Dear Experts,
would like to ask if my device is lower than the limits of S20.20, is it a mandatory requirement that i do tailoring for the limits that i used even it within the limit of S20.20 sample are worksurface, i used the less 1x10E9.
thank you.
Rosalie,
ANSI/ESD S20.20 states in the scope “This document applies to organizations that manufacture, process, assemble, install, package, label, service, test, inspect, transport, or otherwise handle electrical or electronic parts, 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). Also, protection from isolated conductors is handled by limiting the voltage on isolated conductors to less than 35 volts.
Processes that include items susceptible to lower withstand voltages may require additional control elements or adjusted limits. Processes designed to handle items with a lower ESD withstand voltage can still claim compliance to this standard.”
Additional control elements or adjusted limits are not absolutely required but this is something highly recommended. To figure out what should be done would depend on your process and the amount below the HBM, CDM, or isolated conductor limit your device needs to go. Just lowering some limits or adding additional ESD elements without a careful process assessment may not reduce your ESD risk as you expect. Process assessment is not something easy to do either. It usually requires an experienced ESD factory controls expert. There are many ESD consultants out there including the ESDA LLC that could help with this. If you want to learn more on process assessment there is ANSI/ESD SP17.1 and soon there will be a process assessment certification course offered through the ESDA
You also mentioned “tailoring” in your question and I want to clarify that “tailoring” is only used if you want to relax the standard. You can always tighten the limits of ANSI/ESD S20.20 in your own ESD control plan.
hi Andy, does it mean that if i intend to use the limits of the standard, i do not violate any requirement of the S20.20 even if i do not have the adjusted limits?
Rosalie,
If you were audited to the ANSI/ESD S20.20 standard and you have stated lower CDM or HBM limits than in the standard, they would expect to see some change to your limits or a justification why this is not needed at least in areas that handle the more sensitive parts. If not done, it may not be a finding, but it could be a strong recommendation that may lead to a finding later if not implemented
The bigger question is why would I want to keep the ANSI/ESD S20.20 limits if I know I have more sensitive components than 100V HBM or 200V CDM. The whole goal of your ESD program is to reduce the risk of an ESD event from occurring. By not understanding your process and what limits should be implemented you may not be effectively reducing your ESD risk
i see.
thank you Andy.
When handling devices more sensitive than 100 v HBM or 200 v CDM, you need to understand your process and what ii is capable of. For example, if you handle 50 v HBM products and the floor/footwear system has peak voltages of 25 volts, then the ESD control program does not need to change. You may test flooring and footwear more often but the process is already capable of handing these devices.
Technically, a field induced CDM process ia already in place. Since the largest field allowed that the device can exsist in is 125 v/in, then technically a 125 CDM device can be used, but without any guardband. At this point it is a risk evaluation that is needed.
The limits of ANSI/ESD S20.20 are not hard limits where on one side everything is fine and just over the limits everything will fail. There is some safety factors already built into the standards.
thank you very much John.