explain esd
Hi zhonghan,
So in reality there is not much to go on here. The image is from an old Zapmaster it looks like.
The green line is the pre-ESD-stressed curve trace showing that before ESD testing, pin 1 had a very strong forward biased diode (with Vt= ~0.7V) to a reference node for positive voltages, (if the reference node was pin 2, nothing in the schematic accounts for the strong diode...so I am wondering if there are some parasitic junctions related to the devices that are not explained by the schematic.)
...and a very resistive, possibly series diode path to the reference node for negative voltages.
What pin was used as reference for the curve trace...it may not have been pin 2.
The red curve is a curve trace post-ESD-stress, and shows a resistive fail (but you do not specify if your curve trace was between pin1 and 2 or pin 1 and some other ground...that matters too because it tells us to what node is pin 1 shorted...and its definitely shorted to something.
Other than that your pic doesn't tell much (other than pre and post stress curves...but nothing about what happened during the failure) and the schematic is not as useful without more understanding of the process.
I would suggest TLP to study the failure, FA if possible and also you need to take a hard look at both the parasitic junctions of the devices connected between pin 1 and 2 as well as who is shorted to Pin 1 as shown by the red line (in other words what pin was used as the reference for curve tracing pin 1...remember it may not have been pin 2).
This would be a start.
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