Hardware Reference
In-Depth Information
Electrostatic Discharge Protection
When you are working on the internal components of a computer, you must take the necessary
precautions to prevent accidental static discharges to the components. At any time, your body can
hold a large static voltage charge that can easily damage components of your system. Before I ever
put my hands into an open system, I touch a bare metal grounded portion of the chassis, such as the
internal frame or the power supply case. This action serves to equalize the electrical charges that the
device and my body might be carrying. Be sure the system is unplugged during all phases of the
assembly process. Some will claim that you should leave the system plugged in to provide an earth
ground through the power cord and outlet, but that is unnecessary. If you leave the system plugged in,
you open yourself up to other problems, such as accidentally turning it on or leaving it on when
installing a board or device, which can damage the motherboard or other devices.
Caution
Power supplies used in many systems today deliver a +5V current to the motherboard
continuously—that is, whenever they are plugged in. Bottom line: Be sure any system you are
working on is completely unplugged from the wall outlet.
A more sophisticated way to equalize the charges between you and any of the system components is to
use an electrostatic discharge (ESD) protection kit. These kits consist of a wrist strap and mat, with
ground wires for attachment to the system chassis. When you are going to work on a system, you place
the mat next to the system unit. Next, you clip the ground wire to both the mat and an unpainted part of
the system's chassis, tying the grounds together. You then put on the wrist strap and attach that wire to
either the chassis or the mat. If you are using a wrist strap without a mat, clip the wrist-strap wire to
the system chassis. When clipping these wires to the chassis, be sure to use an area that is free of
paint so a good ground contact can be achieved. This setup ensures that any electrical charges are
carried equally by you and any of the components in the system, preventing the sudden flow of static
electricity that can damage the circuits.
As you install or remove drives, adapter cards, and especially delicate items such as the entire
motherboard, memory modules, or processors, you should place these components on the static mat.
Sometimes people put the system unit on top of the mat, but the unit should be alongside the mat so
you have room to lay out all the components as you work with them. If you are going to remove the
motherboard from a system, be sure you leave enough room for it on the mat.
If you do not have such a mat, place the removed circuits and devices on a clean desk or table.
Always pick up a loose adapter card by the metal bracket used to secure the card to the system. This
bracket is tied into the ground circuitry of the card, so by touching the bracket first, you prevent a
discharge from damaging the components of the card. If the circuit board has no metal bracket (a
motherboard, for example), handle the board carefully by the edges, and try not to touch any of the
connectors or components. If you don't have proper ESD equipment such as a wrist strap or mat, be
sure to periodically touch the chassis while working inside the system to equalize any charge you
might have built up.
Caution
Some people recommend placing loose circuit boards and chips on sheets of aluminum foil. I
