Q.Capacitor guide of ESD (3): What are the ESD models?

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A. There are several ESD models including charged device model (CDM), machine model (MM), and human body model (HBM). Of these, the HBM is most commonly used to test and rate capacitors.

1. The CDM is one of the most neglected models. This ESD event occurs when a device slides down a tube, bag, or similar source. This also can occur when connecting the device to a ground. A common discharge network consists of a 4 or 30pF capacitor.
2. MM: Similar to the HMB is the Machine Model. This model originated in Japan as a worst case HBM. The Machine Model simulates a discharge from some conductive material such as a metal frame or tool. An example of this can be found in the pins of an automatic tester. A common discharge network consists of 200pF capacitor, no resistor, and discharging through a 500nH series inductor.
3. The HBM is the oldest and most common form of ESD. As stated in Mil-Std 1686 section 5.2.1.1, the principal source of ESD damage is the human body, as modeled by the HBM standards. Although this is called the human body model, it really represents the discharge from the human body or any charged device into an ESD sensitive (ESDS) device. This is commonly represented as the discharge from a fingertip to the device.

The equivalent circuit as shown here contains a charged capacitor Co. When the switch is thrown, Co discharges through Rx into the Capacitor (Cx).

This model was introduced under MIL-STD 883 method 3015 where Co = 100pF and RX = 1.5kohm. Also commonly used is IEC 61000-4-2 where Co = 150pF and RX = 330 ohms. For AEC-Q200, Co = 150pF and RX = 2kohm. In addition to these, there are countless variations of the HBM ESD test.

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