Test Equipment

ESD Testing IEC 61000-4-2

ESD Background

Electrostatic Discharge (ESD) is the abrupt release of charge from one object (often a person) to another. Such a discharge can permanently damage or otherwise upset the function of sensitive electronic circuits.

Electronic products are tested for ESD immunity to insure their continued reliable operation if subjected to realistic levels of ESD after being placed in service. The European Union's EMC Directive mandates ESD immunity testing for virtually all electrical and/or electronic products as a condition for obtaining the CE Mark before shipping to a member state of the European Union.

Applicable Standards

Generic Immunity Standards, Product Standards and Product Family Standards require that ESD tests be performed in accordance with specific Basic EMC Standards: IEC 801-2, IEC 61000-4-2, or EN 61000-4-2. Application Note, EMC Standards Overview, provides an overview of European Standards for electromagnetic compatibility, describes how the Standards relate to one another, and lists sources for procuring copyrighted documents.

Basic EMC Standard

The Basic EMC Standards for ESD define methods of generating consistently reproducible electrical stresses for test purposes. They specify capacitances and resistances to model the human body's charge storing capability and discharge impedance, respectively. This model results in a current waveform, defined in the Standards. While the Basic EMC Standard also specifies how to perform ESD testing, the Generic, Product and Product Family Standards specify the test levels and pass/fail Performance Criteria.

Test Levels
 

 

Coupling Methods

Direct Coupling is a discharge directly to the Equipment Under Test (EUT), either in an Air Discharge mode, necessary for products having few or no metal surfaces, or via Contact mode, the preferred method. In the air discharge mode, the ESD event is initiated when the test simulator output is brought into close proximity with the EUT until a spark is initiated. The resulting stress is influenced by various environmental factors. In the preferred contact discharge mode, the test simulator output is first brought into physical contact with the EUT, then the ESD event is initiated under controlled conditions within the simulator.

Indirect Coupling simulates an ESD event which causes a radiated field to be emitted in the vicinity of the victim equipment. This is accomplished using Vertical Coupling Planes (VCP's) and Horizontal Coupling Planes (HCP's). Current standards require discharges be made to the edge of the VCP and surface of an HCP.

Waveforms

Waveform Verification

IEC 61000-4-2 requires the simulator output be verified periodically. A Model CTC-3 measurement target and target plane is required. The ESD current measurement is then made using a measurement system having a 1GHz or greater bandwidth. It is necessary to place the oscilloscope inside a shielded enclosure during the measurement to reduce the effects of radiated ESD directly to the measurement instrument.

Recent work by the Working Group 14.0 of the ESD Association has found that some simulators produce waveforms that are in compliance with IEC 61000-4-2, but have considerable ringing and high frequency components that do not show up with 1GHz instrumentation. These simulators may cause failures in products which would not occur if tested with a Thermo KeyTek simulator. Working Group 14.0 is preparing a document to describe waveform verification methods to allow manufacturers to verify the ESD current from simulators using high bandwidth instrumentation.

Number and Rate of Discharges

The manufacturer is required to develop a test plan identifying the EUT's most sensitive operating mode and appropriate test points. A minimum of 10 discharges are then made to each test point in either Contact Discharge or Air Discharge, according to the test plan. A recommended time interval of 1 second between tests should be used, but a longer interval is allowed if necessary to determine if a system failure has occurred.

For the indirect tests, 10 discharges are required to the Vertical Coupling Plane at each of 4 equipment faces (40 discharges) and then 10 discharges are required to the Horizontal Coupling Plane at 4 sides of the EUT (40 discharges).

EUT Performance Criteria

For ESD tests, the Generic Immunity Standards and Household Appliances Product Family Standard require that products operate as intended after the test. No degradation or loss of function is allowed below a performance level specified by the manufacturer. During the test, degradation is allowed, but not a change in the actual operating state or stored data. Refer to the tables located in the Generic, Product and Product Family Standards for specific Performance Criteria. The product cannot become unsafe under any conditions.

ESD Simulators

ESD Simulators meet all the simulator requirements of IEC 61000-4-2, including discharge network characteristics, discharge tips, and waveforms. Numerous accessories and discharge tips are available for those manufacturers requiring additional test capability and flexibility.