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ANSI/ESD S20.20- 2021 12 (This annex is no t part of ESD Asso ciation Standard ANSI/ESD S20.20- 2021 ) ANNEX B (INFOR MATIVE) – ESD SENSITI VITY TESTING Assessing t he ESD sensi tivity of parts , assem blies , a nd e qui…

ANSI/ESD S20.20-2021

(This annex is not part of ESD Association Standard ANSI/ESD S20.20-2021)

ANNEX A (INFORMATIVE) – ADDITIONAL PROCESS CONSIDERATIONS

The following sections provide guidance and outline documents available to help the users evaluate

additional control products and equipment. Users need to develop their acceptance and compliance

verification criteria as the industry has not yet defined the required limits for these items.

1. Automated Handlers (ANSI/ESD SP10.1, Automated Handling Equipment [AHE]). To

demonstrate ESD control in automated handling equipment, it may be necessary to measure

resistance to ground of machine components and monitor or verify electrostatic charge on a

product as it passes through the equipment. This can provide both continuous verification of

ESD countermeasures and a method for locating sources of charge generation. This standard

practice covers resistance-to-ground of machine components and sources of charge in

automated handling equipment. For more information on assessing equipment and processes,

see ANSI/ESD SP17.1, Process Assessment Techniques.

2. Gloves (ANSI/ESD STM15.1, Standard Test Method for In-Use Resistance Testing of Gloves

and Finger Cots). This standard test method is intended to provide test procedures for

measuring the intrinsic electrical resistance of gloves and finger cots and electrical resistance

of gloves or finger cots and personnel together as a system. This standard test method applies

to all gloves and finger cots used to control ESD. This standard test method provides data that

is relevant to the user's specific environment and application.

3. Conveyor systems often move unprotected ESD-sensitive items from station to station or

through various process stages such as surface mount technology (SMT) lines, wave solder

machines, and reflow ovens. Currently, no standard exists that addresses the various types of

conveyor systems. Some of the more common systems are flat belt systems, narrow belt

systems (often seen on SMT equipment), roller systems, and brush driven systems. While the

single flat belt systems can often use the same test methods as worksurfaces, the other

systems require different evaluation techniques.

4. ESD Handbook (ESD TR20.20). The ESD Association Standards Committee produced the

ESD Handbook for individuals and organizations faced with controlling ESD. It provides

guidance that can be used for developing, implementing, and monitoring an electrostatic

discharge control program per ANSI/ESD S20.20. This Handbook applies to activities that

manufacture, process, assemble, install, package, label, service, test, inspect, or otherwise

handle electrical or electronic parts, assemblies, and equipment susceptible to damage by

electrostatic discharges greater than or equal to 100 volts human body model (HBM). Charged

device model (CDM) and machine model (MM) factory issues are also addressed.

ANSI/ESD S20.20-2021

(This annex is not part of ESD Association Standard ANSI/ESD S20.20-2021)

ANNEX B (INFORMATIVE) – ESD SENSITIVITY TESTING

Assessing the ESD sensitivity of parts, assemblies, and equipment and the required protection

levels is an important element of an ESD control program. A common method for establishing ESD

sensitivity limits is to use HBM and CDM to characterize electronic items. The selection of specific

ESD control procedures or materials is at the discretion of the ESD control program plan preparer.

It should be based on risk assessment and the established ESD sensitivities of parts, assemblies,

and equipment. All devices should be considered sensitive to HBM and CDM.

Technical literature and failure analysis data exist that indicate ESD failures are due to a complex

series of interrelated effects. Some of the factors that influence ESD sensitivity include the ESD

current and energy envelope, the rise time of the ESD event, device design, fabrication technology,

and device package style. Energy sensitive devices are typically damaged by currents across a

circuit element or a protection element causing thermal damage. Voltage sensitive devices are

typically damaged when the breakdown voltage across a dielectric, for example, the gate oxide, is

exceeded. ESD sensitivity testing of devices, whether performed using HBM or CDM, provides

ESD sensitivity levels for comparing one device to another using defined parameters. The ESD

sensitivity of the device (defined in volts), as determined by using any of the defined models, may

not be the actual failure voltage level in the manufacturing process or user environment. Table 5

provides a reference for various standards and test methods for ESD sensitivity testing.

1. Human Body Model Sensitivity

A source of ESD damage is the charged human body, as modeled by HBM standards. This testing

model represents the discharge from the fingertip of a standing individual delivered to the

conductive contact of the device, for example, a conductive lead or a ball that is on a different

potential on at least one other conductive contact. It is modeled by a 100-pF capacitor discharged

through a switching component and 1500-ohm series resistor into the device under test (DUT).

HBM ESD sensitivity of devices may be determined by testing the device using one of the

referenced test methods.

2. Charged Device Model Sensitivity

A source of damage for CDM is the rapid discharge from a charged device to a conductive object.

The ESD event is device-dependent, but its location relative to ground can influence the failure

level in the real world. This test model assumes the device itself has become charged, and rapid

discharge occurs when the charged device's conductive leads contact a conductive surface, which

is at a lower potential. The entire CDM event can take place in less than 2.0 ns. Although very short

in duration, current levels can reach several tens of amperes during discharge. CDM ESD

sensitivity of devices may be determined by testing the device using the referenced test method.

3. Machine Model (Historical Information Only)

The MM was originally thought to describe a rapid transfer of energy to the conductive leads of the

device from an isolated charged conductor with at least one lead of the device grounded. The

equipment designed did not simulate the intended discharge event. Isolated charged conductor

discharges to devices that are not grounded can also be characterized by the CDM event. MM is

no longer required for device qualification as it does not give any additional information to the HBM

and CDM data. Nevertheless, the control of discharges from charged conductors in the

manufacturing environment is still a key element in the ESD control program. For more information

on MM, see JEDEC JEP172A: Discontinuing Use of the Machine Model for Device ESD

Qualification.

ANSI/ESD S20.20-2021

Table 5. ESD Susceptibility Test References for Devices

ESD Model

ESD Standards and Methods for Susceptibility Testing of Devices

HBM

ANSI/ESDA/JEDEC JS-001

MIL-STD-883-3 Method 3015

MIL-STD-750 Method 1020

MIL-PRF-19500

MIL-PRF-38534

MIL-PRF-38535

CDM

ANSI/ESDA/JEDEC JS-002

(For Information Only)

ESD SP5.2