Why can a Chip survive ESD but die instantly from EOS - Amazing

October 9, 2025

In the world of semiconductor and electronic design, the word “surge” is far from new. But have you ever wondered, why can a device pass an ESD (Electrostatic Discharge) test, yet still end up completely burned out by EOS (Electrical Overstress)?

Let’s explain these two long-time but often misunderstood “chip killers” in real engineering language.

ESD: The fast and precise natural assassin

ESD is a natural phenomenon caused by the discharge of static electricity accumulated on the human body or cables. When you plug or unplug a connector, touch a PCB, or even just change clothes, electric charge is already building up on you, ready to strike.

At the component level, there are three major ESD test models:

• HBM (Human Body Model): simulates human discharge, using a 100 pF capacitor and a 1.5 kΩ resistor.
• MM (Machine Model): simulates mechanical discharge, using a 200 pF capacitor and a 500 nH inductor.
• CDM (Charged Device Model): simulates the IC discharging itself.

At the system level, the IEC 61000-4-2 ESD gun model uses a 150 pF / 330 Ω network, which delivers about five times the energy of the HBM model. That means ESD happens within nanoseconds (ns), releasing amp-level current — an ultra-high-speed, high-frequency energy burst. The typical damage is a tiny pin-point burn at the bottom device layer, often visible only through delayering analysis.

EOS: The slow but ruthless human-made killer

Unlike ESD, EOS is a man-made phenomenon, usually caused by power-line surges, lightning induction, or poor grounding. Its discharge duration is in the microsecond (μs) range or longer, with energy levels thousands of times higher than ESD!

That means EOS doesn’t stab—it incinerates. In Decap or X-ray failure analysis, engineers often see blackened metal layers, melted bonding wires, or even charred packages.

The IEC 61000-4-5 standard defines EOS testing as:

• Voltage waveform: 1.2 / 50 μs
• Current waveform: 8 / 20 μs
• Internal discharge resistance: 2 Ω
• Capacitance: 5 μF (massive energy)

Networking and Industrial electronic products typically use the Thermo KeyTek EMCPro Plus (up to 6 kV) for EOS testing, while consumer electronics often use KAST KT200-SG from Korea or Prima TVS 8/20 from China.

ESD vs EOS - more than just energy

One of the most common design mistakes engineers make is choosing TVS diodes rated only for ESD, ignoring EOS protection. As a result, the IC passes the ESD qualification but still gets “one-shot killed” in the field by an AC-line surge or grounding fault.

Conclusion: The next-generation protection mindset

Future protection design cannot focus solely on static-discharge standards. It must meet both IEC 61000-4-2 (ESD) and IEC 61000-4-5 (EOS) requirements. Only TVS structures capable of providing nanosecond-level protection and microsecond-level endurance can ensure real-world system reliability.

So next time you see a TVS diode proudly labeled “IEC 61000-4-2 8 kV”, don’t forget to ask the key question:

“What’s its EOS capability under the 8/20 μs surge waveform?”

That single question could be the difference between a robust system, and a pile of burnt silicon.