Factory ESD Grounding System Design Applications

2016 EOS/ESD Manufacturing Symposium

China

Factory ESD Grounding System

Design Application

Copper Hou

Objectives

● This paper would discuss the followings:

– To demonstrate how grounding protect objects

from being damaged by ESD

– To analyze the effectiveness of different ESD

grounding schemes

– To propose a reliable ESD grounding approach to

achieve both personnel safety and ESD

protections to sensitive items.

Slide 2

Background

• 3 types ESD ground systems are often discussed

– AC equipment ground based

– Separated from AC equipment ground

– Auxiliary ground

Slide 3

Safety Concern of AC Leakage from AC Equipment

(problem with AC equipment based grounding)

• Grounding risks related with AC equipment

– Electrical shock hazard against ground with AC leakage

Slide 4

How Grounding Avoids ESD Happening?

● Grounding Principle

– Potential differences is the cause to make charge transferring.

– Grounding equals all the objects (conductive, dissipative) at the same

potential with the earth (virtually zero) by the electrical connection.

– There would be no charge transferring between grounded objects

(conductive, dissipative), therefore no ESD events could occur.

Slide 5● Note: grounding is ineffective to insulators.

Typical ESD Grounding Application

Slide 6● All conductive and dissipative items in an EPA are grounded.

How Grounding Protect ESD?

● Equipotential bonding Principle

– Bonding equals the objects at the same potential, usually not near the

earth potential.

– No potential differences, no charge transferring (no ESD).

Slide 7

● No potential difference, makes No ESD occurrence!

Equal potential maintained between V1 and V2.

Typical Equipotential Bonding ESD

Protection in Field Service Application

Slide 8

IEC 61340-5-1

● Personnel and worksurface are bonded to the equipment.

Ref. industrial grounding standards

• ESDA ANSI/ESD S20.20

– ANSI/ESD S6.1, NFPA 70 (Article 250 part Ⅲ, grounding

electrode system)

• IEC 61340-5-1

– IEC 61340-5-1, Country/region National Electrical Codes

• China, SJT: separate ESD earth ground

– SJ/T 10533 for equipment level

– SJ/T 10630 for component level

Slide 9

AC Equipment Ground as ESD Ground

• Preferred ESD ground system by ESDA and IEC.

Slide 10

Why Prefer AC Equipment Ground?

• AC equipment ground as ESD system ground

– Better equipotential between AC equipment and ESD control items

within an EPA

– Wide applicability for facilities to set up ESD system ground

Slide 11

Why Prefer AC Equipment Ground?

• If AC equipment ground is unavailable within an EPA

– Extend the ESD ground from the EPA with AC ground

– Or take equipotential bonding option instead

Slide 12

Separate ESD Ground

• China SJT defines separate ESD earth ground system

– Earth resistance<10Ω for equipment level, <4Ω for component level

Slide 13

Risks of Separating ESD and AC Grounds

• Higher electrical potential differences.

• Equipotential ESD protection between AC

equipment and ESD items would be weakened.

Slide 14

EOS Due to Separate Grounding

• Electrical soldering rework/repair process.

Slide 15

Solution to Separate Grounding

• Add electrical bonding between AC equipment ground and

ESD ground: minimize the potential difference

– Bonding resistance<25Ω (recommended by ESDA & IEC)

Slide 16

Auxiliary Ground as ESD System Ground

• Secondary ESD system ground by ESDA and IEC

– Added <25Ω bonding to lower the potential difference

– Still not the best equipotential approach to ESD protection

Slide 17

Auxiliary Ground as ESD System Ground

• Auxiliary ESD grounding system application

Slide 18

NASA-HDBK8739.21

Hybrid Equipotential Grounding Scheme

• Hybrid equipotential grounding features

– Dual earth grounding systems makes double reliability, AC equipment

grounding and ESD grounding (more relied)

– Best equipotential protection within an EPA through CPG bonding

Slide 19

Personnel Electrical Shock Safety

• Ground fault circuit interrupters (GFCI) protection

– National/local electrical codes/legislation

– Triggering leakage current-6mA (UL943)

– ESDA & IEC recommendation

Slide 20

Personnel Electrical Shock Safety

• Even if GFCI out of function

– Most AC leakage would flow to earth through equipment ground

– Current limiting design of personnel grounding items provide the

additional protections.

Slide 21

1

2

Personnel Electrical Shock Safety

• Personnel electrical safety concern in ESD controls

– Current limiting shall be considered in exposure of

hazardous AC electrical sources

– 0.7 mA peak current limit defined by UL 1950.

Slide 22

Current limiting shall be considered

Personnel Safety in Hybrid Grounding

• If AC leakage occurs

– Double grounding systems to protect against AC leakage

– Equipotential bonding benefit both ESD & Safety

Slide 23

1

2

Electrical Shock Case

• Electrical shock resolved by hybrid grounding

– Eliminated by adding separate ESD grounding to the AC equipment.

Slide 24

Cause: Equipment ground wire worn

(of the power cord) induce ~110V AC

voltage on the machine chassis.

Solution: add ESD grounding

onto equipment chassis.

Conclusions

• AC equipment ground is preferred as ESD Ground

– Well equipotential ESD protection

– Wide availability for facility applications

• Separate ESD grounding has higher potential risks

– Higher potential difference from AC equipment

• Personnel safety should be assured

− GFCI application involved with AC equipment

− Current limiting design of personnel grounding items

• Hybrid equipotential grounding scheme provides

– Double grounding reliability & best equipotential for ESD controls.

Slide 25

Acknowledgements

• Appreciate Edward H. Russell to share his analysis

of safe ESD grounding design.

• ESDA ANSI/ESDS20.20, ANSI/ESDS6.1 and IEC

61340-5-1 are important reference to this paper,

appreciate their technical sharing;

• I also show the sincere thanks to Rita who extended

the great supports to help me make the paper better

tailored to this symposium.

Slide 26