Dear Jim,
Thanks for taking the time to read the standard. Let me expand on the
justification of the changes.
Table of Content
----------------
1) New current target
2) On the correlation problems with ESD testing
3) Specific answers to your points (marked by ### in your email)
David Pommerenke
University Missouri Rolla
1) New current target
=====================
If you accept that a larger calibration bandwidth is needed (see my
point (2)) then there is a need for a new target. The present target is
only useful up to 1 GHz. Above 1 GHz targets that are build the "same"
way differ a lot. The present target also has a high input impedance in
the RF range (it reaches kOhm), so that the current is disturbed
relative to a large ground plane.
Now a target also needs to be calibrated, as one needs to determine if
it fulfills its specification. This requires a
either
a network analyzer
or a spectrum analyzer with tracking
or a signal generator and a power meter.
or a TDR in TDT arrangement.
The good news is that this is only relevant for the manufacturer of the
target, NOT FOR THE USER of the target.
Now the construction of the new target is quite simple. I have made
about 10 in the last years. There are also other constructions possible
that are more simple. Note the target information is information, i.e.,
everyone can make their own target, as long as it measures correctly the
construction does not matter.
2) On the correlation problems with ESD testing.
================================================
Every ESD test is a combination of many physical tests. Disruption or
disturbance can be caused by:
a) dielectric breakdown
b) Current (ohmic loss -> thermal)
c) Induction -> voltage -> oxid breakdown
d) Induction -> current -> thermal
e) Induction -> disturbance
f) Ohmic voltage drop -> disturbance
g) Inductive voltage drop -> disturbance
And there are many more. For each of them the question:
- Is an ESD test reproducible?
Will have a different answer. For example, the dielectric breakdown is
strongly related to the voltage, and the voltage of ESD generators is
well controlled.
Now modern ICs can react to pulses of about 50ps width (just look at
your PC). Now, induction is a differentiation process, e.g., it is a
high-pass filter. The high frequency components of the current and the
transient fields will dominate the circuit response (in this case:
mostly disturbance, not destruction).
If you compare the high frequency components of different ESD generator
currents and fields, you will see differences larger than 20dB. As a
consequence, failure levels for fast ICs (disturbance) will vary as much
as 1:5 if ONLY the ESD generator is changed.
This has been observed in many Industry applications and tests and is
the main driving force for improving the standard.
We are in the process of publishing results of such correlation under
well controlled conditions and the analysis of the reasons (correlation:
ESD generator parameters vs. disturbance failure levels).
The paper is in the review-process of the IEEE Transactions on EMC. I
will not post it here while it is in review, but I can email a pre-print
version to interested individuals.
From: Jim Ericson [mailto:[email protected]]
Sent: Tuesday, May 06, 2003 12:02 AM
To: Pommerenke, David; emcpost
Subject: Re: current-sensing transducer photos
David:
Thank you for the Committee Draft Version of the new ESD Standard. The
committee is to be commended for producing such a thoroughly researched
document that aims at improving test reproducibility of such a complex
event as electrostatic discharge.
While I am personally fascinated with the "scientific" aspects of ESD, I
must say that the CDV rather took my breath away ... from the standpoint
of
ESD Current Target/Conical Adapter Line mechanical complexity ... to the
cost implications for the EMC Laboratories and their clients. 4 GHz
Current
Targets, Network Analyzers, Oscilloscopes, and Electrostatic Voltmeters
are
far from trivial expenditures for any Laboratory.
##### Most test labs neither build ESD-current targets, not do they
calibrate ESD generators themselves. For ESD-target and ESD-generator
manufacturers, it is quire reasonable to expect that they can
characterize the device they are building or calibrating.
#####
I guess what I am missing is the underlying justification of need to
change
>from the current 1 GHz approach.
###### Please see my text above. There are more references that should
be part of the CDV, they may also be in a "justification" document.#####
I don't mean to beat this subject into a dead horse. I am not qualified
to
do that (even if I wanted to) either from experience or education. I
would
only make the following comments from my perceptions based on 7 years
with
an EMC Lab, and 18 years building, testing, and evaluating Silicon for a
couple of semiconductor
manufacturers:
1. In the several years of performing (or directly supervising) ESD
Compliance
testing at the lab, I have very seldom seen cases of correlation
problems
THAT
WERE NOT FOUND TO BE THE RESULT OF ONE OR THE OTHER PARTIES FAILING TO
FOLLOW THE EXISTING ESD STANDARD.
###### Following the standard is needed anyway. There are large problems
with reproducibility for disturbances in fast systems. With increased
use of fast ICs this would get worse and worse if not fixed now. Please
see my comments above also.
#######
2. Our lab has often also been involved in testing multiple samples of
various
EUT models to 20 kV and beyond (for design verification, not
Compliance).
Very seldom was there any difficulty
correlating with the manufacturer.
3. If good engineering practice is used in designing PCB layouts,
wiring
layouts, grounding, etc., even complex mixed-analog/digital EUTs can
easily
meet the 8 kV Air/4 kV Contact ESD requirements by a good margin. It's
not
that difficult to achieve. And that is a good thing, because the "real
world" of carpeted environments and "floating" users often generates
voltages substantially above 10 kilovolts.
#### You are right, in most cases this should not be a large problems.
Now if the board-layer count is reduced to save cost, no planes are
allowed for the same reasons etc. ESD is a problem. Of course, with
enough money used on boards and shielding ESD is not a problem. The same
is true for emissions.
#####
4. In short, an EMC Lab is in the Compliance business, not the Science
bus
iness. The "real world" rationale of most EMC Standards is, by and
large,
clearly understood by me. I guess I am somehow missing said rationale
for
the 4
GHz CDV of the ESD Standard.
#####
Note, only the ESD target is specified up to 4 GHz. The ESD generator is
specified up to 2 GHz.
There is an informative annex that contains transient field information
(as a guideline to the manufacturers) that is valid up to 2 GHz.
There is information on the voltage induced in a loop (informative
annex, as a guideline for ESD generator manufacturers). This information
is valid up to 4 GHz.
######
Sincerely,
Jim Ericson
Quality System Manager/Sr. EMC Engineer
Acme Testing Company
Acme, WA
[email protected]
----- Original Message -----
From: "Pommerenke, David" <[email protected]>
To: "Jim Ericson" <[email protected]>; "drcuthbert" <[email protected]>
Cc: "Dan Kinney (A)" <[email protected]>
Sent: Sunday, May 04, 2003 1:44 PM
Subject: RE: current-sensing transducer photos
Dear Jim,
If one builds a target now, I suggest to build the new version of the
target, as the new version is defined up to 4 GHz, while the old version
will not work beyond 1 GHz.
The new version is the the latest CDV of the standard which I attach.
David Pommerenke
From: Jim Ericson [mailto:[email protected]]
Sent: Saturday, May 03, 2003 6:23 PM
To: drcuthbert
Cc: Pommerenke, David; Dan Kinney (A)
Subject: current-sensing transducer photos
Hi Dave:
Photos attached include:
001 - front side of target showing the center contact disc where you
place
the sharp contact point of the esd gun.
002 - rear side of target showing the "N" connector.
003 - closeup of the front side with the contact disc unscrewed. If you
zoom a little, you can see some of the radially-spaced 51 Ohm resistors
on
the right side.
Regards,
Jim Ericson
Acme Testing Company
[email protected]
note: [email protected] is my home address.
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