Failure modes · Electronic

Power MOSFET — Failure Modes & Failure Rate

Voltage-controlled switching transistor dominant in modern power conversion. Failure rate driven by avalanche events, gate-oxide stress, and bond-wire fatigue from thermal cycling. The most common single failure point in motor drives and switch-mode supplies.

λ typical

2.0×10-8 / h

Range

5.0×10-9 – 1.0×10-7

Source

SN 29500-2 / IEC 62380

Failure modes

Drain-source short

Root causes: Avalanche event (V_DS exceeded, repetitive unclamped inductive switching); parasitic-BJT latch-up under high dV/dt; gate-oxide breakdown after long stress; thermal runaway during hard short-circuit fault.
Detection: Catastrophic supply-rail collapse; protective fuse opens; thermal damage visible on the package.
Mitigation: Avalanche-rated parts with sufficient EAS energy margin; gate-driver with controlled dV/dt; desat protection in IGBT-style applications; thermal interface and heatsinking sized for fault duration.

Open-circuit (bond-wire lift / package crack)

Root causes: Aluminium bond-wire fatigue under high ΔT thermal cycling (every on/off cycle stresses the wire); package delamination; corrosion in non-hermetic packages.
Detection: Loss of switching action; output stage stuck off; sometimes intermittent (cracked wire that reconnects when warm).
Mitigation: Limit junction-temperature swing per cycle (ΔT_j ≤ 60 °C target for long life); copper bond wires for high-cycling applications; package selection (TO-247 over TO-220) for high power density.

Gate-source short

Root causes: Gate-oxide breakdown from over-voltage transient on the gate driver; ESD during handling or service.
Detection: Gate-driver current draw goes high or driver pulled out of regulation; switch fails on or off depending on bias.
Mitigation: Zener clamp on the gate; gate-driver with active Miller clamp; ESD handling procedures during service.

Increased Rds(on)

Root causes: Gate-oxide trapping; metallisation reconstruction from current cycling.
Detection: Package temperature rises over service life for the same load; conduction loss measurable on the rail.
Mitigation: Derate continuous current to 60–70% of datasheet rating; monitor case temperature for predictive maintenance.

Typical applications

Switch-mode power-supply primary and synchronous-rectifier roles; motor-drive H-bridges and three-phase inverters; load switches; battery-protection FETs. Universal in any modern power-electronics design.

How to model in a fault tree

In a fault tree for a motor-drive function, each MOSFET in the bridge is its own basic event — don't aggregate across phases because failure modes (e.g. shorted high-side FET) have different system-level consequences. For ASIL-D propulsion inverters, layer Beta-CCF across the six bridge FETs since they share a gate-driver IC, gate-supply, and thermal path — a single gate-supply transient can take all six out simultaneously.