Dear Scott, (1) I have looked at quite a bit of literature that plots Failure propatibility vs. Stress level in contact mode like testing and have seen very few none-monotonic EUTs that show the none-monotonic behavior over a larger voltage range. (2) In my five year test practise at HP, I have only seen one EUT that failed at lower levels and passed at higher levels in contact mode. If you have data that shows"As others have said, I have seen numerous failures at less than the maximum required test voltage while the same system passes at the max required voltage." please share that data with me if it is in contact mode and if the number of discharges at each level is large enough to obtain an acceptable confidence level. Regards David Pommerenke
[Pommerenke, David] " -----Original Message----- From: Scott Douglas [mailto:dougl...@naradnetworks.com] Sent: Monday, June 10, 2002 4:46 PM To: emc-p...@majordomo.ieee.org Subject: RE: IEC 61000-4-2 ESD & 61000-4-5 Surge lower levels David, I disagree with you here. As others have said, I have seen numerous failures at less than the maximum required test voltage while the same system passes at the max required voltage. It seems to me the intent was / is / should be to verify product performance up to a maximum level, not just at that level. The logic here would be that the "standards writing group" would make the test cover reasonable ground up to some limit because it is quite common that anything up to that limit could happen. The reason for the limit is because it is uncommon for things larger / higher than the limit to happen. Contact discharge is the only way to make reliable and repeatable tests for ESD. No approach speed issues, etc. So testing at low levels and working up to a maximum limit is a reasonable test method. On the other hand, I find air discharge to be a difficult and not very repeatable test to do which causes me to question its usefulness. Yes, I agree that people interacting with products will more often see air discharge rather than contact discharge. But I also find it impossible to reliably repeat air discharge test results. The old approach speed, distance and coordinates of contact point issue. Until someone can make an automated air discharge tester that keeps human interactions out of the process, I can't see it being corrected. That said, testing at lower levels is just as necessary here. Regards, Scott Douglas Senior Compliance Engineer Narad Networks 515 Groton Road Westford, MA 01886 office: 978 589-1869 cell: 978-239-0693 dougl...@naradnetworks.com www.naradnetworks.com <http://www.naradnetworks.com/> At 08:36 AM 6/10/02 -0500, Pommerenke, David wrote: Dear Group, For most EUTs there is no need to do lower level testing in contact mode ESD. The time is better spend (meaning a better test results uncertainty is achieved) if the number of discharges is increased at the highest test level (hundreds is a good number). Although it is possible that a system fails at e.g., 2 kV contact mode (e.g., incomplete reset) and passes at 4 kV contact mode (full self-recovering quick reset) the likelyhood of that happening is not that large to require it in a standard. For air discharge lower level testing is needed, as the risetime is often much lower at lower voltages. Of course, if no discharge occurs, no further testing at even lower levels makes sense. I do know that what I am saying violates the present IEC 61000-4-2 standard. ut it reflects the coming version of IEC 61000-4-2. The standard does not intend to protect agains every possible ESD failure. I would like to receive your input, as I am one of the US-representatives in IEC TC77b WG-9 (ESD). David Pommerenke
