FAILURE MODES

Five ways to die

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🕳️

A hole burned through the dielectric, usually at a weak spot

🫧

Discharges in voids slowly eat the film

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Cracked end spray or leads: rising ESR and heat

Plus two more: leaks and swelling in oil-filled cans, and capacitance loss as metallized parts self-heal again and again.

Each failure mode leaves its own clues, which is what makes failure analysis possible.

GAME

Name the failure

Read the clues and pick the most likely failure mechanism.

Good failure analysis separates what you confirmed from what you suspect.

FAILURE ANALYSIS

🔎

Record as found Photos, markings and test history before anything changes

Electrical tests Capacitance, DF, insulation resistance, and hipot if safe

Look inside X-ray or CT for internal damage, then open the can

Unwind Unroll the section and find the puncture under a microscope

Tie it back Match the finding to lot records: film lot, winder, dry cycle

The goal isn't just to say why this part failed, but what to change so the next one doesn't.

WHEN FAILURES HAPPEN

🛁

Infant mortality Early failures from built-in defects; hipot and burn-in screen these out

Useful life A low, roughly flat rate of random failures

Wear-out Failures climb as the dielectric ages; life tests find where this starts

Screening tests trim the front of the bathtub; good design pushes the back wall further out.

SAFETY

⚠️

Lethal energy A charged high-voltage capacitor can kill, even unplugged

Discharge first Use a grounding stick or discharge resistor before touching

Dielectric absorption A discharged capacitor can recover a dangerous voltage on its own

Keep them shorted Parts are stored and shipped with shorting wires or bars across the terminals

Treat every high-voltage capacitor as charged until you've proven otherwise.

UNIT 13 STUDY COMPLETE

🔎

You've seen how capacitors fail, how failures are traced to causes, and how to handle stored charge safely.