AN2434 Freescale Semiconductor / Motorola, AN2434 Datasheet - Page 22

• Manufacturer Part Number: AN2434
• Description: Input/Output (I/O) Pin Drivers
• Manufacturer: Freescale Semiconductor / Motorola

Appendix B
Reliability and Quality Assurance
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Austin, Texas 78735-8598
Electrostatic Discharge (ESD) in Integrated Circuits - A Primer
What is ESD?
Electrostatic Discharge is the application of a short duration high energy pulse to the external
leads of an integrated circuit.
both ESD and EOS failures are the direct result of localized heating, the location of the damage
differs.
while junction degradation, contact damage and gate oxide breaches are more often linked w i t h
ESD events. The reason for this difference in failure mechanisms is the rise time and duration
of the energy pulse. While ESD events may only take less than a microsecond to happen, EOS
events are much slower to occur, and typically last much longer.
An electrostatic discharge happens when two
with one another. Charge is transferred from one body to the other until they are both at the
same potential. The time required for this charge transfer to take place can vary, and depends
on the characteristics of the charged bodies, such as their capacitance and the resistance of the
discharge path between them. This charge transfer is referred to as an ESD event.
How can objects charge up?
Objects charge in a number of ways. Perhaps the most common is through frictional charging,
also known as triboelectric charging. This involves the transfer of electrons from one object
to another through direct contact.
separation, such as relative humidity.
when it's humid will not generate much charge, but in wintertime, when the relative humidity is
low, a substantial charge can be built up, only to be discharged via an ESD event when you touch
a lamp or doorknob. Objects can also charge up by being inside a strong electric field.
components in your television are in close proximity to the electric field generated by the
picture tube. When the TV is switched off, there is a great deal of static electricity on the
screen and case. Cracking and popping is also heard. This is the discharge of the field induced
charge that has built up on the various components inside the TV.
How are Motorola IC characterized with respect to ESD susceptibility?
In order to characterize devices, it is necessary to subject them to stresses that are
repeatable and predictable. This has resulted in the development of three ESD models used t o
approximate real world ESD events. The first two deal with a charged body discharging to o r
through an IC to ground, while the third simulates a charged IC discharging to ground.
The Human Body Model (HBM) is used to approximate what happens when a person, charged up
to some potential, discharges to or through an IC to ground. In this case, the human body has
been modeled as a capacitor of 100pF, discharging through a series resistance of 1.5K Ω .
real world situation and the model are depicted in Figure 1. When this capacitor is charged t o
2000V, it can deliver a peak current of 1.33A to the device under test!
~10nsec after the event began!
Damage seen on bond wires and die metallization are typically associated with EOS,
ESD is often confused with Electrical Overstress (EOS). While
Several factors can affect the efficiency of the charge
For example, walking across a carpet in summertime
objects at different potentials come in contact
This peak occurs only
(rev 2.0 - 5/5/95)
The
The
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