EOS failure of Power MOSFET

hexfet 1

Optical image of HEXFET® Power MOSFET.

hexfet 2

The breakdown site is located near the source wire bond.

hexfet 3

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 [1]. The breakdown current is estimated at ~ 1 amp/1 mil radius.

[1] 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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Black Pad Syndrome

BPS 1

BSE SEM image of BGA microsection.

BPS 2

The entire interface fractured between the Ni-Sn intermetallic layer and the Ni-P of the ENIG board pad. This is the corner ball where warpage strains are at maximum typically.

BPS 3

Evidence of “hyper-etching” of the Ni-P grain boundaries, which is a symptom of black-pad-syndrome.

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