ESD - Electrostatic Discharge
ESD is simply
the discharge of built up static electricity. Electrostatic
discharge however, should not be taken lightly when working
with computers. ESD has the capability of causing enough damage
to the components inside your computer to render it completely
inoperable. It's important to use an anti-static strap and/or
a grounding mat whenever working on the inside of your computer.
Being aware of ESD precautions can significantly reduce the
chance of damage to your computer due to static electricity.
Static electricity is a fact of Life. You're producing it and
discharging it constantly. Moisture in the air can help it to
dissipate, and raising the humidity in your workplace is another
very good measure you can take to reduce the chance of damage
caused by ESD. ESD is bad for computers and electronic components.
If you are opening the case or working inside a computer, always
take ESD precautions.
There are capacitors inside a computer's monitor
and power supply that store enough electricity
to stop your heart, even when they are unplugged. You should
not be grounded if you are working inside a monitor
or a power supply.
But then, you shouldn't even open a monitor
or a power supply unless you know what you're doing.
How Much is Too Much?
Have you ever walked across a carpet
on a dry winter day, touched somebody, and heard the snap of
electricity as a small blue spark jumped from your fingertip
to the edge of your victims ear?
If the discharge was felt,
it was probably more than 2000 volts. If you heard
it, then it could have been between 3000 - 5000 volts.
If you actually saw a small blue spark, it was more than
likely in excess of 10,000 volts.
So do I have to walk on a
shag rug? Does it have to be a dry winter day? No! Your body
is building up and discharging static electricity all the
time. Just shifting in your chair can produce up to 150
- 200 volts! You can't completely eliminate this problem but
it can be controlled.
ESD and Your Computer
The ICs (Integrated Circuit chips) on
the various circuit boards in your computer use between 2 -
5 volts. They can be damaged by less than 200 volts.
Some may be damaged by as little as 30 volts. This means that
ESD can cause damage to the various components inside your computer
and you won't feel it, hear it, or see it. In fact, the discharge
voltage could be 1000 times less than what the human body can
When they started replacing
the tubes in radios with transistors, people were amazed at
how small radios were getting. You could get a transistor
radio that boasted 7 transistors and was about the size
of a brick!
Today, some of the individual chips on your
computer's circuit boards contain millions of transistors.
Advancements in technology allowed for entire circuits to be
etched onto a single chip. These are called Integrated Circuit
One technology for
producing ICs is called TTL (Transistor Transistor Logic).
These chips are actually more tolerant of ESD and even faster
than the newer technology. However, they're also larger, use
more electricity or power, and their resistance causes them
to run very hot. As computer technology advanced and the number
of transistors in the chips increased, heat and power consumption
became a huge problem.
TTL ICs are still used
in computers today, but the newer CMOS chips
(Complimentary Metal-Oxide Semiconductor) have
all but replaced them entirely. These chips have a semi-conductive
metal oxide layer that allows for less resistance, reducing
the power consumption and the generated heat. Unfortunately,
the very technology that makes these CMOS chips more efficient
also makes them very susceptible to electrostatic discharge.
Wait a minute! If you can
discharge 10,000 volts of static electricity into somebody's
ear, how come it doesn't kill them? Well, the amperage is very
low. The human body is very tolerant of voltage, it's the amperage,
or a current's strength, that will kill you. The chips inside
your computer however, are highly sensitive to any kind of voltage,
even at very low amperages. ...By the way, all of today's
CPUs (Central Processing Units) and system memory chips on your
RAM SIMMs or DIMMs are CMOS chips.
So what kind of damage can be caused
by ESD? Anything from a simple system interruption, causing
your computer to reboot with no further problems, to complete
destruction of a chip that will make your system unusable until
the chip is replaced. Also, you won't find any discoloration,
burn mark or physical indication whatsoever as to which chip
has been damaged.
There are 2 types of damage
that can occur:
Immediate Failures (Direct Failures,
Catastrophic Failures) - These are failures that occur immediately
after the chip has been damaged and usually aren't recoverable
until the chip has been replaced. Say you open your computer
(or worse yet, someone else's) to install more memory. Without
using an anti-static strap or a grounding mat (you've done it
lots of times before and never had a problem), you take a brand
new DIMM from its anti-static tube, install it, and now the
computer won't even finish its boot sequence. Not a good situation,
but you do know the computer worked before you installed the
RAM, so you should have an idea where to start looking for the
Latent Failures (Upset Failures,
Delayed Failures) - Sometimes a chip can be damaged by electrostatic
discharge and the results aren't immediately noticeable. Months
later the chip could finally fail completely, or you may end
up with intermittent failures that occur sporadically. These
are usually difficult to attribute to any specific cause, and
very hard to track down.