01 March 2005
ELECTROSTATIC DISCHARGE (ESD)
mechanisms that cause avionics to fail in field service
and storage. In addition, procedures are outlined to
prevent these failures from occurring.
digital components are steadily increasing in functional
power, speed, and system applications in military
8-2. FACTORS INFLUENCING ESD. Maintenance
avionics. By making the VLSI devices small, less
of avionic equipment for ESD prevention requires an
voltage is needed to operate circuitry and the noise
understanding of the factors that contribute to ESD.
immunity decreases. Many of these devices are highly
Most modern aircraft electrical and electronic
susceptible to damage from the discharge of static
components are susceptible to conditions and activities
electricity. Electrostatic discharge (ESD) affects many
that can cause ESD; for example, walking on concrete
components such as transistors, resistors, integrated
floors, rubbing or separating materials, using
circuits (ICs), and other types of semiconductor
electrostatic copiers, or wearing synthetic clothing.
devices. A spark discharge resulting from the
Separating dry materials generates greater ESD than
accumulation of electrostatic charges may not
moist materials because moisture is conductive and
immediately destroy a device or cause it to become
helps to dissipate charge. For this reason, ESD effects
nonfunctional. The device can be permanently
are more noticeable in the winter since heating systems
damaged, yet perform its intended function. Additional
reduce moisture on the surfaces of furniture and other
exposure to spark discharges or continued use of the
objects. Any circumstances that results in a low relative
device can further damage the item until failure occurs.
humidity (RH) will permit a greater accumulation of
This is known as a latent failure and can seriously
affect a system's reliability. It is essential that everyone
involved in the repair handling, transporting, and storing
8-3. SOURCES OF AVIONIC ESD.
of electrostatic discharge sensitive (ESDS) items be
concerned about ESD. All ESDS items should be
8-3.1. CHARGING EFFECTS AND IC BREAKDOWN.
packaged, shipped, and stored in ESD protective
Static charge is generated as a result of direct or
materials. Further information on the Air Force ESD
indirect electrostatic field effects. The ESD problems
program is contained in TO 00-25-234.
that result from direct charge interaction with an IC are
caused by triboelectrically generated charges. That is,
8-1.2. DEFINITION. ESD is the transfer of electrostatic
charges that come in contact with the exposed leads of
charge between bodies with different electrostatic
the IC consequently cause breakdown. The indirect
potentials. This is caused by direct contact or induced
source of ESD is either by induction or capacitance
by an electrostatic field. The most formidable ESD is
change in the immediate environment. Inductive charge
lightning or electromagnetic pulse (EMP). Discharges
generation can be caused by a large static charge
from human bodies are the most frequent, least
away from an IC. This occurs if the charge is oriented
noticeable, and most ignored ESD. ESD affects
such that the IC receives an induced potential across
electronic devices in a number of different ways. It can
d e g r a d e performance, change the electrical
large static charge existing some distance away. This
characteristics, or cause complete failure of the device.
causes the charge distribution near the IC to vary
8-1.3. FAILURE MECHANISMS. Three of the most
ESD. For example, insulators near an IC can result in
common failure mechanisms are junction burnout,
direct charge contact sufficient to cause breakdown.
oxide punchthrough, and metallization burnout.
Junction burnout usually occurs in bipolar discrete
8-3.2. GENERATION OF STATIC CHARGES. Static
and integrated circuits. Metal Oxide Semiconductor
electrical charges are caused by the movement of
(MOS) discrete and integrated circuits often experience
dissimilar materials against one another. Generally,
oxide punch through. Metallization burnout is usually
these charges are attributed to some form of contact
associated with both bipolar and MOS ICs. The
between two dissimilar surfaces. The triboelectric series
f o l l o w i n g paragraphs describe some of the
is a list of materials in order of static charge generation.