This lesson discusses a phenomenon that can damage or ruin sensitive electronic equipment—electrostatic discharge (ESD), sometimes referred to as static electricity. Fortunately, it is one of the easiest things to protect against.
After this lesson, you will be able to:
Estimated lesson time: 15 minutes
- Define ESD (electrostatic discharge).
- Avoid ESD.
The human body has an electric field and under the right (and very easy to obtain) conditions can generate a tremendous amount of voltage, often referred to as static electricity.
ESD occurs when an imbalance in the amounts of positive and negative electrical charges on the surface of an object is released. The most dramatic example of ESD is lightning, which splits trees as easily as it lights up the sky. The amount of energy released when you touch a metal object can be quite large. The buildup of energy with nylon clothes can easily reach 21,000 volts. About 750 volts are required to produce a visible spark with ESD, while a mere 10 volts or so can ruin a computer chip.
The actual amount of energy in a given ESD event depends on the types of materials involved (wool fabrics generate less than nylon), the humidity (low humidity offers less resistant to the discharge), the amount of physical energy (friction) involved, and how quickly the energy is released.
ESD does not have to be seen (a spark) to do damage to electronic components. Voltages lower than 10 volts can damage some parts.
Over the years, engineers have produced smaller and smaller components, which operate at lower and lower voltages. Their goal is to reduce size, cost, and operational heat production. Those are worthy goals, but because of reduced component size, they present a smaller target with less resistance to power surges. This makes the parts more susceptible to damage from ESD.
The amount of damage and resulting problems caused by ESD can be divided into three categories:
Prevention is the best defense against ESD, and the first step of prevention is to understand the source. The number one cause of ESD damage is improper handling of electronic devices. A semiconductor device can be damaged by ESD during handling before it is installed.
The key to ESD prevention is to keep all electronic components—and yourself—at a common electrical potential. This usually means ground potential, or zero volts. Maintain a habit of "grounding" yourself to the computer chassis whenever you attempt a repair. There are times when it is not practical, or convenient, to wear a ground strap. At such times, touching a part of the metal chassis before removing devices will bring you and the computer chassis to a common voltage. Don't move around while installing or handling a part; doing so can generate additional voltages, negating any effort you have made to eliminate ESD.
All repair shops and workbenches should have proper ESD-suppression devices, and technicians should use them whenever working with exposed parts. These devices include:
AC voltage can kill. Although the power used by the computer components is no more than 12 volts DC, many computers have 110 volts AC wired from the power supply to the on/off switch at the front of the computer case. This wiring can present a hazard. Never disconnect or remove boards from a computer with the power applied. This can damage the components.
Safety precautions are different for computer monitors. Never work on a monitor with the cabinet removed, power applied, and a wrist strap on; a wrist strap coming in contact with the high voltage wire (30,000 volts) can cause electrocution.
The following points summarize the main elements of this lesson: