Lesson 3/1030%
MODULE 03

ESD Models: HBM, MM & CDM

Real ESD events don't all look alike. Standards bodies capture the range of real-world events with three idealized discharge models, each with a different equivalent circuit, energy, and current waveform — and each relevant to a different point in a product's life.

Learning Objectives

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Describe the Human Body Model (HBM)
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Describe the Machine Model (MM)
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Describe the Charged Device Model (CDM)
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Compare their waveforms and applicability

Every discharge model reduces a messy real-world event to a simple RC (or pure capacitive) equivalent circuit that a test generator can reproduce consistently. Select a model to see its circuit and characteristics.

Yellow circular ESD susceptibility symbol showing a crossed-out hand reaching for a triangle
The ESD susceptibility symbol (ANSI/ESD S8.1). Any part or assembly marked with it is HBM/CDM-sensitive and must only be handled at a protected workstation.
Gloved hand wearing a grounded ESD wrist strap with coiled cord
The Human Body Model exists because of exactly this scenario: a grounded wrist strap continuously drains body charge (through a 1 MΩ safety resistor) so it can never reach a device pin.

Animated: Equivalent Circuit & Discharge Path

Parameter HBM MM CDM
Equivalent circuit 100 pF + 1.5 kO series R 200 pF, ~0 O (no series R) Device self-capacitance, no series R
Charge source A charged person A charged tool, cart, or fixture The device itself, charged then grounded
Rise time ~2-10 ns ~a few ns, oscillatory Sub-nanosecond, extremely fast
Peak current (typical test level) ~1.3 A at 2 kV ~3-4 A at 200 V (oscillatory, can ring negative) Tens of amps in under a nanosecond
Typical relevance People handling boards/products Automated handling equipment (largely phased out of most modern component specs) Automated assembly, tape-and-reel, pick-and-place
Standard(s) ANSI/ESDA/JEDEC JS-001; IEC 61000-4-2 (system-level, different circuit) ANSI/ESDA/JEDEC JESD22-A115 (legacy) ANSI/ESDA/JEDEC JS-002
IEC 61000-4-2 (the focus of this course, covered in Module 04) is a system-level test with its own 150 pF / 330 O generator circuit -- similar in spirit to HBM but not identical, and calibrated to represent a person discharging directly into a finished product rather than a bare component on a test board.

Normalized current waveforms for each model, illustrating why CDM is the hardest to protect against: its rise time is far faster than HBM or MM, so on-chip protection has almost no time to react.

KNOWLEDGE CHECK

Module 3 Quiz

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