Human Body Model 100pF ESD Strike Simulation on Connector Pins

This article explains how the Human Body Model (HBM) simulates an electrostatic discharge (ESD) event onto external connector pins in electronic devices. By using a standardized circuit consisting of a 100-picofarad (100pF) capacitor and a 1,500-ohm resistor, engineers can replicate the static electricity transferred from a person's fingertip to sensitive electronic components. The following sections break down the mechanics of the circuit, the test setup, the resulting discharge waveform, and how this simulation helps design robust protection for external interfaces.

The Core Components of the HBM Circuit

To accurately simulate a human touching an electronic connector, the HBM uses a simplified electrical network defined by standards such as JEDEC JS-001 and MIL-STD-883. The circuit relies on three main elements:

  • High-Voltage Power Supply: Charges the system to a predetermined voltage level, typically ranging from 500 volts to 8,000 volts, representing the static buildup on a person.
  • 100-Picofarad (100pF) Capacitor: Represents the electrical capacitance of an average standing human body. It stores the electrostatic charge before the strike occurs.
  • 1,500-Ohm Resistor: Represents the electrical resistance of human skin and body tissue. It limits the current and dictates the decay rate of the electrical pulse during the discharge.

The Charging and Discharging Process

The simulation occurs in two distinct phases controlled by a high-voltage relay switch.

First, the relay connects the 100pF capacitor to the high-voltage power supply. The capacitor charges until it reaches the specified test voltage. This mimics a person accumulating static charge by walking across a carpet or sliding out of a car seat.

Second, the relay switches positions, disconnecting the power supply and connecting the charged 100pF capacitor directly in series with the 1,500-ohm resistor. The other end of the resistor is connected directly to the external connector pin of the device under test (DUT). The stored energy dumps rapidly through the resistor and into the connector pin, simulating the exact moment a finger makes contact with the metal interface.

The HBM Current Waveform

When the 100pF capacitor discharges through the 1,500-ohm resistor into a low-impedance connector pin, it produces a specific current waveform. This standardization ensures that tests are repeatable across different laboratories.

  • Rise Time: The current spikes rapidly, reaching its peak in 2 to 10 nanoseconds. This simulates the fast arc of electricity jumping from a finger to the metal pin.
  • Peak Current: For a standard 2,000-volt (2kV) HBM test, the peak current reaches approximately 1.33 amps (calculated roughly by dividing the 2,000V charge by the 1,500-ohm resistance).
  • Decay Time: As the 100pF capacitor depletes its stored energy through the resistor, the current exponentially decays. The total duration of the pulse lasts around 150 nanoseconds.

Testing External Connector Pins

External connector pins—such as USB ports, HDMI interfaces, and power jacks—are the primary entry points for ESD strikes in real-world applications. To test these pins using the HBM simulation, engineers use specialized automated test equipment (ATE).

  1. Pin Grounding: One or more ground pins on the device are connected to the return path of the HBM tester.
  2. Pin Stressing: The test probe contacts the specific external connector pin being evaluated.
  3. Polarity Testing: The 100pF capacitor applies both positive and negative voltage strikes to the pin, as static charge on a human can be of either polarity.
  4. Failure Analysis: After the strikes are delivered, the device is tested for functionality and leakage current. If the internal silicon has melted or the insulating oxide layers have punctured, the pin fails the HBM qualification.

HBM vs. System-Level Testing on External Pins

While the 100pF and 1,500-ohm HBM circuit is the industry standard for testing individual integrated circuits (ICs) in a factory environment, external connector pins on finished products often face harsher conditions.

Because external pins are exposed to the outside world, engineers also subject them to the IEC 61000-4-2 standard. The IEC model uses a larger 150pF capacitor and a much lower 330-ohm resistor to simulate a person holding a metal object (like a key or cable) discharging into a port. However, the 100pF HBM simulation remains the foundational benchmark for determining the baseline survival threshold of the silicon chips wired directly behind those external connector pins.