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ANSI/ESD-S20.20-1999
7. APPENDIX A - SENSITIVITY TESTING
7.1. ESD Sensitivity Testing
Technical literature and failure analysis data exist that indicates ESD failures are due to a complex series
of interrelated effects. Some of the factors that influence ESD sensitivity include the ESD current and
energy envelope, the rise time of the ESD event, device design, fabrication technology and device
package style. Energy sensitive devices are damaged by currents through the resistance of a bipolar
junction, protection resistor, or protection MOS transistor. Voltage sensitive devices are damaged when
the breakdown voltage is exceeded. ESD Sensitivity Testing of devices, whether performed using the
Charged Device Model (CDM), Machine Model (MM) or the Human Body Model (HBM), provide ESD
sensitivity levels for the comparison of one device to another using defined parameters. The ESD
sensitivity of the device (defined in volts), as determined by using any of the defined models, may not be
the actual failure voltage level in the manufacturing, process or user environment. Table 2 provides a
reference for various standards and test methods for ESD sensitivity testing.
7.1.1. Human Body Model Sensitivity:
A source of ESD damage is the charged human body, as modeled by HBM standards. This testing
model represents the discharge from the fingertip of a standing individual delivered to the conductive
leads of the device. It is modeled by a 100 pF capacitor discharged through a switching component and
1,500 ohm series resistor into the device under test. The discharge itself is a double exponential
waveform with a rise time of 2-10 nanoseconds and a pulse duration of approximately 150 nanoseconds.
The use of a 1,500 ohm series resistor means this model approximates a current source. All devices
should be considered as HBM sensitive. The HBM ESD sensitivity of devices may be determined by
testing the device using one of the referenced test methods. HBM sensitivities can be found in RAC
VZAP, Qualified Manufacturers, List of Products (QML-19500) or Qualified Manufacturer List (QML-
38535).
7.1.2. Machine Model Sensitivity:
A source of damage for the MM is a rapid transfer of energy from a charged conductor to the conductive
leads of the device. This ESD model is a 200 pF capacitor discharged through a 500 nH inductor directly
into the device with no series resistor. Due to the lack of a series current limiting resistor, this model
approximates a voltage source. In the real world this model represents a rapid discharge from items such
as, charged board assembly, charged cables, or the conduction arm of an automatic tester. The
discharge itself is a sinusoidal decaying waveform with a rise time of 5-8 nanoseconds and a period of
approximately 80 nanoseconds.
7.1.3. Charged Device Model Sensitivity:
A source of damage for the CDM is the rapid discharge of energy from a charged device. The ESD event
is totally device dependent, but its location relative to ground can influence the failure level in the real
world. The assumption for this test model is that the device itself has become charged and rapid
discharge occurs when the charged device’s conductive leads contact a metallic surface, which is at a
different potential. A major issue with the preparation of a CDM test standard is the availability of suitable
instrumentation to measure the discharge event. The waveform rise time is often less than 200
picoseconds. The entire event can take place in less than 2.0 nanoseconds. Although very short in
duration, current levels can reach several tens of amperes during discharge.
Table 2 - ESD Susceptibility Test References for Devices
ESD Standards and Methods for Susceptibility Testing of
Devices
ESD STM5.1
MIL-STD-883 Method 3015
MIL-STD-750 Method 1020
MIL-PRF-19500
MIL-PRF-38535
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