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Grounding Considerations for an Electrostatic-Protected Area

TUTOR: SL HO

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Fundamental principles

Fundamental principles in electrostatic-protected area (EPA) :

• Electrically interconnecting all conductive and dissipative items—that is, bonding them;

• and attaching them to ground;

• an area free of differences in electrical potential - EPA

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Choosing the Grounding System

Choosing the Grounding System

• AC Equipment Ground

• Auxiliary Ground

• Equipotential Bonding

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AC Equipment Ground

Within EPA, the preferred ground is the AC equipment ground

• the third-wire terminal

• electrically bonds the AC equipment ground to the ground bus at the main service equipment panel of the facility

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Auxiliary Ground

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For some purposes only:

- to keep away any ESD spikes or electromagnetic-interference signals from electrical equipment that is not attached to that system in an EPA

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Auxiliary Ground

• RISK: the difference in potential that could exist between different grounding systems (AC grounding and the Auxiliary grounding)

• SO: auxiliary ground and ac equipment ground need to be bonded together whenever possible

• IF both grounding systems are present, resistance between AC and Auxiliary ground shall be < 25 ohms.

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Equipotential Bonding

appropriate for remote or field operations where equipment is being serviced and a properly set up EPA is not available

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- Electrically interconnecting All things in the area

- everything within the system will be at some shared potential (potential vs Ground may be elevated).

- “No difference in potential within the handling system, no discharge is possible”

- ESD-susceptible items within the system can be safely handled

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Next step in setting up the EPAEstablishment of a common-point ground

• The common-point ground device : can be anything, terminal strips, bus bars, copper cables, etc.

• All of the ESD technical elements—wrist straps, table mats, floor mats, and so on—are terminated, by means of their grounding wires, to the common-point ground.

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Common-point ground

• Common point ground – point to point < than 1ohm

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Important notes:

• Metal bench tops (stainless steel worksurfaces) MUST be connected directly to AC equipment ground with no added resistance. – Avoidance of CDM issue.

• Wires used within the EPA shall be of sufficient strength, not to be inadvertently broken or disconnected.

• Resistance of the conductor from the groundable point ground of any ESD technical element (worksurface, floor, chair, wrist strap…) to common point ground shall not be greater than 1 ohm.

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Important notes:

• Resistance of conductor from common point ground to the AC equipment ground shall not be greater than 1 ohm

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Measurement of the resistance of the ac equipment

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Compliance Verification of ESD ProtectiveEquipment and Materials ESD (TR53-01-06)

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Worksurfaces

Test Equipment

• An integrated checker or meter, whether it is a single meter or a collection of instruments that are capable of measuring at least 1.0 x 1010 ohms with a test voltage of 10 and 100 volts

(± 10%) DC open circuit.

• One electrode

• Two test leads of sufficient length

• DC Ohmmeter

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Wrist Straps

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Test Equipment• Integrated checker or meter, whether it is a single meter or a collection of instruments thatare capable of measuring from 5.0 x 104 ohms to at least 1.0 x 1010 ohms with a test voltagebetween 7 and 30 volts DC open circuit. Some integrated checkers require manual selectionto wrist strap resistance test ranges.• Hand-held electrode• One test lead of sufficient length

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Footwear

Test Equipment

• Integrated checker or meter, whether it is a single meter or a collection of instruments that

are capable of measuring from 5.0 x 104 ohms to at least 1.0 x 1010 ohms with a test voltage

between 7 and 30 volts DC open circuit. Some integrated checkers require manual selection

to Footwear resistance test ranges.

• Hand-held electrode

• Foot electrode

• Two test leads of sufficient length

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Flooring

Test Equipment

• Integrated checker or meter, whether it is a single meter or a collection of instruments that

are capable of measuring at least 1.0 x 1010 ohms with a test voltage of 10 and 100 volts

(± 10%) DC open circuit.

• One electrode

• Two test leads of sufficient length

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Garments (sleeve-to-sleeve test)

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Test Equipment• Integrated checker or meter, whether it is a single meter or a collection of instruments thatare capable of measuring at least 1.0 x 1012 ohms with a test voltage of 100 volts(± 10%) DC open circuit.• Two electrodes• Two test leads of sufficient length• Insulative support surface

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Seating

Test Equipment:

• An integrated checker or meter, whether it is a single meter or a collection of instruments that

are capable of measuring at least 1.0 x 1010 ohms with a test voltage of 10 and 100 volts

(± 10%) DC open circuit.

• One electrode

• Two test leads of sufficient length

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Mobile Equipment (Carts)

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Test Equipment• Integrated checker or meter, whether it is a single meter or a collection of instruments thatare capable of measuring at least 1.0 x 1010 ohms with a test voltage of 10 and 100 volts(± 10%) DC open circuit.• Electrode• Two test leads of sufficient length

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ESD test equipment

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Field Meter Detects ESD Potential from any SourceMeasure ionizer performance

ESD Wrist And Esd Heel Strap Tester

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ESD test equipment

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Wrist Strap/ Foot Wear Combo Tester

Surface Resistance Meter:Measures point-to-point resistance (RTT) & point-to-ground resistance (RTG).

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ESD test equipment

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Charged Plate Monitors are for testing ionizer performance

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Compliance Verification Plan

• establish “Compliance Verification Plan”

• measurement limits and the frequency

• shall document the test methods and equipment used for process monitoring and measurements

• Compliance verification records shall be established and maintained

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Compliance Verification Plan

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Technical

Control Item Limits Test Procedure Test Frequency Checked By

Wrist strap

(system test)

Rs < 1.0x107 Ω ESD Association

publication TR53:

Wrist strap section

Daily (before use) Operator

Footwear Rs < 1.0x107 Ω

Ohms

ESD Association

publication TR53:

Footwear Section

Daily (before use) Operator

Flooring Rg <1.0x106 Ω ESD Association

publication TR53:

Flooring Section

Once every 3

months

Site Facilities

maintenance

Work surface Rg < 1x109 Ω ESD Association

publication TR53

Once every 3

months

ESD

Coordinator

Wrist strap

connection

point

Rg < 1 Ω Annex A.1 of this

procedure

Once every 3

months

Quality

Department

Static

Generators

< 2,000 Volts/inch Annex A.2 of this

procedure

Once every 3

months

Quality

Department

Shielding bags Visual indications

of damage

Random visual

inspection

Once every 3

months

Quality

Department

Rs refers to system resistance including person, the wrist band and the grounding cord or ESD

footwear Rg refers to resistance to ground

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