.062 inch) comes in handy for soldering larger stranded wires — and the fine solder (0.020 inch) is useful for delicate soldering jobs on small components.

Solder is about 40 percent lead, and as you probably know, lead poisoning is a very real health hazard. Fortunately, your actual exposure to lead while soldering is pretty small. The smoke that often puffs up when you’re soldering is from the rosin flux, not from the lead or tin melting. Even so, it’s a good idea to always work in a well-ventilated area, and to wash your hands after soldering to remove any residual lead.

You can purchase lead-free solder, although it’s considerably more expensive than regular solder made from lead and tin. However, lead-free solder is more difficult to work with than normal solder and is less reliable. If you’re concerned about the long-term effects of working with leaded solder, I suggest you switch to lead-free solder but only after you’ve become proficient at working with leaded solder.

My attorney advised me to rewrite the previous paragraph to say that under no circumstance should you ever use solder that contains lead. He also insisted that I warn you to never plug your soldering iron in, lest it get hot and create the potential for burns, and that you should never ever connect your electronic circuits to actual electricity because it could create a shock hazard. In fact, you shouldn’t even read this book because it could damage your eyes or cause a paper cut. Or you might accidentally drop it on your foot.

Do not buy acid-flux solder, which plumbers use to solder pipes. The acid in this type of solder will destroy your electronics projects.

Besides a soldering iron and solder, there are a few additional things you’ll need to have on hand for successful soldering. To wit:

Third-hand tool or vise: It takes at least three hands to solder: one to hold the items you’re soldering, one to hold the soldering iron, and one to hold the solder. Unless you actually have three hands, you need to use a third-hand tool, a vise, or some other resourceful device to hold the items you’re soldering so you can wield the soldering iron and the solder. (See Chapter 3of this minibook for photographs of a third-hand tool and a hobby vise.)