David,
Have been (still am) out of the office testing this week.
I am sorry to say that I cannot provide hard data to support my comments.
That experience was two lifetimes ago at a different employer. It happened
on more than one product model and on more than one of each model. I do
know that we would make 50 discharges at each test point. And, there were
more than ten test points on each model. Not every test point would exhibit
the problem, but those that did were consistent, something like 60% of
discharges would cause the system display to scramble. The peak failure
voltage was around 1.8 kV, with only a very few failures at 4 kV and none
at 8 or 15 kV. All were in contact mode.
This was all engineering work prior to official test house testing. We
identified the problems and made changes and re-tested. Once we got all
tests to pass, we would go for the official test. We had several of these
type of problems. Once was the scrambled (actually went black) LCD display.
Solved by shielding the cable to the display and termination resistors on
the display PCB. Another time was black lines in the recorded output (film
recorder products). This was corrected by proper grounding of the I/O
connector shell. Third time was system hang-up. If I recall this one
correctly, we added decoupling caps to chassis ground at the I/O connector
on the mother board. In all cases, the problems were at mid level tests,
usually 2 or 4 kV, rarely at 8 kV, and never at 15 kV.
Scott
At 08:33 PM 6/10/02 -0500, you wrote:
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
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