ANSI ESD-S20.20-2021-EN.pdf - 第21页

ANSI/ESD S20. 20- 2021 13 Table 5. ESD Susc eptibility Test Refere nces fo r Devices ESD Model ESD Standards and Methods for Suscept ibility Testing of Devices HBM ANSI/ESDA/JEDEC J S- 001 MIL -STD-883-3 Method 3015 MIL …

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

ANSI/ESD S20.20-2021

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

ANNEX C (INFORMATIVE) – TAILORING

Tailoring allows users of ANSI/ESD S20.20 to deviate from or exclude a requirement of the

standard if the user can provide justification and technical rationale for the deviation or exclusion.

Tailoring statements must be documented but are typically added to an organization's ESD control

program plan and include the requirement(s) of ANSI/ESD S20.20 that are excluded or modified

as well as the technical justification or rationale for the change.

The use of tailoring statements by an organization to deviate from or exclude a requirement from

ANSI/ESD S20.20 in an ESD control program plan is often misunderstood by both the organization

and those trying to determine compliance with the standard. This most often evolves from a

misunderstanding of what is or is not a requirement within the standard. In the tailoring examples

provided below, the affected requirement within ANSI/ESD S20.20 includes the word 'shall' or

'mandatory". Tailoring statements derived by the organization to address where and how the

program deviates from ANSI/ESD S20.20 requirements (see Section 6.3) must include the

requirement within the standard that is affected and the technical rationale for the exclusion or

deviation from the requirement.

Examples of Acceptable Tailoring Statements and Rationale

Example 1

Tailoring Statement: This ESD control program plan does not include personnel grounding.

ANSI/ESD S20.20 Requirement Affected: Section 8.2, first sentence: "All personnel shall be

bonded or electrically connected to the selected grounding/equipotential bonding system when

handling ESDS items."

Technical Rationale for Exclusion: The organization utilizes a fully automated manufacturing

process with no human interaction or handling of ESDS items.

Example 2

Tailoring Statement: The upper point to ground limit for worksurfaces used within cleanroom

EPAs is less than 1.0 x 10

ohms instead of 1.0 x 10

ohms as required for product qualification

and compliance verification.

ANSI/ESD S20.20 Requirement Affected: Table 3, product qualification and compliance

verification 'point to groundable point' and 'point to ground' maximum resistance limit of

1.0 x 10

ohms as tested using ANSI/ESD STM4.1 and ESD TR53, respectively. Also, in

Sections 7.3 (product qualification plan) and 7.4 (compliance verification plan), the required test

limits provided in Tables 2, 3, and 4 shall be met.

Technical Rationale for Deviation: The organization has a cleanliness requirement for multiple

cleanrooms where ESDS items are handled. The worksurface materials meeting cleanliness

requirements within these cleanrooms have resistance (point to ground) values that exceed

1.0 x 10

ohms but are less than 1.0 x 10

ohms. By ensuring these worksurfaces and personnel

are properly grounded, the organization believes all ESDS items and personnel are at the same

electrical potential. The manufacturing process in the cleanrooms where these worksurfaces are

used is controlled, and yield rates for the end products produced have been acceptable since the

initial installation.

Example 3

Tailoring Statement: The pulsed DC ceiling-mounted room ionization system utilized in this EPA

will have Offset Voltage (Peak): -250 volts < Voffset < 250 volts.

ANSI/ESD S20.20 Requirement Affected: Table 3, Product Qualification and Compliance

Verification Ionization Offset Voltage(Peak): -35 volts < Voffset < 35 volts.