ESD Conseils DUBAN Michel 26000 VALENCE - FRANCE 1 ESD prevention People grounding by Flooring system and conductive shoes The institute of Physics…

ESD Conseils DUBAN Michel 26000 VALENCE - FRANCE

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ESD prevention

People grounding by

Flooring system and conductive shoes

The institute of Physics….. Electrostatic Measurement13 -th November 2001……


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The place of ESD at Workshop

• 1 - 60 to 70 % of electronic components failures are due to ElectroStatic Discharges (ESD).

• 2 – In 1991 HP said : 90 % of ESD failures are latent ones .

A latent failure does not give an immediate failure but entrain a failure later, a few days or some months later.

This kind of failure affect directly the reliability of electronic equipments.


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ESD Cost • Many data are available from several sources. • Hewlett Packard, at the end of 80 th, estimated the gain

equivalent to 50 000 PC the first year following the setting up of an ESD control program.

• Estimated cost given for year 1993 at world level: 8 % of electronics market (about FFR 45 milliards

(GBP ~ 5 billions).• My own experience (15 years with ESD protection): -

About 10 ESD faults formally identifiedCost from GBP 100 to GBP 100, 000

• One example: During qualification of new ASIC components 20 components failed, cost ~ GBP 15,000.

• But ESD failures, are difficult to identified !….


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Different ESD models (RD 1)

• 1 - Human body Model : HBM,

• 2 - Machine Model : MM,

• 3 - Charged Devices Model : CDM,

• 4 - Field Induce Model : FIM ,

• 5 - Charged Chip Model : CCM .

The ESD Model constraints depend on process used.

• A basic rule:

No charge, no discharge.


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Components class 0 thresholdsModel Class / Thresholds

HBM 0 < 250 V

MM M 0 < 25 V

CDM C 0 < 125 V

• In an Electro Static Discharge control plan, the sensitivity of components to be handled, must be well known.

• The rules and practices must take into account the sensitivity of components and the processes used.


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Handle Components/equipments class 0.• Handling of class 0 components or equipments involve using every

possible methods to fight against the presence of electrostatic charges:• Grounding the person‘s body, (wrist-strap, conductive shoes on

dissipative floor);• Personal equipment (smocks, wrist-strap and its controller, conductive

gloves,…• Grounding materials or equipments (working surface , iron…),• Shielding,• Packaging (antistatic, conductive),• Ionization,• People training,• Audit…..

STATIC ELECTRICITY MUST BE UNDER CONTROL



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How to eliminate Electrostatic Charges?• Conductors materials:

Connect them to ground in respect of security rules, a person is a conductor too, he must be connected to ground.

• Insulating materials:Eliminate all insulating materials which are not necessary in the environment of the working surface.

Get the other conductors, with antistat for instance and connect them to ground.

• Elimination of parasitic electrostatic fields.Use, ionization systems, dissipative garnements, gloves…



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Standardization Procedure

• The rules, method and limits to eliminate the ESD risk are given in standard documents:

IEC 61340 5 -1 (RD2), IEC 61340 -5-2 (RD3).

• 1 - Methods:Elimination of electrostatic charges on person :. Persons can be grounded by antistatic wrist-strap or by

dissipative flooring system with conductive shoes, it depends of people activity.



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Standardization Procedure

• 2 - Limits

Depend on components sensitivity,

Most sensitive components are classified in class 0 in each model, and sensitivity can be less than 20 V.

"For components with an ESD sensitivity less than hundred volts the ESD coordinator have to define complementary rules“like indicated in standard documents ( 61 340-5).



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The objective• The objective was to handle, very sensitive and expensive electronic

equipments by people in standing-up-position.• ESDS (ESD sensitive components) are announced as very sensitive.

The threshold ESD in human body model is announced at about 20 V.• Smocks are antistatic/dissipative. The other classic equipments and

rules are respected.• The use of antistatic wrist strap entrains large difficulties. • So we want to use the floor as primary way to eliminate static charges.• In this configuration, people walking with conductive shoes must not

develop a static charge > 10 V (10 V take into account a margin of 6 db(1/2) versus ESD sensitivity of components).



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The performance of a flooring system can be characterised by the following specifications

• Body voltage generation (BVG) as low as possible: < 10 V in our case,

• Resistance to ground (Rtg):Lowest value must take into account security of persons.Highest value must guarantee the eliminations of electrostatic charges

and a low charge accumulation.• Surface Resistivity (Rs):Same constraints as for resistance to ground (Rtg)• Decay time (Td).The value must be low enough to eliminate charge in time compatible

with the human activity.



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How does the static electricity is generated?

• The static electricity is mainly generated by tribo-electricity, due to the shuffle, rubbing, between sole shoe and flooring covering.

• If the resistance between sole shoe and ground cannot eliminate the charges, there is accumulation of charges at sole shoe level.

• Then by influence, charges present on sole shoe attract the opposite charge at the feet of person who is charged by influence.

• As body is a conductor, the equivalent charges are present at the level of his hands.

• The charges balance is got when charge generation is equal as charges elimination. The potential obtained is equal to BVG.

• The simplified equivalent electrical diagram is given next page.



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Equivalent electrical diagram

Ig Cp

Rtg BVG

• BVG = I (g). Rtg 1*


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BVG measurementsOnly few manufacturers give data about this parameter.

These measurements are done following STM ESD 97-2 specification (RD 9).They are done with conductive shoes Transversal resistance < 10 M ohm

Materials Specification (V) 1*

Measure (V) 2* Comments

A 15 ~ 0 *1 value available for HR > 25 % *2 measure done for HR ~ 50 %

B < 10 ~ 3 1*Value available for HR > 25 % *2 measure done for HR ~ 50 %

C < 100 V ~ 5 1*Value available for HR >? % *2 measure done for HR ~ 50 %

D < 400V ~ 160 1*Value available for HR >? % *2 measure done for HR ~ 40 %

E No specification ~ 6 *2 measure done for HR ~ 50 %

F No specification 30/to140 F :others manufacturers tested *2 measure done for HR ~ 50 %

G < 2000 V (answer to 61340-4-1)

~ 6 *1 Following IEC 1340 (insulative shoes) *2 measure done for HR ~ 50 %

H < 2000 V (answer to 61340-4-1)

~ 6 *1 Following IEC 1340 (insulative shoes) *2 measure done for HR ~ 50 %

• Materials A to F are resin, Materials G and H are PVC carbon loaded.• F line cover several resin materials tested.


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Rtg Measurements

Materials Specification (M ohm)1*

Measure (M ohm) 2*

Comments

A Consistent resistance measurement at 10 to 500

V < 6 *1 value available for HR > 25 %

*2 measure done for HR ~ 50 %

B 1/100 4 (Few points <330)

1*Value available for HR > 25 % *2 measure done for HR ~ 50 %

C <1 (61340-4-1) <35 (ESD STM97-1)

<0.15 (61340-4-1) <35 (ESD STM97-1)

(few points <330

1*Value available for HR >? % *2 measure done for HR ~ 50 %

D 0.01 to 1 0.1 ~ to 20 K 1*Value available for HR > 25 % *2 measure done for HR ~ 50 %

E ? 0,1 to160 *2 measure done for HR ~ 50 %

F 0.1 to10 1 to 1000 F :others manufacturers tested *2 measure done for HR ~ 50 %

G 10 33/300*1 *1 Following IEC 1340 *2 measure done for HR ~ 50 %

H 0.1 4 *1 Following IEC 1340 (insulative shoes) *2 measure done for HR ~ 50 %

• Materials A to F are resin, Materials G and H are PVC carbon loaded.• F line cover several resin materials tested.


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Rs MeasurementsOnly few manufacturers give informations about this parameter

Materials Specification (M ohm)1*

Measure (M ohm) 2*

Comments

A Consistent resistance measurement at 10 to

500 V

<1 *1 value available for HR > 25 % *2 measure done for HR ~ 50 %

B 1/100 4 (Few points ? 330)

1*Value available for HR > 25 % *2 measure done for HR ~ 50 %

C / <0.15 (61340-4-1) <35 (ESD STM97-1) (few points <1000)

1*Value available for HR >? % *2 measure done for HR ~ 50 %

D 0.01 to 1 0.1 ~ to 20 K 1*Value available for HR >? % *2 measure done for HR ~ 50 %

E *2 measure done for HR ~ 50 %

F 0.1 to 10 1 to1000 *2 measure done for HR ~ 50 % Depends on probes used and materials

G 10 600 *1 Following IEC 1340 *2 measure done for HR ~ 50 %

H 0.1 4 *1 Following IEC 1340 (insulative shoes) *2 measure done for HR ~ 50 %

• Materials A to F are resin; Materials G and H are PVC carbon loaded. Materials with very low resistance < 10 K ohm are not include in these results and are not always good on BVG parameter.


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Theories….• U= RI

• Q = CV = it

S = 15*10–6 (r1 - r2)

(Where, S is the surface charge density, r1 and r2 are permitivity of both

materials in contact see RD 20)

• Q = s*S (Where S is the surface in contact)

• V = Vo e t/RC

( t = 2.2 RC V = 0,1 Vo; t = 5 RC V = ~ 0 V)



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Remarks (1)• Measurement of resistances on some resin flooring system with

ASTM probes (Ø 63.5 mm, weight 5 pounds) give very large variations.

• On same flooring system the use of IEC 61340-4-1 or 1081 probes give lower resistance values and better repeativity.

• But In case of difficulty with ASTM probes, very often BVG is larger than the lower resistance measured that we hope.

• Measurement on a good flooring system usually give very uniform resistance value, even with ASTM probes.

• Resistance values less than 100 M ohm is low enough. • So the best solution is to use the real configuration following the

documents ESD-STM 97-1-1999 with conductive shoes*(RD 8).

*Not all ESD shoes give the same results but these with Rt < 10 7 ohm usually give good results.


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Remarks (2)

• Measurements of Body Voltage Generation is defined by different standard documents (NF EN 1815, NF P 62-001, ESD ASTM 97-2 1999 ).

We choose American norm ESD ASTM 97-2 1999 this document advocate real configuration ( conductive shoes, low displacement).

• For decay time measurements, normalisation document advocate to measure from 1000 V to 100 V; but an American flooring system manufacturer measure this parameter from 100 V to 10 V(it depends of needs).


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Apparatus (1)• Resistance measurements• Megohmeter

Measure voltage 10 /100 VResistance measure : 10 4 < R (ohm) ≧ 10 12.Normalised probes :ASTM (difficult to use on hard resin flooring system) ,IEC 61340-4-1, NF EN 1081.

*Repeteative measures at 100 or 10 Volts are a good omen to obtain à low BVG.

• Conductive Shoes Transversal resistance < 10 M ohm



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Apparatus (2)• Voltage measurements• Charge analyser:

Voltage > or = 1100 VAdjustable thresholds.

time measurements From 0.1 to ~ 60 seconds.• Graphic recorder:• Thermometer/ Hygrometer .

Many similar materials can be used.



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Conclusions• The single characterisation of flooring system by measurement of resistance

to ground is not sufficient. The performance of a flooring system must be characterised by the following specifications with RH compatible with the environment.

• Body voltage generation (BVG) (following ESD-STM 97-2-1999) : < 10 V (For ESDS 20 V)

• Resistance to ground (Rtg) : • Rtg1* (following IEC 61340-4-1 / NF EN 10 85)

10 5 < Rtg 1 (ohm) < 10 8 • Rtg2 (following ESD-STM 97-1-1999)

10 5 < Rtg 2 (ohm) < 10 8 • Surface Resistivity (Rs*):

10 5 < Rs (ohm) < 10 8

• Decay time (Td)Td < 0.3 s (1000 V to 100 V or less)


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Final Conclusion • The European standardization, the flooring

system manufacturers, and the users should take into account these methods and

parameters.


Do not forget :A static dissipative flooring system with conductive shoes is an element

of an ESD protection system. in workshop. It allow to completely eliminate ESD risk Human Body Model in standing working position.


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Reference Documents (1)• RD 1: HDBK 263 Electrostatic Discharge Control Handbook for Protection of Electrical

and Electronic Parts, Assemblies and Equipments.• RD 2: ICE 61340 -5-1 Protection of Electronic Devices from Electrostatic phenomena-

general requirements.• RD 3: ICE 61340 -5-21 Protection of Electronic Devices from Electrostatic phenomena-

user guide.• RD 4: ICE 61340 -4-1 Electrostatic behaviour of floor covering and installed floors.• RD 5: NF EN 1081 Revêtement de sol Résilient ; détermination de la résistance électrique. • RD 6: NF EN 1815 Revêtement de sol Résilient et Textiles; Evaluation de l’accumulation

des charges électrostatiques.• RD 7: NF 61 002 Revêtement de sol, propriétés antistatiques.• RD 8: ESD STM 97-1 Floor Materials an Footwear- Resistance Measurement in

combination with a Person.• RD 9: ESD STM 97-2 Floor Materials an Footwear Voltage Measurement in combination

with a Person.• RD 10: ANSI ESD 20.20 Protection of an Electrical and Electronic Parts, assemblies and

Equipment


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Reference Documents (2)• RD 11: ANSI /ESD S 03.1 Ionization• RD 12: EOS /ESD Standard S 5, Human Body Model (HBM) ESD Sensitivity

Testing• RD 13: EOS /ESD DS 03/01/1996 • RD 14: Warmbier internet site address • RD 15: ESD Systems Internet site address • RD 16: ESD Association Internet web site address (www.esda.org)• RD 17: NASA Internet site address • RD 18: Grounding Personal via the Floor/ Footwear System Siemens AG document

presented at the EOS/ESD symposium, Santa Clara USA 1997.• RD 19: Electrostatic Damage in.Electronics Devices and Systems (William D.

Greason)• RD 20: Electrostatic discharge (Michel Mardigian) Some other internet sites from manufacturers of resin or PVC flooring system, can

be consulted.


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Knowledge

• Mister P PILLET the person who asked me to work on ESD risk about fifteen years ago. M. B. DEUTZ D'ARRAGON the person who asked for me to work again on this problem, and M P.MARSAL and M H. ZUGAJ for their listening during these last months, all these people belong to Alcatel Space Industries company.

• Warmbier, a German company for his presentation of the difficulties with resin flooring in 1999 and the solution proposed; I specially want to thank M. Meir GOLAN and M. PFEIFLE and their French representative M A.CHAPON.

• ESD Systems for its Internet site and the interesting answers from M. A.RYNE

• The persons of different flooring systems company who help me and send me samples to do my work.

• And my correctors madam M. BESSON and J.C. LEFRANC.