1. 2016 EOS/ESD Manufacturing Symposium
China
Factory ESD Grounding System
Design Application
Copper Hou

2. 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

3. Background
• 3 types ESD ground systems are often discussed
– AC equipment ground based
– Separated from AC equipment ground
– Auxiliary ground
Slide 3

4. 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

5. 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.

6. Typical ESD Grounding Application
Slide 6
● All conductive and dissipative items in an EPA are grounded.

7. 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.

8. Typical Equipotential Bonding ESD
Protection in Field Service Application
Slide 8
IEC 61340-5-1
● Personnel and worksurface are bonded to the equipment.

9. 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

10. AC Equipment Ground as ESD Ground
• Preferred ESD ground system by ESDA and IEC.
Slide 10

11. 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

12. 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

13. Separate ESD Ground
• China SJT defines separate ESD earth ground system
– Earth resistance<10Ω for equipment level, <4Ω for component level
Slide 13

14. 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

15. EOS Due to Separate Grounding
• Electrical soldering rework/repair process.
Slide 15

16. 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)
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17. 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

18. Auxiliary Ground as ESD System Ground
• Auxiliary ESD grounding system application
Slide 18
NASA-HDBK8739.21

19. 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

20. 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

21. 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
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2

22. 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

23. 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
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2

24. 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.

25. 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

26. 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