The ESD Models


  ***      According to the ANSI/ESD Association in standard S20.20-1999 there are three ESD models, as follow:

The Human Body (HBM)

Represents failure of an ESDS sensitive electronic device due to a discharge from a standing person's finger tip onto a part of a device which is directly or resistively connected to ground. As per the standard "it is modelled by a 100pF capacitor discharged through a switching component and 1.5KΩ series resistor into the device under test. The discharge itself is a double exponential waveform with a rise time of 2-10ns and a pulse duration of approximately 150ns". This model approximates a current source because of the series resistor.


Charged Device (CDM)

In this model, it is represented a rapid energy discharge from a conductive body onto an ESDS device. The failure occurs when a charged device is suddenly put in contact with a conductive body at a different potential. This event is difficult to measure, as per the standard "The waveform rise time is often less than 200ps. The entire event can take place in less than 2ns". However the expected discharge currents are expected to be high.


Machine (MM)

In this model it is assumed that the device has became charged and a rapid discharge occurs. This model is defined in the standard as "a 200pF capacitor discharged through a 500nH inductor directly into the device with no series resistor". This model approximates a voltage source because of the lack of a series resistor.