2. Insights…
• Why ESD is the problem…?
• When spark happens…?
• Evaluation of ESD…
• Real life ESD…
• Contact discharge setup…
• References…
3. Why ESD is the problem…?
• We give a shock to the device (2kV to 25kV)
4. Cont…
• Affects all the sensitive components…
• E.g., Microprocessor and IC’s
• Trace width is in milli/micro/nano for semiconductor
devices hence the more current can burn the traces
• Resets the device functions
• IC’s have reset or Interrupt function when we apply ESD (trigger) It resets the
device
5. When spark happens…?
• The effect of lightning
needs 3million V/m
(Air dielectric breakdown)
So,
• ESD requires 3kV/mm
to create the spark…!
6. Evaluation of ESD…
• From a physics view human is an ESD gun…!
150pF
150pF
330 ohms
2k ohms
When we hold a key we allow the
charges to flow faster
Effective resistance is 330 ohms
approx.
When we touch any components
directly the charges take some
time to ground
Effective resistance is 2k ohms
(dry skin) approx.
7. Cont…
• Capacitance of a sphere
• 𝑐 = 4𝜋𝜀𝑎
• C=111*a*10^-12
• C=111*a pF
• where ‘a’ is in meter
• Approximately human body surface is equivalent to 0.5m radius of a sphere
• C= 111*0.5 ≈ 50pF approximately
a
a
The capacitance between foot to the ground and the
adjacent objects plays the main role
When we stand on floor we makes 150pF approximately
but inside the car it much more. Approximately
Technical committee of IEC/ISO may find that to be 330pF
Thanks to Dr. Bogdan Adamczyk (Reference)
8. Cont…
Inside the car Outside the car
Key touch
Finger touch
330pF 330 Ω 150pF 330 Ω
330pF 2kΩ 150pF 2kΩ
9. Cont…
• The RC network selection is based on the DUT where we are going to place
inside the car
• When we have no idea about the DUT placement (ex. Prototype) It’s best to
test with 330pF|330 Ω network
• When the DUT is accessible from inside and outside of a car 150pF and 330pF
networks are used for the testing
• Metal body of the DUT is tested under Contact discharge
• Insulating part is tested under Air discharge
10. Real life ESD…
• In a real life scenario we can’t create contact discharge…!
• Still we are doing contact discharge…!
• It’s really tough to achieve the repeaable results by air discharge
The charges will conduct through the air (by dielectric breakdown) before we touch the DUT
The smallest human made lightning…!
The reason is to achieve the repeatability and reproducibility
Air discharge is only repeatable when we achieve the same…
1. The approaching speed of ESD gun to the DUT
2. Distance between gun tip to the DUT
3. Humidity is also a reason
Finally we don’t
want to spend
too much time for
the repeatability
11. Cont…
• Contact discharge tests the grounding quality of the DUT by passing
the charges towards the ground
• Air discharge tests the quality of the insulator by the air dielectric
breakdown
• Indirect coupling tests the worst coupling characteristics of the DUT
by applying the fields over the DUT
• Package and handling test (un powered)is a very unique test only
meant for Automotive domain.
ESD test is the combination of conducted and radiated Immunity test
This is gateway to the remaining tests.
It’s like crossing the half ocean once the DUT passes in ESD test…!
Field coupling method is
the best way to achieve
the more repeatability and
it simulates the real
vehicle condition too…
12. Contact discharge Setup…
100mm
5mm thickness of
styrofoam
Typical spacing between the accessories is 200mm
Battery negative
to the ground plan
Return cable to the DUT should be more than 200mm
13. Food for thoughts…
• Why does ESD gun have sharp pointer for Contact discharge and ball
pointer for Air discharge…?
vs
Charges reassemble themselves to achieve a
steady state(equilibrium)
When we through a bunch of charges to a
conductor the charges will repel each other and it
tries to move the farthest distance each other…!
Charges wont distribute itself equally…!
It always pushes each other away…!
Our aim is to apply all the charges over the device by contact discharge.
So when we have a sharp pointer we can see the more charges on the tip pointer.
Once the pointer touches the metal surface all the charges are so happy to escape
from the stressful environment
When we even don’t touch the metal by the sharp pointer the charges will ionize through the air (the
bluish color on the tip called corona discharge)
You can think of
the same with the
ball pointer tip…!
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