慈溪市白云小學(xué)教職工考核表 TITLE

1、 ESD preventionPeople grounding by Flooring system and conductive shoesThe institute of Physics. Electrostatic Measurement13 -th November 2001 1The 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 fail

2、ures 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.2ESD Cost Many data are available from several sources.Hewlett Packard, at the end of 8

3、0 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 fa

4、ults 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 !.3Different ESD models (RD 1)1 - Human body Model : HBM,2 - Machine Model : MM,3 - Charged Devices M

5、odel :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.4Components class 0 thresholdsIn an Electro Static Discharge control plan, the sensitivity of components to be handled, must be well known. The rule

6、s and practices must take into account the sensitivity of components and the processes used.5Handle 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, (wri

7、st-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 UN

8、DER CONTROLNo charge, no discharge. 6How 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 env

9、ironment 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, glovesNo charge, no discharge. 7Standardization ProcedureThe rules, method and limits to elim

10、inate 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.No cha

11、rge, no discharge. 8Standardization Procedure2 - 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 complem

12、entary rules“l(fā)ike indicated in standard documents ( 61 340-5).No charge, no discharge. 9The objectiveThe 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

13、 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 walk

14、ing 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.10The performance of a flooring system can be characterised by the following specificationsBody voltage generation (BVG) as low

15、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

16、(Td).The value must be low enough to eliminate charge in time compatible with the human activity.No charge, no discharge.11How 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 coverin

17、g.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 cha

18、rges 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.12Equivalent electrical diagramBVG = I (g). Rt

19、g 1* 13BVG 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 ohmMaterials A to F are resin, Materials G and H are PVC carbon loaded.F line cover sev

20、eral resin materials tested. 14Rtg MeasurementsMaterials A to F are resin, Materials G and H are PVC carbon loaded.F line cover several resin materials tested.15Rs MeasurementsOnly few manufacturers give informations about this parameterMaterials A to F are resin; Materials G and H are PVC carbon lo

21、aded. Materials with very low resistance 10 K ohm are not include in these results and are not always good on BVG parameter.16Theories.U= RIQ = CV = itS = 15*106 (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 th

22、e 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.17Remarks (1)Measurement of resistances on some resin flooring system with ASTM probes ( 63.5 mm, weight 5 pounds) give very large variations.On same flooring system the use of IEC 61340-4-1 or 1081

23、 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 l

24、ess 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.18Remarks (2)Measurements of Body Voltage Genera

25、tion 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

26、V to 100 V; but an American flooring system manufacturer measure this parameter from 100 V to 10 V(it depends of needs). 19Apparatus (1)Resistance measurementsMegohmeter Measure voltage 10 /100 VResistance measure : 10 4 R (ohm) 10 12.Normalised probes :ASTM (difficult to use on hard resin flooring

27、system) ,IEC 61340-4-1, NF EN 1081. *Repeteative measures at 100 or 10 Volts are a good omen to obtain low BVG.Conductive Shoes Transversal resistance or = 1100 VAdjustable thresholds.time measurements From 0.1 to 60 seconds.Graphic recorder:Thermometer/ Hygrometer . Many similar materials can be us

28、ed.No charge, no discharge.21ConclusionsThe 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

29、(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 8Rtg2 (following ESD-STM 97-1-1999)10 5 Rtg 2 (ohm) 10 8Surface Resistivity (Rs*):10 5 Rs (ohm) 10 8Decay time (Td)Td 0.3 s (1000 V to 100 V or less

30、)22Final 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 wor

31、kshop. It allow to completely eliminate ESD risk Human Body Model in standing working position.23Reference 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 D

32、evices 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 Revtement de sol Rsilient ; dtermination de l

33、a rsistance lectrique. RD 6: NF EN 1815 Revtement de sol Rsilient et Textiles; Evaluation de laccumulation des charges lectrostatiques.RD 7: NF 61 002 Revtement de sol, proprits antistatiques.RD 8: ESD STM 97-1 Floor Materials an Footwear- Resistance Measurement in combination with a Person.RD 9: ES

34、D 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 Equipment24Reference Documents (2)RD 11: ANSI /ESD S 03.1 IonizationRD 12: EOS /ESD Standard S 5, Human Body Model (HBM) ESD Sensitivity TestingRD 13: EOS /ESD DS 03/01/1996RD 14: Warmbier internet site address RD 15: ESD Systems Internet site addressRD 16: ESD Association Internet web site address( )RD 17: NAS