Dear Patric,
Thank you very much for your thorough look into the issue and for the
detialed explanations. Attaching a copper tape to the metal ring of the sensor
and applying contact ESD pulses to that copper tape is the recommendation from
the manufacturer too.
But as many others pointed, if contact discharge can damage the soft
sensor then the same damage can happen while user swipes his fingers on the
sensor. Do you accpet this or do you believe only if a metalic object like
weddign ring or car key or contact discharge tip comes into contact with the
soft sensor it will fail and the sensor will be able to withstand the finger
contact without any issues.
Bharath
From: "Conway, Patrick R (Houston)" <[email protected]>
To: "Pettit, Ghery" <[email protected]>; Philo Beddo
<[email protected]>; [email protected]
Sent: Friday, 9 November, 2007 2:28:25 AM
Subject: RE: CCD type sensor - ESD testing
The driving issue is the mechanical damage.
What if the contact discharge will cause damage to the EUT, and the EUT then
malfunctions? How does the lab engineer determine pass/fail if they cannot
distinguish an ESD failure from a mechanical failure?
My suggestions are intended to be practical suggestions on how to separate the
mechanical failures from the ESD failures.
Best Regards,
Patrick.
[email protected]
_____
From: Pettit, Ghery [mailto:[email protected]]
Sent: Thursday, November 08, 2007 2:52 PM
To: Conway, Patrick R (Houston); Philo Beddo; [email protected]
Subject: RE: CCD type sensor - ESD testing
Yes, but there is no need to perform the air discharge test to a conductive
surface according to CISPR 24. Contact discharge to conductive surfaces and
air discharge to insulated/non-conducting surfaces. This shouldn’t be an issue.
Ghery Pettit
_____
From: Conway, Patrick R (Houston) [mailto:[email protected]]
Sent: Thursday, November 08, 2007 12:14 PM
To: Pettit, Ghery; Philo Beddo; [email protected]
Subject: RE: CCD type sensor - ESD testing
I think your descriptions are accurate. However, it is still possible to
slightly modify the test description without changing the ESD result and still
avoid the damage. For instance, since the air discharge will happen before the
air gap = zero, then the approaching ESD gun can stop movement as soon as the
discharge happens. The modified process will still have the desired ESD
discharge, but will avoid the mechanical damage.
Best Regards,
Patrick.
[email protected]
_____
From: [email protected] [mailto:[email protected]] On Behalf Of Pettit, Ghery
Sent: Thursday, November 08, 2007 12:13 PM
To: Conway, Patrick R (Houston); Philo Beddo; [email protected]
Subject: RE: CCD type sensor - ESD testing
How is it that damage occurs with the contact discharge test method, but not
the air discharge method? In the contact discharge test the tip of the ESD gun
is brought into contact with the test point and the trigger is pulled, causing
the discharge to occur inside the gun, injecting the signal into the test
point. Contact may be made as gently as necessary. In the air discharge test
the trigger is pulled, charging the tip of the gun and the gun is brought into
contact with the EUT with the discharge occurring sometime before the tip comes
smashing into the test point. It seems to me that contact discharge, which is
the required technique when discharging to a conductive surface, is the less
damaging from a mechanical point of view.
Or am I missing something here?
Ghery Pettit
_____
From: [email protected] [mailto:[email protected]] On Behalf Of Conway, Patrick
R (Houston)
Sent: Thursday, November 08, 2007 8:32 AM
To: Philo Beddo; [email protected]
Subject: RE: CCD type sensor - ESD testing
I agree. The user accessible point in this discussion shall be subject to ESD
testing.
So the question is how to test- should it be contact (as prescribed in the
standard), or air?
Some thinking is required.
Each us may settle on a different answer, with each solution being
appropriate.
On this type of sensor, mechanical damage *will* occur if the contact
discharge tip comes into contact with it.
Same damage as if a user's wedding ring, or car keys or any such object
contacts the sensor.
So, if one follows the EN55024 standard for testing, and mechanical
damage occurs, how do you assess pass/fail?
How do you decide if the failure is due to ESD, or to mechanical
damage?
It is impossible to tell.
Ignoring for the moment the question of field returns and reliability
issues, how do we test to ensure that ESD performance is acceptable?
Two possible test solutions come to my mind.
I put them out for consideration and discussion:
a) waive the contact discharge requirement since damage occurs.
execute air discharge only- but increase the pass/fail limit to
account for differences in test method.
b) add a small piece of Cu tape to the EUT,
make contact between the soft sensor and some point where the
contact tip can make contact.
allow the contact tip to press the Cu tape, conducting the
transient to the sensor surface.
once again- increase the pass/fail voltage level to account for
test differences.
Thoughts? Comments?
Best Regards,
Patrick.
[email protected]
_____
From: [email protected] [mailto:[email protected]] On Behalf Of Philo Beddo
Sent: Wednesday, November 07, 2007 6:32 PM
To: [email protected]
Subject: RE: CCD type sensor - ESD testing
All,
despite reading many descriptions of ESD testing, one thing keeps jumping out
at me.
The "test point" in question is both operator accessible AND the operator is
directed to touch the point in question.
I'm paraphrasing:
Per EN61000-4-2...operator accessible areas are to be tested
Per EN55024 (though I don't know much about the product): areas in which the
operator is directed to have contact with are test points.
Sounds like this "test point" should be evaluated.
Simply:
if the surface is conductive....using contact discharge
if the surface is non-conductive/ insulating....using air discharge
Ash.
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