Chapter 1 Introduction to a Typical PC 25
a doorknob. You feel a sharp snap as the electrical
charge of your body discharges to the doorknob.
This is ESD.
You have learned about how ICs are
manufactured and can appreciate the small
scale of the circuit. An electrostatic discharge
will damage the tiny circuits inside the chip. To
prevent static discharge between two objects you
must create a condition where both objects are at
the same static voltage level or the same potential.
When two objects have the same static voltage
level, static discharge will not occur.
Technicians wear an anti-static wrist strap,
also called a ground strap, when handling static-
sensitive devices to avoid ESD, Figure 1-35. The
anti-static wrist strap is designed to create an
equal static voltage level between your body and
the object that the strap is connected to. To prevent
ESD damage to sensitive components you should
connect the alligator clip to the bare metal on the
computer case or power supply.
There may be times
when an anti-static wrist
strap is not available. You
can avoid ESD by touching the bare metal inside
the computer case with your hand, thus becoming
the same potential as the computer hardware.
Tech Tip
Figure 1-36 shows a red mat that provides an
anti-static surface for parts. The blue anti-static
wrist strap goes on the wrist and is designed to
bleed off any static buildup on a technician’s body,
allowing for the safe handling of static-sensitive
devices.
Electronic parts and devices are shipped inside
anti-static bags to prevent ESD, Figure 1-37. When
removing parts from a computer, place the parts
on an anti-static mat or inside an anti-static bag.
You will accumulate plenty of anti-static bags while
working as a computer technician. Every time you
install a part, such as a hard drive or a motherboard,
you will have an empty anti-static bag. Save the bag
for temporarily storing static-sensitive components
that you remove from a computer.
Be familiar with anti-static procedures,
specifically the use of anti-static straps and
mats and anti-static bags.
A+ Note
Electromagnetic Interference (EMI)
Electromagnetic interference (EMI) is
interference or damage to components caused
by magnets and magnetic fields. Any device that
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Figure 1-35. Anti-static wrist strap.
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Figure 1-36. Anti-static kit consisting of an anti-static wrist
strap and an anti-static mat.