Questions And Answers

If you have suspect ESD sensitive items and inspect the items and they pass all tests, you know that they have not experienced a catastrophic failure. But you do not know if a latent defect has occurred. According to the ESD Association “It is relatively easy with the proper equipment to confirm that a device has experienced catastrophic failure. Basic performance tests will substantiate device damage. However, latent defects are extremely difficult to prove or detect using current technology, especially after the device is assembled into a finished product.”

Here’s more information from the ESD Handbook ESD TR20.20 section 2.7 Device Damage:

“Electrostatic damage to electronic devices can occur at any point, from the manufacture of the device to field service of systems. Damage results from handling the devices in uncontrolled surroundings or when poor ESD control practices are used. Generally damage can manifest itself as a catastrophic failure, parametric change or undetected parametric change (latent defect).

2.7.1 Catastrophic Failures

When an electronic device is exposed to an ESD event it may no longer function. The ESD event may have caused a metal me lt, junction breakdown, or oxide failure. The device's circuitry is permanently damaged, resulting in a catastrophic failure.”

2.7.2 Latent Defects

A device that is exposed to an ESD event may be partially degraded, yet continue to perform its intended function. However, the operating life of the device may be reduced dramatically. A product or system incorporating devices with latent defects may experience a premature failure after the user places them in service. Such failures are usually costly to repair and in some applications may create personnel hazards. It is easy with the proper equipment to confirm that a device has experienced catastrophic failure or that a part is degraded or fails test parameters. Basic performance tests will substantiate device damage. However, latent defects are virtually impossible to prove or detect using current technology, especially after the device is assembled into a finished product. Some studies claim that the number of devices shipped to users with latent defects exceeds the number that fail catastrophically due to ESD in manufacturing. Other studies exist that claim that no failure mechanism exists to prove the existence of latent failures. To date, most studies contradict one another as to what magnitude of ESD damage can be attributed to latency.”