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

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Presentation on theme: "ESD Conseils DUBAN Michel 26000 VALENCE - FRANCE 1 ESD prevention People grounding by Flooring system and conductive shoes The institute of Physics….."— Presentation transcript:

1 ESD Conseils DUBAN Michel VALENCE - FRANCE 1 ESD prevention People grounding by Flooring system and conductive shoes The institute of Physics….. Electrostatic Measurement 13 -th November 2001……

2 ESD Conseils DUBAN Michel VALENCE - FRANCE 2 The place of ESD at Workshop 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.

3 ESD Conseils DUBAN Michel VALENCE - FRANCE 3 ESD Cost Many data are available from several sources. Hewlett Packard, at the end of 80 th, estimated the gain equivalent to 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 identified Cost 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 !….

4 ESD Conseils DUBAN Michel VALENCE - FRANCE 4 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.

5 ESD Conseils DUBAN Michel VALENCE - FRANCE 5 Components class 0 thresholds 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.

6 ESD Conseils DUBAN Michel VALENCE - FRANCE 6 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 persons 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 No charge, no discharge.

7 ESD Conseils DUBAN Michel VALENCE - FRANCE 7 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… No charge, no discharge.

8 ESD Conseils DUBAN Michel VALENCE - FRANCE 8 Standardization Procedure The rules, method and limits to eliminate the ESD risk are given in standard documents: IEC (RD2), IEC (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. No charge, no discharge.

9 ESD Conseils DUBAN Michel VALENCE - FRANCE 9 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 ruleslike indicated in standard documents ( ). No charge, no discharge.

10 ESD Conseils DUBAN Michel VALENCE - FRANCE 10 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). No charge, no discharge.

11 ESD Conseils DUBAN Michel VALENCE - FRANCE 11 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. No charge, no discharge.

12 ESD Conseils DUBAN Michel VALENCE - FRANCE 12 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. No charge, no discharge.

13 ESD Conseils DUBAN Michel VALENCE - FRANCE 13 Equivalent electrical diagram BVG = I (g). Rtg 1*

14 ESD Conseils DUBAN Michel VALENCE - FRANCE 14 BVG measurements Only 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 A to F are resin, Materials G and H are PVC carbon loaded. F line cover several resin materials tested.

15 ESD Conseils DUBAN Michel VALENCE - FRANCE 15 Rtg Measurements Materials A to F are resin, Materials G and H are PVC carbon loaded. F line cover several resin materials tested.

16 ESD Conseils DUBAN Michel VALENCE - FRANCE 16 Rs Measurements Only few manufacturers give informations about this parameter 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.

17 ESD Conseils DUBAN Michel VALENCE - FRANCE 17 Theories…. U= RI Q = CV = it S = 15*10 –6 ( r 1 - r 2 ) (Where, S is the surface charge density, r 1 and r 2 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) No charge, no discharge.

18 ESD Conseils DUBAN Michel VALENCE - FRANCE 18 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 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 with conductive shoes*(RD 8). *Not all ESD shoes give the same results but these with Rt < 10 7 ohm usually give good results.

19 ESD Conseils DUBAN Michel VALENCE - FRANCE 19 Remarks (2) Measurements of Body Voltage Generation is defined by different standard documents (NF EN 1815, NF P , ESD ASTM ). We choose American norm ESD ASTM 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).

20 ESD Conseils DUBAN Michel VALENCE - FRANCE 20 Apparatus (1) Resistance measurements Megohmeter Measure voltage 10 /100 V Resistance measure : 10 4 < R (ohm) Normalised probes : ASTM (difficult to use on hard resin flooring system), IEC , NF EN *Repeteative measures at 100 or 10 Volts are a good omen to obtain à low BVG. Conductive Shoes Transversal resistance < 10 M ohm No charge, no discharge.

21 ESD Conseils DUBAN Michel VALENCE - FRANCE 21 Apparatus (2) Voltage measurements Charge analyser: Voltage > or = 1100 V Adjustable thresholds. time measurements From 0.1 to ~ 60 seconds. Graphic recorder: Thermometer/ Hygrometer. Many similar materials can be used. No charge, no discharge.

22 ESD Conseils DUBAN Michel VALENCE - FRANCE 22 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 ) : < 10 V (For ESDS 20 V) Resistance to ground (Rtg) : Rtg1* (following IEC / NF EN 10 85) 10 5 < Rtg 1 (ohm) < 10 8 Rtg2 (following ESD-STM ) 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)

23 ESD Conseils DUBAN Michel VALENCE - FRANCE 23 Final Conclusion The European standardization, the flooring system manufacturers, and the users should take into account these methods and parameters. No charge, no discharge. 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.

24 ESD Conseils DUBAN Michel VALENCE - FRANCE 24 Reference Documents (1) RD 1: HDBK 263 Electrostatic Discharge Control Handbook for Protection of Electrical and Electronic Parts, Assemblies and Equipments. RD 2: ICE Protection of Electronic Devices from Electrostatic phenomena- general requirements. RD 3: ICE Protection of Electronic Devices from Electrostatic phenomena- user guide. RD 4: ICE 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 laccumulation des charges électrostatiques. RD 7: NF 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 Protection of an Electrical and Electronic Parts, assemblies and Equipment

25 ESD Conseils DUBAN Michel VALENCE - FRANCE 25 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 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.

26 ESD Conseils DUBAN Michel VALENCE - FRANCE 26 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.


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