ANSI S20.20 ESD Standards

"In order to meet the global need in the electronics industry for technically sound ESD Control Programs, the ESD Association has established an independent third party certification program. The program is administered by the ESD Association through country-accredited ISO9000 Certification Bodies that have met the requirements of this program. The Facility Certification Program evaluates a facility's ESD program to ensure that the basic requirements from industry standards ANSI/ESD S20.20 or IEC 61340-5-1 are being followed. More than 384 facilities have been certified worldwide since inception of the program. The factory Certification Bodies report strong interest in Certification to S20.20, and consultants in this area report that inquiries for assistance remain at a very high level. Individual education also seems of interest once again as 46 professionals have obtained Certified ESD Program Manager status and many more are attempting to qualify as Certified ESD Control Program Managers. A large percentage of the certification program requirements are based on Standards and the other related documents produced by the ESD Association Standards Committee." - ESDA.ORG Standards Update 2011

Contents

Definitions

Examples of ESDS Items
Examples of ESDS items include microcircuits, discrete semiconductors, thick and thin film resistors, hybrid devices, printed circuit boards and piezoelectric crystals. It is possible to determine device and item susceptibility by exposing the device to simulated ESD events. The level of sensitivity, determined by testing using simulated ESD events, may not necessarily relate to the level of sensitivity in a real-to-life situation. However, the levels of sensitivity are used to establish a baseline of susceptibility data for comparison of devices with equivalent part numbers from different manufacturers. Two different models are used for characterization of electronic components: HBM and CDM.

Human body Model Sensitivity (HBM)
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 leads of the device. It is modeled by a 100 PF capacitor discharged through a switching component and 11500-ohm series resistor into the device under test. All devices should be considered as HBM sensitive. The HBM ESD sensitivity of devices may be determined by testing the device using one of the referenced test methods.

Charged Device Model Sensitivity (CDM)
A source of damage for the CDM is the rapid discharge of energy from a charged device. The ESD event is totally device dependent, but its location relative to a ground can influence the failure level in the real world. The assumption for this test model is that 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 nanoseconds. Although very short in duration, current levels can reach several tens of amperes during discharge.

Machine Model Sensitivity
A source of damage for the MM historically was described as a rapid transfer of energy to the conductive leads of the device. Isolated charged conductor discharges to devices are better 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 Machine Model and device targets, see A Case for Lowering Component Level HBWMM ESD Specifications and Requirements by the industry Council.

Industries and Activities

This document applies to activities that manufacture, process, assemble, install, package, label, service, test, inspect, transport or otherwise handle electrical or electronic parts, assemblies and equipment susceptible to damage by electrostatic discharges greater than or equal to 100 volts HBM, 200 volts CDM and 35 volts on isolated conductors. Activities that handle items that are susceptible to lower withstanding of voltages may require additional control elements or adjusted limits. Processes designed to handle items that have an ESD sensitivity to lower withstand voltages can still claim compliance with this standard. This document does not apply to electrically initiated explosive devices, flammable liquids or powders.

NOTE: The CDM voltage level as used in this document is based on managing process essential insulators to mitigate induced voltages on devices that could lead to damage.

NOTE: Isolated conductors were historically represented by MM.

Compliance for Grounding of Conductors and Non-Conductors

Grounding of Conductors
All conductors in the environment, including personnel, shall be bonded or electrically connected and attached to a known ground or contrived ground (as on shipboard or on aircraft). This attachment creates an equipotential balance between all items and personnel. Electrostatic protection can be maintained at a potential above a "zero" voltage ground potential as long as all items in the system are at the same potential.

Essential Non Conductors
Necessary non-conductors (i.e. process-required insulators) in the environment cannot lose their electrostatic charge by attachment to the ground. Ionization systems provide neutralization of charge on these necessary non-conductive items (circuit board materials and some device package are examples of necessary non-conductive items (circuit board materials and some device package are an example of necessary non-conductors). Assessment of the ESD hazard created by electrostatic charge on the necessary non-con conductors in the workplace is required to ensure that appropriate actions are implemented, commensurate with the risk to ESDS items.

SMT Carts

Transportation of ESDS Items
Transportation of ESDS items outside an ESD Protected Area (hereafter referred to EPA) requires enclosure in static protective materials, although the type of material depends on the situation and destination. Inside an EPA, low charging and static dissipative materials may provide adequate protection. Outside an EP, low charging and static discharge shielding materials are recommended. While these materials are not discussed in the document, it is important to recognize the differences in their application. For more clarification, see ANSI/ESD S541. Any relative motion and physical separation of materials or flow of solids, liquids or particle-laden gases can generate an electrostatic charge. Common sources of ESD include personnel, items made from common polymeric materials, and processing equipment. ESD damage can occur in a number of ways, including:

  1. A charged object (including a person) coming into contact with an ESDS item.
  2. A charged ESDS device making contact with a ground or another conductive object at a different potential
  3. An ESDS device is grounded while exposed to an electrostatic field.
8.1 Grounding | Equipotential Bonding Systems

Grounding / Equipotential Bonding Systems shall be used to ensure that ESDS items, personnel and any other conductors that come into contact with ESDS items (e.g., mobile equipment) are at the same electrical potential. An implementing process shall be selected from Table 1.

Table 1. Grounding / Equipotential Bonding Requirements

Technical Requirement Implementing Process Test Method Required Limit(s)
Grounding/Bonding Systems Equipment Grounding Conductor ANSI/ESD S6.1 < 1.0 ohm impedance
Auxillary Ground ANSI/ESD S6.1 < 25 ohms to the Equipment Grounding Conductor
Equipotential Bonding ANSI/ESD S6.1 < 1.0 x 109 ohms(3)
8.2 Personnel Grounding

Wrist Straps
All personnel shall be bonded or electrically connected to the grounding / equipotential bonding system when handling ESDS items. The personnel grounding method(s) shall be selected from Table 2. Personnel seated at ESD protective workstations shall be connected to the grounding / equipotential bonding system via a wrist strap. For standing operations, personnel shall be grounded via a wrist strap or by a footwear/flooring system meeting the requirements of Table 2.

Garments
When garments are used to achieve personnel grounding, it shall be documented in the ESD Control Program Plan. The garment shall have electrical continuity from one sleeve to the other and must also meet the wrist strap resistance requirements defined in Table 2 and the groundable static control garment system in Table 3.

Table 2. Personnel Grounding Requirement

Technical Requirement Product Qualification(4) Compliance Verification
Test Method(s) Required Limit(s) Test Method(s) Required Limit(s)
Wrist Strap System ANSI/ESD S1.1 (section 6.11) < 3.5 x 107 ohms ESD TR53 Wrist Strap Section < 3.5 x 107 ohms
Footwear / Flooring System5 (Both limits must be met) ANSI/ESD STM97.1 < 1.0 x 109 ohms ESD TR53 Footwear Section < 1.0 x 109 ohms(6)
ANSI/ESD STM97.2 < 100 volts Peak ESD TR53 Footwear Section < 1.0 x 109 ohms(6)

Table 3. EPA ESD Control Items

Technical Requirement ESD Control Item Product Qualification Compliance Verification
Test Method(s) Required Limit(s)8 Test Method(s) Required Limit(s)
EPA Worksurface(9,10) (Qualification can be done by either Test Method) ANSI/ESD S4.1 9 ohms ESS TR53 Worksurface Section Point to Ground < 1.0 x 109

Point to Groundable Point
< 1.0 x 109 ohms

< 200 volts

ANSI/ESD STM4.2
Wrist Strap ANSI/ESD S1.1 0.8 x 106 to 1.2 x 106 ohms For compliance verification of a Wrist Strap System, see Table 2.
Wristband ANSI/ESD S1.1 Interior
1.0 x 105 ohms
Exterior
1.0 x 107 ohms
Personnel Ground Wrist Strap Connection (non-monitored) ANSI/ESD S6.1 Point to Ground
< 2.0 ohms
ESD TR53 Grounding Bonding Systems Point to Ground
< 2.0 ohms
Footwear ANSI/ESD STM9.1 Point to Groundable Point
< 1.0 x 109 ohms
For compliance verification of a Footwear / Flooring System, see Table 2.
Foot Grounders ANSI/ESD SP9.2 Point to Groundable Point
< 1.0 x 109 ohms
Flooring ANSI/ESD STM7.1 Point to Point
< 1.0 x 109 ohms
Point to Groundable Point
< 1.0 x 109 ohms
Seating ANSI/ESD STM12.1 Point to Groundable Point
< 1.0 x 109 ohms
ESD TR53 Seating Section Point to Ground
< 1.0 x 109 ohms
Ionization ANSI/ESD STM3.1

Discharge Time
User defined

Offset Voltage
-35 < V offset < 35

Point to Point
< 1.0 x 109 ohms

ESD TR53(11) Ionization Section

Discharge Time
User defined

Offset Voltage
-35 < V offset < 35

Shelving
(When used to store unprotected ESDS)
ANSI/ESD S4.1 Point to Groundable Point
< 1.0 x 109 ohms
ESD TR53 Worksurface Section Point to Ground
< 1.0 x 109 ohms
Mobile Equipment (Working Surfaces) ANSI/ESD S4.1 Point to Point
< 1.0 x 109 ohms
ESD TR53 Worksurface Section Point to Ground
< 1.0 x 109 ohms
Point to Groundable Point
< 1.0 x 109 ohms
Electrical Soldering / Desoldering Hand Tools ANSI/ESD S13.1 Tip to Ground or Groundable Point
< 2.0 ohms
ESD TR53 Worksurface Section Tip to Ground or Groundable Point
< 10 ohms
Tip < 20 millivolts
Tip Leakage < 10 milliamps
Continuous Monitors User defined User defined ESD TR53 Continuous Monitors Section Manufacturer defined
Static Control Garment ANSI/ESD STM2.1 Point to Point
< 1.0 x 1011 ohms
ESD TR53 Garments Section Resistance Point to Point
< 1.0 x 1011 ohms
Groundable Static Control Garment ANSI/ESD STM2.1 Point to Groundable Point
< 1.0 x 109 ohms
ESD TR53 Garments Section Resistance to Groundable Point
< 1.0 x 109 ohms
Groundable Static Control Garment System ANSI/ESD STM2.1 < 3.5 x 107 ohms ESD TR53 Personal Grounding with Garments Section < 3.5 x 107 ohms
8.3 ESD Protected Areas (EPAs)

Handling of ESDS items, parts, assemblies, and equipment without ESD protective covering or packaging shall be performed while in an EPA. The EPA shall have clearly identified boundaries.

NOTE: An EPA can consist of a single workstation, entire room, building or other designated areas. Access to the EPA shall be limited to personnel who have completed appropriate ESD training, Untrained individuals shall be escorted by trained personnel while in an EPA. An EPA shall be established wherever ESDS items are handled. However, there are many different ways to establish ESD controls within an EPA. Table 3 lists some optional ESD control

Compliance For ESD Protected Areas
  1. The maximum resistance between any ESD control items and the common connection point.
  2. Product qualification is normally conducted during the initial selection of ESD control products and materials. Any of the following methods can be used, product specification review, independent laboratory evaluation or internal laboratory evaluation.
  3. For ESD control footwear monitoring systems that were installed before the adoption of this standard, ongoing compliance verification records can be used as evidence of product qualification.
  4. The required limit of < 1.0 x 109 ohms is the maximum allowed value. The user should document the resistance values that were measured for product qualification for the footwear and the floor to comply with the < 100 volts body voltage generation and use these resistances for compliance verification. items which can be used to control static electricity. For those ESD control items that are selected for use in the ESD Control Program, the required limits and test methods for those items become mandatory.
8.3.1 Insulators

All non-essential insulators such as coffee cups, food wrappers, and personal items shall be removed from the EPA. The ESD program shall include a plan for handling process-required insulators in order to mitigate field-induced CDM damage. If the field measured on the process required insulator is greater than 2000 volts/inch and the process required insulator is less than 30 cm (12") from the ESDS item, steps shall be taken to either:

  1. Separate the required insulator from the ESDS item by a distance of greater than 30 cm (12")
  2. Use ionization or other charge mitigating techniques to neutralize the charge.

If the field measured on the process required insulator is greater than 125 volts/inch and the process required insulator is less than 2.5 cm (1") from the ESDS item, steps shall be taken to either:

  1. Separate the required insulator from the ESDS item by a distance of greater than 2.5 cm (1")
  2. Use ionization or other charge mitigating techniques to neutralize the charge.

NOTE: The accurate measurement of electrostatic fields requires that the person making the measurement is familiar with the operation of the measuring equipment. Most hand-held meters require that the reading is recorded at a fixed distance from the object. They also normally specify that the object has a minimum dimension of fixed size in order to obtain an accurate reading.

8.3.2 Testing Isolated Conductors with a Voltmeter

When establishing an ESD Control Plan, if a conductor that comes into contact with an ESDS item cannot be grounded or equipotential bonded, then the process must ensure that the difference in potential between the conductor and the contact of the ESDS item is less than 35 volts. This can be accomplished by measuring the ESDS item and the conductor by using a non-contact electrostatic voltmeter or a high impedance contact electrostatic voltmeter. (Table 3)

Worksurfaces
Worksurfaces are defined as any surface on which an unprotected ESDS item is placed. Due to a wide variety of applications for worksurfaces, specific requirements that could be broadly applied are difficult to determine. If there is a concern for CDM failures, then a lower limit of 1.0 x 106 ohms for point to point and point to groundable point should be considered.

Packaging
The organization shall define ESD protective packaging requirements, both inside and outside the EPA per ANSI/ESD S541 or in accordance with the contract, purchase order, a drawing or other documentation necessary to meet customer requirements.

NOTE: ESDS items are placed on packaging materials and the ESDS items have work being performed on them; then the packaging materials become work surfaces. The work surface requirements for resistance to ground apply.

For additional information on periodic testing of Ionizers, see ANSI/ESD SP3.3.

Marking
ESDS items, system or packaging marking shall be in accordance with customer contracts, purchase orders, drawing or other documentation. When the contract, purchase order, drawing or other documentation does not define ESDS items, system or packaging marking, the Organization, in developing the ESD Control Program Plan, shall consider the need for marking. If it is determined that marking is required, it shall be documented as part of the ESD Control Program Plan.

Annex A (Informative) - Additional Process Considerations

(This annex is not part of ESD Association Standard ANSI/ESD S2020-2014)

The following sections provide guidance and outline documents that are available to help the users evaluate additional control products and equipment. Users will need to develop their own acceptance and compliance verification criteria as the industry has not yet defined required limits for these items.

Automated Handling Equipment
ANSI/ESD SPIO.I, Automated Handling Equipment (AHEI). 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.

Gloves
ANSI/ESD SP15.1 PDF, Standard Practice for In-Use Resistance Testing of Gloves and Finger Cots, 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 practice applies to all gloves and finger cots used to control ESD. This standard practice provides data that is relevant in the user's specific environment and application.

Conveyor Systems
Conveyor systems often have unprotected ESD sensitive items on them for movement of the 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.

Table 4. 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 Method 3015
MIL-STD-750 Method 1020
MIL-PRF-19500
MIL-PRF-38535
CDM ANSI/ESDA/JEDEC JS-002
JEDEC JESD22-C101
MM (For Information Only) ANSI/ESD STM5.2
JEDEC JESD22-A115
Annex C (Informative) - Related Documents

(This annex is not part of ESD Association Standard ANSI/ESD S2020-2014)

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 I U.S. Government

  1. MIL-STD-3010, "Federal Test Method Standard" (Free PDF)
  2. MIL-PRF-81705, "Barrier Materials, Flexible, Electrostatic Free, Heat Sealable" (Free PDF)
  3. MIL-E-17555, "Electronic and Electrical Equipment, Accessories, and Provisioned Items (Repair Parts): Packaging of" (Free PDF)
  4. MIL-STD-1686, "Electrostatic Discharge Control Program for Protection of Electrical and Electronic Parts, Assemblies and Equipment (Excluding Electrically Initiated Explosive Devices)" (Free PDF)
  5. MIL-HDBK-263, "Electrostatic Discharge Control Handbook for Protection of Electrical and Electronic Parts, Assemblies. and Equipment (Excluding Electrically-initiated Explosive Devices)" (Free PDF)
  6. MIL-M-38510, "General Specification for Military Microcircuits" (Free PDF)
  7. MIL-P-82646, "Plastic Film, Conductive, Heat Sealable, Flexible" (Free PDF)
  8. MIL-PRF-87893, "Workstations, Electrostatic Discharge (ESD) Control" (Free PDF)
  9. MIL-STD-129, "Marking for Shipment and Storage" (Free PDF)
  10. MIL-STD-1285. "Marking of Electrical and Electronic Parts" (Free PDF)
  11. MMA-1985-79. Revision 3, "Standard Test Method for Evaluating Triboelectric Charge Generation and Decay" (Free PDF)

Industry Standards

  1. ANSI/lEEE-STD-142 Free PDF, "IEEE Green Book (IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems)"
  2. JESD 625, "Requirements for Handling Electrostatic-Discharge-Sensitive (ESDS) Devices" (Free PDF)
  3. EIA-583, "Packaging Material Standards for Moisture Sensitive Items" (Free PDF)
  4. TR3.O-02-05, "Selection and Acceptance of Air Ionizers"
  5. ESDSIL, "Reliability Analysis Center (RAC) ESD Sensitive Items List"
  6. ELA-471, "Symbol and Label for Electrostatic Sensitive Devices"
  7. IEC 61340-5-1, "Protection of Electronic Devices from Electrostatic Phenomena - General Requirements"
  8. VZAP, "Electrostatic Discharge Susceptibility Data" (Free PDF)
  9. ISO 9001, "Quality management systems - Requirements"
Additional Documentation

All ANSI/ESD S20.20 Documents

Unless otherwise specified, the following documents of the latest issue, revision or amendment form a part of this standard to the extent specified herein:

  1. ESD ADV1.0, "ESD Association's Glossary of Terms"
  2. ANSI/ESD S1.1, "Wrist Straps"
  3. ANSI/ESD STM 2.1, "Garments"
  4. ANSI/ESD 3.1 Ionization
  5. ANSI/ESD SP3.3, "Periodic Verification of Air Ionizers"
  6. ANSI/ESD S4.1, "Worksurfaces - Resistance Measurements"
  7. ANSI/ESD STM4.2, "ESD Protective Worksurfaces - Charge Dissipation Characteristics"
  8. ANSI/ESD S6.1, "Grounding"
  9. ANSI/ESD STM7.1-2013, "Characterization of Materials"
  10. ANSI/ESD STM9.1, "Footwear - Resistive Characterization"
  11. ANSI/ESD SP9.2, "Footwear - Foot Grounders Resistive Characterization"
  12. ANSI/ESD STM12.1, "Seating - Resistive Measurement"
  13. ANSI/ESD S13.1, "Electrical Soldering/Desoldering Hand Tool Test Methods for Current Leak"
  14. ESD TR53, "Compliance Verification of ESD Protective Equipment and Materials"
  15. ANSI/ESD STM97.1, "Floor Materials and Footwear - Resistance Measurement in Combination with a Person"
  16. ANSI/ESD STM97.2, "Floor Materials and Footwear - Voltage Measurement in Combination with a Person"

Additional ESD Documentation

  1. Guide to All Things ESD
  2. Recommendations For Use and Testing of ESD Protective Garments in the Electronics Industry
  3. ANSI/ESD Handbook

How To Get ANSI/ESD S20.20 Certified

Compliance with this standard can be demonstrated through third-party certification. The certification process is similar to any quality management system certification such as ISO 9001. Information on the certification process can be obtained by contacting an ESD Association approved Certification Body.

Note: For a list of ESD Association approved Certification Bodies, see ESDA Certification Bodies.