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ANSI/ESD S20. 20- 2021 15 Technical Rationale for Deviation : Th e ESD sensitivity of waf ers in front- end manufacturi ng operations is significantly l ower than after the die are separated. A ceiling -bas ed room i oni…

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.

ANSI/ESD S20.20-2021

Technical Rationale for Deviation: The ESD sensitivity of wafers in front-end manufacturing

operations is significantly lower than after the die are separated. A ceiling-based room ionization

system is used in the EPA's covered in this ESD Control Plan. The purpose of this system is

primarily for contamination control. It will be utilized for reducing the charge on the many process

essential insulators typically present in any wafer fabrication facility. A wide-coverage (versus point-

of-use) ionization system is critical in any wafer fabrication facility to reduce electric fields on the

many process essential insulators. In limited critical operations where a tighter offset is deemed

required by engineering or the ESD program manager, peak ionizer offset voltage maximum

specification is ± 35 Volts.

Examples of Unacceptable or Unnecessary Tailoring Statements and Rationale

Example 1

Tailoring Statement: Seating as an ESD control item is not required because all personnel must

wear a grounded wrist strap when seated inside an EPA.

ANSI/ESD S20.20 Requirement Affected: Section 8.2 (personnel grounding), second paragraph:

"When personnel are seated at ESD protective workstations, they shall be connected to the

selected grounding / equipotential bonding system via a wrist strap system."

Why is this Tailoring Statement Unnecessary? The standard does not require ESD protective

seating. ESD protective seating is one of many 'optional' ESD control items for EPAs provided in

Table 3 of the standard. The actual requirement is for seated personnel to be connected to a

grounded wrist strap, and this is independent of whether ESD protective seating is used.

Example 2

Tailoring Statement: Nonessential insulators are not allowed inside the organization's EPAs in

designated areas.

ANSI/ESD S20.20 Requirement Affected: Section 8.3.1 (insulators), first paragraph, second

sentence: "All nonessential insulators shall be separated from any ESDS item by at least 300 mm".

Why is this Tailoring Statement Unnecessary? By not allowing nonessential insulators inside

EPAs, the ANSI/ESD S20.20 requirement to ensure all nonessential insulators are separated from

ESDS items by 300 mm is met. As a result, no tailoring statement is required.

Example 3

Tailoring Statement: The lower point to ground limit for worksurfaces used within the EPAs is

greater than 1.0 x 10

ohms instead of 0 ohms as required.

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

verification 'point to groundable point' and 'point to ground' minimum resistance limit of 0 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 Table 3

shall be met.

Why is this Tailoring Statement Unnecessary? The lower limit established is within the limits of

ANSI/ESD S20.20. Since it is within the limits, tailoring is not required. This lower limit will be the

requirement of this facility.

ANSI/ESD S20.20-2021

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

ANNEX D (INFORMATIVE) – RELATED DOCUMENTS

The following documents are listed for further reference. Some documents may be canceled.

However, this listing provides a reference of documents reviewed during the preparation of this

standard.

Military / U.S. Government

MIL-STD-3010, Federal Test Method Standard

MIL-PRF-81705, Barrier Materials, Flexible, Electrostatic Discharge Protective, Heat-Sealable

MIL-PRF-38534, Performance Specification: Hybrid Microcircuits, General Specification

MIL-PRF-38535, Performance Specification: Integrated Circuits (Microcircuits) Manufacturing,

General Specification

MIL-STD-883-3 Method 3015, Test method standard for microcircuits

MIL-STD-750-1 Method 1020, Test methods for semiconductor devices

MIL-PRF-19500, Semiconductor Devices, General Specification

MIL-STD-1686, Electrostatic Discharge Control Program for Protection of Electrical and Electronic

Parts, Assemblies and Equipment (Excluding Electrically Initiated Explosive Devices) – This

standard has been canceled.

MIL-HDBK-263, Electrostatic Discharge Control Handbook for Protection of Electrical and

Electronic Parts, Assemblies, and Equipment (Excluding Electrically-Initiated Explosive Devices) –

This handbook has been canceled.

MIL-M-38510, General Specification for Military Microcircuits - This standard is inactive.

MIL-DTL-82646, Plastic Film, Conductive, Heat Sealable, Flexible

MIL-PRF-87893, Workstations, Electrostatic Discharge (ESD) Control

MIL-STD-129, Marking for Shipment and Storage

MIL-STD-1285, Marking of Electrical and Electronic Parts

KSC-MMA-1985-79, Standard Test Method for Evaluating Triboelectric Charge Generation and

Decay

MIL-HDBK-103, List of Standard Microcircuit Drawings

Supplemental Information Sheet for Electronic QML-19500

Industry Standards

ANSI/IEEE-STD-142, IEEE Green Book (IEEE Recommended Practice for Grounding of Industrial

and Commercial Power Systems)

ANSI/ESD SP5.0, ESD Association Standard Practice for Electrostatic Discharge Sensitivity

Testing – Reporting ESD Withstand Levels on Datasheets

ANSI/ESDA/JEDEC JS-001, ESDA/JEDEC Joint Standard for Electrostatic Discharge Sensitivity

Testing – Human Body Model (HBM) – Component Level

ANSI/ESDA/JEDEC JS-002, ESDA/JEDEC Joint Standard for Electrostatic Discharge Sensitivity

Testing – Charged Device Model (CDM) – Device Level

ESD SP5.2, ESD Association Standard Practice for Electrostatic Discharge Sensitivity Testing -

Machine Model (MM) – Component Level

ANSI/ESD SP10.1, ESD Association Standard Practice for the Protection of Electrostatic

Discharge Susceptible Items – Automated Handling Equipment (AHE)

ANSI/ESD STM15.1, ESD Association Standard Test Method for the Protection of Electrostatic

Discharge Susceptible Items – Methods for Resistance Measurement of Gloves and Finger Cots