ESD Models (Page 2 of 2)

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The Charged Device Model (CDM)

Not all ESD events involve the transfer of charge into the device.  Electrostatic discharge from a charged device to another body is also a form of ESD, and a quite commonly encountered one at that. 

A device can accumulate charge in a variety of ways, especially in situations where they undergo movement while in contact with another object, such as when sliding down a track or feeder.  If they come into contact with another conductive body that is at a lower potential, it discharges into that body.  Such an ESD event is known as Charged Device Model ESD, which can even be more destructive than HBM ESD (despite its shorter pulse duration) because of its high current.

There are currently two widely-used models for CDM testing: 1) the Socketted Discharge Model (SDM); and 2) the Real-world Charged Device Model (RCDM).  SDM simulates a device inserted in a socket, then charged from a high voltage source, and then discharged through a 1-ohm resistor.  SDM is easy to conduct but is not always replicating real-world CDM ESD events.

RCDM testing consists of putting the DUT in deadbug position on a thin dielectric (FR4), which is then placed over a ground plate.  The DUT is then charged either directly by a charging probe or indirectly by field induction.  Each pin is then discharged through a 1-ohm resistor to ground.

Two examples of industry standards that define CDM ESD testing are JEDEC's JESD22-C101 and  ESD Association's ESD STM5.3.1: Electrostatic Discharge Sensitivity Testing -- Charged Device Model.  

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See also:   What is ESD?;  ESD Test Waveforms;  ESDS Levels;  ESD Failures;  ESD Standards; 

ESD Controls;  ESD Audit Checklist;  The Triboelectric Series