Colleagues,
I raised the question a few weeks ago of the 'correct' level of ESD immunity
that should be chosen, in the particular field of plastic-bodied electronic
products. With these products, it is generally the CONTACT or DIRECT
discharge that is the problem, whereby a discharge penetrates the case via
seams or apertures. As I said then, my problem is that the 'official' ESD
standards do not seem to go far enough in guaranteeing ESD protection, under
extreme conditions.
Let me start by thanking those people who already contacted me with
contributions.
I am aware of the following standards which address ESD:
(The voltages refer to direct or contact discharge.)
IEC 801-2 (1984) 8kV
MIL-STD-1686C, ESD Class 1 2kV
MIL-STD-1686C, ESD Class 2 4kV
MIL-STD-1686C, ESD Class 3 16kV
ECMA TR/40 8kV
ANSI C63 8kV
MIL-STD-883, Method 3015 Cat A12kV
MIL-STD-883, Method 3015 Cat B2 'above 2kV'
Unfortunately MDS-201-0004 makes no mention of ESD.
So much for the standards. What 'real-life' ESD voltages can be expected?
The classic table that keeps coming up in the literature appears to
originate from the US DOD:
-Activity - 10.2% RH 65.9% RH
Walking across carpet 35,000 V 1,5000 V
Walking across vinyl floor 12,000 V 250 V
Working at bench 6,000 V 100 V
Plastic folder with instructions7,000 V 600 V
Natural poly bag lifted from bench 20,000 V 1,200 V
Foam padded work chair 18,000 V1,500 V
The EMC text books also indicate that one can see up 35kV on a human in
extreme conditions (dry and cold).
My specific interest in all this is that I am dealing with a family of
products that keep failing in the field (particularly cold dry places) and
it is suspected that ESD is the problem. It is further felt that the ESD
testing that has been done (to 8kV, as per IEC801) probably isn't enough.
However, no-one knows where to go from here.
So...
-Can anyone advise on other ESD standards that I have missed?
-Do large companies have their own internal ESD standards that go futher
than the commercial ones?
-Is there good reference information available on the human voltages that
can be seen in real life?
-What do you test to?
As before, I will mail a summary to the group of any relevant info received.
Many thanks
--Paul Reilly--
PA Consulting Group
Cambridge UK, Tel UK + 1763-261222
paul.rei...@pa-consulting.com
(Sorry for this long msg: if you're replying, please edit down).
