[SI-LIST] Re: Testing chips with system level specs
- From: "Pommerenke, David" <davidjp@xxxxxxx>
- To: "Grasso, Charles" <Charles.Grasso@xxxxxxxxxxxx>, <doug@xxxxxxxxxx>, <dcuthbert@xxxxxxxxxx>
- Date: Wed, 6 Sep 2006 10:16:21 -0500
Charles,
On the "really fast discharges" using the Andy Hish simulatior I do not =
have the data here, as I am in Germany right now.=20
But if you look at
http://web.umr.edu/%7Etiumr/davidjp/Jour_Estat__high_qual_1995.pdf
(the link has %7 in it, that is OK)
at figure 10 and figure 11. You see measurements of discharges at 10kV =
having risetimes of about 100ps or so. That is very close to the limit =
of the measuremetn system (SCD5000).
The physics of the very fast discharges in air discharge is explained in
http://web.umr.edu/%7Etiumr/davidjp/ESDForum_1993.pdf
(kind of old paper, but the physics have not changed).
Regards,
David Pommerenke
-----Original Message-----
From: Grasso, Charles [mailto:Charles.Grasso@xxxxxxxxxxxx]
Sent: Wed 9/6/2006 9:44 AM
To: Pommerenke, David; doug@xxxxxxxxxx; dcuthbert@xxxxxxxxxx
Cc: SI-List; emc-pstc
Subject: RE: [SI-LIST] Re: Testing chips with system level specs
=20
David,
Can you please enumerate what "really fast discharges" are with the
Andy Hish generator @ 25kV?=20
Using the conical probe, the most prevalent discharge type I have seen
measured is a slow (ns) rise time pulse at the first strike as the probe
approaches the UUT and then a fast (ps)secondary spike as the probe
completes the contact to the UUT.=20
Best Regards
Charles Grasso
Compliance Engineer
Echostar Communications Corp.
Tel: 303-706-5467
Fax: 303-799-6222
Cell: 303-204-2974
Pager/Short Message: 3032042974@xxxxxxxxx
Email: charles.grasso@xxxxxxxxxxxx;
Email Alternate: chasgrasso@xxxxxxxx
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Pommerenke, David
Sent: Wednesday, September 06, 2006 7:04 AM
To: doug@xxxxxxxxxx; dcuthbert@xxxxxxxxxx
Cc: doug@xxxxxxxxxx; SI-List; emc-pstc
Subject: [SI-LIST] Re: Testing chips with system level specs
Doug,
it is all a matter or likelyhood. If you use rounded electrodes (no =3D
corona discharge) and dry air you will get really fast discharges up to
=3D
25k
V or so. We have measured such discharges usign the old Andy Hish =3D
simulator, but also with people.
If you look at the gemeotry of a memory card there are plenty of sharp =
=3D
edges. If we assume the card, or the cell phone or the camera is charged
=3D
to 8kV and you plug the card into the reader then there will be some =3D
corona. This corona will initiate the discharge over a larger distance =
=3D
(e.g, Paschen length for 8kV is about 2mm or so) and the discharge will
=3D
be soft. Without the corona the electrodes could approach further before
=3D
they the discharge is initiated. In summary, I agree that for such a =3D
geometry the likelyhood of sub-nanosecond discharges at 8kV is probably
=3D
low.
David Pommerenke
-----Original Message-----
From: Doug Smith [mailto:doug@xxxxxxxxxx]
Sent: Tue 9/5/2006 8:17 PM
To: dcuthbert@xxxxxxxxxx
Cc: doug@xxxxxxxxxx; Pommerenke, David; 'SI-List'; 'emc-pstc'
Subject: Re: [SI-LIST] Re: Testing chips with system level specs
=3D20
Hi David,
It is good to have lots of discussion on this. ESD is often only=3D20
considered when a gross problem surfaces. This discussion will help=3D20
bring the issue to the front.
What voltages were you using? Such fast events are common at low=3D20
voltages and rare at high voltages. I have personally measured =
edges=3D20
of <80 picoseconds at low voltages. For my chip example where slow=3D20
approach (say plugging in a memory card into a reader) is the norm, =
a=3D20
fast edge is probably not possible although I do not have=3D20
comprehensive data on this.
It seems one has to work at it to get a fast discharge at high=3D20
voltages, at least that is what I read through the lines. Hish =
et.al.=3D20
in a 1991 paper show three waveforms at about 10 kV, two slow and =
one=3D20
fast, but again they used a specific conical shaped tip with =
symmetry=3D20
that was required (that part was not spelled out clearly in the =
paper=3D20
but I was talking with a friend of Andy's). They said the =
likelihood=3D20
of the fast event was much smaller for a rounded tip.
Doug
David Cuthbert wrote:
> Doug,
>=3D20
> I've done some measurements of actual human body discharges into a 2 =
=3D
ohm
> current target. The rise time was less than 500 ps. I plan to continue
=3D
this
> work soon using a 2.5 GHz oscilloscope and a TDR. The human SPICE =3D
model I
> developed is quite interesting and I'll be refining it.=3D20
>=3D20
> I then built a circuit that quite accurately mimics the actual human =
=3D
body
> discharge. It is much more complex than the usual ESD gun =
network.=3D20
>=3D20
> Dave Cuthbert =3D20
>=3D20
>=3D20
> LINEAR TECHNOLOGY CORPORATION
> =3D20
>=3D20
> Internet Email Confidentiality Footer=3D20
>=3D20
> This e-mail transmission, and any documents, files or previous e-mail
> messages attached to it may contain confidential information that is =
=3D
legally
> privileged. IF you are not the intended recipient, or a person =3D
responsible
> for delivering it to the intended recipient, you are hereby notified =
=3D
that
> any disclosure, copying, distribution or use of any of the information
> contain in or attached to this transmission is STRICTLY PROHIBITED. If
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=3D
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manner.
> Thank You
>=3D20
>=3D20
>=3D20
> -----Original Message-----
> From: emc-pstc@xxxxxxxx [mailto:emc-pstc@xxxxxxxx] On Behalf Of Doug =
=3D
Smith
> Sent: Monday, September 04, 2006 11:15 AM
> To: davidjp@xxxxxxx
> Cc: SI-List; emc-pstc
> Subject: Re: [SI-LIST] Re: Testing chips with system level specs
>=3D20
> Hi David and the group,
>=3D20
> You have presented good data which you and others have presented =
in=3D20
> the various standards bodies we have attended together. However,
have=3D20
> you ever seen an air discharge with a 700 ps rise time at 8 kV? If so,
=3D
> what is the probability in the distribution of 8kV discharges? I=3D20
> measured a lot of discharges and none came close to that. Some had
a=3D20
> vestige of the initial spike, but it was not much larger that the body
=3D
> discharge after and its risetime was always much slower.
>=3D20
> If this concept was to be included in a standard, a lot of work
would=3D20
> be needed to determine the right amount of filtering.
>=3D20
> But, to apply this waveform (8 kV contact discharge) to a solid
state=3D20
> device like a flash memory card is not justified and will
needlessly=3D20
> increase device cost. I do agree that an 8kV contact discharge =
has=3D20
> uses in system level testing which what the 61000-4-2 standard =
was=3D20
> intended for.
>=3D20
> There is a LOT of work to apply that standard to devices, much =
more=3D20
> than the filtering I wrote about. There is no guidance in the standard
=3D
> as to how to apply the discharge and how it is applied will =
almost=3D20
> completely determine the results (other pins grounded or
ungrounded,=3D20
> if grounded how, and much more). If someone says their device
passes=3D20
> this test, the statement is meaningless at this point unless the
test=3D20
> method is documented.
>=3D20
> Doug
>=3D20
> Pommerenke, David wrote:
>=3D20
>>Group,
>>I like the idea from Doug to use a ferrite for reducing the risetime =
=3D
of a
>=3D20
> contact mode ESD generator. However, I do not agree to the statement =
=3D
that
> air discharge ESD will not show fast risetimes and high peak values at
> voltages above 4kV. The reference event for the ESD standard IEC =3D
61000-4-2
> is the discharge between a hand-held metal part and a large metallic =
=3D
surface
> (called "hand-metal ESD") in contrast to the IC-HBM standard that is =
=3D
based
> on a discharge from the skin.
>=3D20
>>The current has two maxima, an initial peak caused by the charges on =
=3D
teh
>=3D20
> hand and on the metal part and the later body waveform. If the initial
=3D
peak
> will show up depends on the resistance of the arc as a function of =3D
time. If
> the arc resistance drops quickly (let us say in less than 1ns) below =
=3D
the
> source impedance of the discharging person (without going into =3D
details,
> assume 100-300 Ohm http://web.umr.edu/~davidjp/paper/00478274.pdf ), =
=3D
then
> the inital peak will show up. If the arc resistance drops slowly, let
=3D
us say
> it reaches 300 Ohm in 5 ns, then the initial peak will not show up, as
=3D
the
> arc resistance is too high during this phase of the discharge.
>=3D20
>>So the quesion is: How fast does the arc resistance drop?
>>
>>This depends mainly on:
>>
>> - Voltage at the moment the discharge starts
>> - Gap distance at the moment the discharge starts
>>
>>The smaller the gap, the faster the arc resistance will drop. The gaps
>=3D20
> will in most cases not discharge over distances given by the =3D
Paschen-law,
> but at smaller distance. This is a result of the speed of appraoch and
=3D
the
> statistical time lag ().
>=3D20
>>In general the behavior is as follows:
>>
>> Fast rise times --- Slow rise times
>> =3D20
>> Fast approach slow approach
>> Dry air Moist iar
>> Clean surfaces Dirty surfaces
>> Oxid layer, or paint =3D20
>>=3D20
>>The effect of environmental conidtions on the discharge are very =3D
strong.
>=3D20
> Humidity dominates over all other influencing factors (I can email =3D
papers on
> this topic on request). It is not possible to state: Above XYZ kV =3D
discharges
> will not have an initial peak.
>=3D20
>>To provide further evidence I attached a set of measurements that show
=3D
the
>=3D20
> peak current as a function of voltage having the arc length as =3D
parameter.
> The data is from D.Pommerenke, ESD: Transient fields, arc simulation =
=3D
and
> rise time limits, Journal of Electrostatics, 36, 1995, 31-54.
>=3D20
>>However, the likelyhood of having fast risetimes (e..g, less than =3D
200ps)
>=3D20
> decreases above about 6-10 kV. Nobody knows the distribution of ESD
> intensity in reality very well. There are a few studies, but they only
=3D
help
> to answer the question of voltage distribution, not of rise time
> distribution or field strengths distribution.
>=3D20
>>Overall, I warn against changing the pulse parameters above some =3D
voltage
>=3D20
> without having strong evidence that the reduction in protection level
=3D
is
> acceptable, the 0.7ns-1ns risetime is already providing only partial
> coverage.=3D20
>=3D20
>>Products that may see many ESDs or support critical functions should
>=3D20
> certainly not be tested at a different waveform. The 0.7ns - 1ns rise
=3D
time
> standardized contact mode waveform certainly does not cover the faster
=3D
ESD
> events.
>=3D20
>>Regards,
>>
>> David Pommerenke
>>
>>
>>
>>-----Original Message-----
>>From: si-list-bounce@xxxxxxxxxxxxx on behalf of Doug Smith
>>Sent: Sun 9/3/2006 11:03 PM
>>To: SI-List; emc-pstc
>>Subject: [SI-LIST] Testing chips with system level specs
>>=3D20
>>Hi All,
>>
>>I have been writing and recording again, this time on applying
system=3D20
>>level ESD tests to devices. If you are involved with either =
devices=3D20
>>that can be handled by people (for instance a USB thumb drive for=3D20
>>flash memory card) or the equipment they plug into you will find =
my=3D20
>>latest article and podcast of interest. Any standards people out =3D
there?
>>
>>This month's Technical Tidbit describes a method to simulate air=3D20
>>discharges at voltages above 4 kV in a repeatable way using a modified
=3D
>>contact discharge. This method is especially useful in ESD testing
of=3D20
>>solid state circuits using IEC 61000-4-2.
>>
>>Abstract: Contact discharge is used in ESD testing to improve =
test=3D20
>>repeatability, yet air discharge has significantly different=3D20
>>characteristics at higher voltages. A test method is described =
that=3D20
>>uses a modified contact discharge to simulate the characteristics
of=3D20
>>an air discharge but with improved repeatability.
>>
>>The link to the article is the picture of the experimental test
setup=3D20
>>at the bottom of the home page at http://emcesd.com . Or just click on
=3D
>>this link:
>>
>>http://emcesd.com/tt2006/tt090106.htm
>>
>>There is also an audio discussion of this article on my podcast
site:=3D20
>>http://emcesd-podcast.com where the direct link to the audio file is:
>>
>>http://emcesd-podcast.com/2006/september/2006-0904.mp3
>>
>>Can't download mp3 files? Download the following instead:
>>
>>http://emcesd-podcast.com/2006/september/2006-0904.dcs
>>
>>After download, change the extension from .dcs to .mp3 and the =
file=3D20
>>will then be able to play on most computers.
>>
>>Doug
>>
>=3D20
>=3D20
--=3D20
------------------------------------------------------------
___ _ Doug Smith
\ / ) P.O. Box 1457
=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D Los =
Gatos, CA =3D
95031-1457
_ / \ / \ _ TEL/FAX: 408-356-4186/358-3799
/ /\ \ ] / /\ \ Mobile: 408-858-4528
| q-----( ) | o | Email: doug@xxxxxxxxxx
\ _ / ] \ _ / Web: http://www.dsmith.org
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