67. Static Electricity Precautions

Some electronic parts are hyper-sensitive to static electricity. You can damage them just by touching them, if your body is charged up with static. This is especially likely in dry climates - if you live somewhere dry, you know how often you get zapped touching metal fixtures. And even if you don't notice blue sparks flying around, you can still have enough static charge on your body to damage IC chips and other especially sensitive devices.

There are some simple precautions you should take to avoid this danger when building circuit boards.

An easy way to tell that a particular part is static-sensitive is to look at its packaging. If it comes in one of those silvered mylar bags, it's probably sensitive to static.

The parts that are typically most sensitive to static are:

First, leave parts in their silvery bags until they're needed, and keep the bags closed. The bags provide good protection, so it's best to keep the parts there when you're not actively working with them.

When it comes time to install parts on a board, you obviously have to take them out of the bags. The basic rule for handling static-sensitive devices is to ground yourself early and often.

The term "grounding" is pretty literal. We're not talking about some kind of meditation exercise. We're talking about literally connecting yourself electrically to the soil around your house, to dump any excess static charge on your body into the ground. The Earth is basically an infinite reservoir of neutral charge, so excess charge naturally flows into the ground if given a path.

In practical terms, the thing to look for is an appliance with an unpainted metal case and a three-prong plug. Metal appliance cases are almost invariably wired to the third prong in the AC plug, which in turn connects in your house wiring to a big stake somewhere under the foundation that's driven into the dirt. As long as an appliance is plugged into a three-prong outlet, its metal case should be grounded.

A PC tower case is a pretty reliable example of this. The metal back plate (assuming it's unpainted) is a great grounding surface.

You don't have to keep one hand on a grounded surface the whole time you're working, although that would certainly be the ideal. A momentary touch is enough to discharge any static you've accumulated. Repeating this every few minutes while you're working will prevent new charge from building up.

Some rules of thumb:

You can buy a grounding wrist strap that keeps you continuously connected to ground while working - the equivalent of keeping one hand on a metal surface the whole time, but way more practical. A ground strap consists of a conductive bracelet that you wear around your wrist, and a wire that connects the strap to something grounded. Most types have an alligator clip at the other end of the cord that you're meant to attach to a grounded metal surface, so they assume that you have a grounded appliance or metal surface near your work area. You can also find grounding straps that plug into a three-prong outlet directly.

If you live in a dry climate, or you do a lot of electronics work, you might consider one of these. It's probably a bit more trouble than it's worth if you're only doing occasional hobbyist work. Maybe I've just been lucky, but in my experience, it's adequate to use the "touch a metal surface" technique as long as you're diligent about it.