Protecting Electronic Components from Dreaded Static Discharge

You’re not the only thing in your work area that could suffer from shocks. Static discharge (also referred to as electrostatic discharge; ESD) can do damage to your delicate electrical components. Static discharge is so named because it’s caused by the discharge of electrons from a static charge that hang around in an insulating body, even after the source of those electrons goes away.

Static charge is typically caused by friction. You might trap some electrons in your body as you walk across a carpet, for example. When a static charge is built up on your body, a corresponding voltage difference is built up between your body and a grounded object, such as a doorknob. The zap when you then touch a doorknob is the static discharge: that is, the electrons flowing from you to the doorknob.

What static discharge can do

Metal oxide semiconductor (MOS) devices are cool because they allow integrated components to use less power. MOS devices improve circuit design and operation, but that improvement comes at a price. These little guys are VERY sensitive to ESD. One little zap, and they are likely to be history.

When you walk across a carpet, you can produce a static charge in the range of 2,000–4,000V. Because the number of electrons trapped on your body is low, you feel only a little shock. However, MOS devices contain a very thin layer of insulating glass that can become toast when exposed to as little as 50V of discharge or less. When you work with a MOS device, your body, clothes, and tools have to be free of static discharge. (You find out how to do that in the next section.)

MOS devices are found in many integrated circuits (ICs) and transistors. ICs and transistors that use bipolar devices do not have the very thin layers of insulating glass found in MOS devices, so they are less susceptible to damage from static discharge. Resistors, capacitors, diodes, transformers, and coils, on the other hand, aren’t in too much danger from static discharge. Keep static discharge away from your projects just to be safe.

How to guard against ESD

To get rid of static discharge in your electronics workshop, you can do several things, such as wearing anti-static devices and clothing, using static dissipative floor mats, and grounding your tools. First, wear an anti-static wrist strap. An anti-static wrist strap is one of the best ways to get rid of ESD. This strap, like the one shown in Figure 2-1, fits snugly on your wrist. You then attach the wire on the strap to earth ground — which is just what it sounds like: namely, the earth beneath your feet.

figure 2-1

The cold water pipe on a water heater or under a sink is a good option for earth ground — if the water pipes are metal, that is. Plastic water pipes that you find in some newer construction won’t work. Because the cold water pipe comes up out of the ground, it is therefore grounded (logical, huh?), which works where the hot water pipe usually won’t. Use a clamp to attach a wire to the pipe (earth ground) and run it to your worktable, being sure to

run the wire along the wall so you don’t trip over it. Set a loop of the wire at the edge of your worktable where it’s handy to attach the alligator clip on the end of it to your wrist strap. If you don’t happen to have a metal cold water pipe nearby, the best method is to use a metal rod that you insert into the ground. The standard rule is to sink it three feet deep. Second, wear clothing that is less likely to accumulate static charge. For example, polyester, acetate, and wool fabrics easily accumulate static charges whereas as cotton is less likely to accumulate the static charges necessary for ESD.Using an anti-static wrist strap and wearing cotton clothing will usually be sufficient.

Third, if you plan to do electronics projects long-term, consider buying a static-dissipative mat for your work surface. You connect the mat to a ground, as you do with the wrist strap, and the mat dissipates charges from components you’re working on as you lay them on the mat. However, the mat has a high enough resistance that it won’t short together the pins of components. There are also static-dissipative floor mats; however, these are more likely to be used in a manufacturing setting when a worker needs to move between workstations.

Anti-static wrist straps and static-dissipative workbench mats can be purchased at most electronics distributors. The prices for wrist straps vary widely but start at just over $6; prices for workbench mats start at about $10.

Don’t try rigging up a homemade anti-static wrist strap. The ones you buy have a high resistance that slowly dissipates current. If you use a material without that resistance, the current would rush to ground — which could cause you serious injury — instead of slowly dissipating. For $6, why take a chance?

Finally, don’t forget to ground your tools. Some tools, like the better soldering irons, have a three-prong plug that provides a ground connection. (Cheap tools might use only two-prong plugs, so avoid them at all cost.) Other than a grounded soldering iron, however, most metal tools (such as a screwdriver) dissipate static through you when you wear your handy anti-static wrist strap.

Working with the Tools of the Trade

In addition to keeping yourself safe from electricity, you will find a few other dangers with working with electronics projects. Using a variety of tools — from a hot soldering iron to a sharp hacksaw — mandates that you adopt some wise safety habits.

Safe soldering

Soldering poses a few different dangers. (You might use solder to attach various pieces of your electronics project, such as soldering wires onto a speaker, microphone, or switch.) The soldering iron itself (you can see one in Figure 2-2) gets mighty hot. The solder (the material you heat with the iron) gets hot. Occasionally, you even get an air pocket or impurity in solder that can pop as you heat it, splattering a little solder toward your face or onto your arm. To top that off, hot solder produces some nasty fumes.

figure 2-2

Soldering itself takes experience to get right. Your best bet is to have somebody who is good at it teach you. Here are some soldering safety guidelines you should always follow:

  • Always wear safety glasses when soldering.

  • Never solder a live circuit (one that is energized).

  • Soldering irons come in models that use different wattages. Use the right size soldering iron for your projects, as we discuss in Chapter 3; too much heat could ruin your board or components.

  • Solder in a well-ventilated space to prevent the mildly caustic and toxic fumes from building up and causing eye or throat irritation.

  • Always put your soldering iron back in its stand when not in use. Too, be sure that the stand is weighted enough or attached to your worktable so that it doesn’t topple over if you should brush against the cord.

  • NEVER place a hot soldering iron on your work surface. You could start a fire.

  • Give any soldered surface a minute or two to cool down before you touch it.

  • Never, ever try to catch a hot soldering iron if you drop it. No matter how hard you try, you are very likely to grab the hot end in a freefall. Let it fall; buy a new one if you have to — just don’t grab!

  • Never leave flammable items (like paper) near your soldering iron.

  • Be sure to unplug your soldering iron when you’re not around.

Don’t put your face too close to the soldering site because of the danger of stray hot solder and those horrible fumes. Instead, use a magnifying device to see when soldering teeny-tiny components to a board. You can buy clampon magnifiers that keep your hands free for soldering.