Why in ANSI/ESD S20.20 the ESD voltage HBM is different with voltage CDM?

In the foreword of ANSI/ESD S20.20:
This standard covers the requirements necessary to …assemblies and equipment susceptible to damage by electrostatic discharges greater than
or equal to 100 volts Human Body Model (HBM) and 200 volts Charged Device Model (CDM).

Why the volts HBM and volts CDM are different? Do this means 100volts-HBM has similar impact to ESDS with 200volts-CDM?

Thanks for anyone’s reply in advance.

Hello Nelson,
These two models are quite different from one another. The voltage level for one does not imply anything for the other. Each model will require different protection devices and imply different process requirements.
A brief explanation is that HBM is a two pin model so that one pin received the discharge and the other pin is grounded. Every pin-pair needs to be tested.
For CDM, the device is inductively charged and then one pin is discharged. In HBM, the packaging of the die does not matter, but in CDM it can influence the test quite a bit.
It also implies different process considerations. Simply put, HBM requires the control of personal while CDM required the control of insulators and devices themselves.
To fully understand the differences, there needs to be a understanding of the test standards and device failure modes. There are many classes offered by the ESD Association that could help explain the two models.
If there is something specific, please feel free to append the forum.

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Thanks a lot for the explanation, John.

Best regards