Optical image of HEXFET® Power MOSFET.
The breakdown site is located near the source wire bond.
This is a higher magnification image of the breakdown site.
The breakdown current in amperes can be roughly estimated by the radius of the “hot spot” or breakdown site . The breakdown current is estimated at ~ 1 amp/1 mil radius.
 J. T. May, “Limiting Phenomena in Power Transistors and the Interpretation of EOS Damage”, in Microelectronics Failure Analysis Desk Reference, 3rd Edition, ASM International Press, 1993, pp. 321-328.
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