Teseq ESD Simulator Verification

Transcription

1 Teseq ESD Simulator Verification

2 Background Greg Senko, President Teseq Inc. North American division of Teseq Laboratory Technical Manager Edison NJ This presentation was first given in 2003 when lab was Schaffner Co-authored with Ken Wyatt, Lab Manager Agilent Technologies Teseq first ISO accredited by A2LA March Audited for re-accreditation in 2008 and 2010 & Teseq scope of accreditation now includes IEC : as well as many other industry standards: EN , IEC 801-2, ISO TR 10605, ISO 10605, SAE J , ANSI C63.16, FORD ES-XW7T-1A278-AC, GMW 3097, DC-10614, DC Presentation includes these updates and experiences 2

3 Outline Virtually every EMC laboratory has one or more ESD simulator. Many are equipped to verify the ESD simulators performance but few to the latest requirements. Topics: Verification techniques, including ISO, SAE, ANSI and IEC standards Latest changes to verification requirements How the new systems compare to older systems Practical aspects of measurement setup and performance Conflicts between specifications Recommendation for air-discharge verification 3

4 ESD Simulator Verification What parameters must be measured? Tip voltage continuous, not discharge Current waveform contact discharge Peak Rise time Current at 30ns (for IEC network) Current at 60ns (for IEC network) Current waveform air discharge (automotive only) Rise time Time Constant 4

5 ESD Simulator Verification Measuring tip voltage Measured at standard test levels: ±2kV, ±4kV, ±6kV, ±8kV, ±15kV and ±25kV Measured using Electrometer or Giga-ohm meter Most standards don t specify requirements ISO specifies 100GOhm minimum input impedance The simulator s tip voltage not affected by the measurement If a Giga-ohm meter is used, the simulator must continuously charge the high-voltage capacitor 5

6 ESD Simulator Verification Tip voltage measurement using Giga-ohm meter 6

7 ESD Simulator Verification Idealized ESD simulator waveform 7

8 ESD Simulator Verification Actual waveform measurement 8

9 Measurement System How do we measure the current waveform? A low impedance shunt is used to represent a discharge into a large metallic object The shunt impedance is < 2.1 Ohms Block diagram: TARGET ESD ATTENUATOR OSCILLOSCOPE 9 GROUND PLANE CABLE

10 Measurement Target Axial resistors IEC target Found where older standard editions are referenced Difficult to precisely control dimensions, center can shift Poor impedance control 10

11 Insertion loss [db] Typical transfer characteristic of a Pellegrini target (MD 101) Ins ertion los s of the Pellegrini target 30 S21_dB MHz f_mess 6GHz frequency [Hz]

12 Measurement System Typical ESD current measurement system with Faraday cage example from IEC

13 Measurement System Typical ESD current measurement system actual system used in some Teseq labs 13

14 Attenuators Choosing attenuators Target transfer function is ~1V/A when loaded by 50 Ohms Contact mode peak current at 8kV is ~30A Input range of most oscilloscopes is < 10V in 50 Ohm mode Attenuator is needed to reduce the signal level 20dB is typically chosen for 10:1 ratio Contact mode to 25kV may require additional attenuation 14

15 Attenuators Choosing attenuators Low power attenuators may damaged by the short term peak power Attenuators are available with 1kW peak power ratings Use an 18GHz attenuator with low SWR, < 1.25 to 8GHz The attenuator accuracy requires that the entire chain be calibrated Accuracy variation db Percentage % % % % % 15

16 Cables Choosing cables A low loss cable is required Cable length < 1m is required by most standards Double shielding is required by most standards The ANSI standard recommends RG 400 RG 214 is twice the diameter, 1/2 the loss and is commonly available 16

17 Bandwidth Oscilloscopes - bandwidth The BW/risetime of the oscilloscope is the single most limiting factor to accurately measure the pulse risetime. The true risetime is related to the observed risetime as follows: risetime esd _ pulse risetime 2 observed risetime 2 measurement _ chain The above correction is proposed in the ANSI draft standard and assumes a Gaussian rolloff in frequency response. However most digitizers use a sharper cutoff filter, 20dB/decade or higher. 17

18 ESD Simulator Verification How does bandwidth affect observed risetime? Let s assume a Gaussian rolloff Oscilloscopes - bandwidth Pulse Risetime (ps) Scope BW (GHz) Scope Risetime (ps) Observed Risetime (ps) Difference % Error % % % % % % 18

19 ESD Simulator Verification Oscilloscopes sampling rate Single-shot sampling rate is the key Sharp/traingular peak requires fast sample rate Risetime of 800ps from 10%-90% is 80% of waveform 10Gs/s = 100ps/sample 8 samples in 800ps or 10%/sample! Since peak is symmetrical and somewhat rounded actual error is < 5% Effective sampling rate increased by capturing multiple shots Must have stable waveform Contact mode only - never for air discharge Shot to shot variation is low for most simulators Should be used for verification - not for calibration 19

20 ESD Simulator Verification Shot to shot variation 20 shots 33.3A peak Std dev.425 ±0.64% of peak 898ps Rise Std dev 11.9 ±0.66% of risetime 20

21 Sampling Rate Oscilloscopes sampling rate SAE and ISO recommend 4Gs/s minimum 2 Gs/s A -16.0% 10 Gs/s A -2.9% 5 Gs/s A -3.8% 20 Gs/s 33.18A 21

22 Interpolation / Vectors Oscilloscopes interpolation ON or OFF? Interpolation ON Interpolation OFF 22

23 ESD Simulator Verification Other factors Dos and don ts Shielding Do we need it? Position of ground cable Will it affect waveform? Orientation of simulator Will it affect waveform? Automatic Measurements Must use Min and Max values to calculate 10% and 90% points Other cables Keep them well separated 23

24 Faraday Cage? Oscilloscope shielding do we need it? Standards say yes, but probably not necessary - use distance test Scope inside chamber Scope at corner of plane Scope next to simulator 24

25 Measurement System Working ESD current measurement system without Faraday cage 25

26 Ground Cable Ground cable position Does affect results peak, rise and duration 20 Gs/s A, 891ps Natural loop Loop closer to plane 20 Gs/s A, 926ps 26

27 Simulator Orientation Simulator orientation to target Does affect results peak, rise and duration 20 Gs/s A, 891ps 20 Gs/s A, 913ps 20 Gs/s A, 945ps Simulator on axis Simulator up 10 Up 30 27

28 Air Discharge Waveform Air discharge What risetime/peak do you want? Approach speed and environmental factors will greatly affect results - not repeatable Obtaining a passing waveform is a matter of patience! 28

29 The New IEC -4-2 Changes to Simulator Verification in IEC : 2008 Method for measuring low frequency system transfer impedance Improved measurement target with RF specifications to 4GHz Target calibration adapter defined Minimum 2GHz oscilloscope bandwidth Faraday cage may not be required Peak current tolerance relaxed from ±10% to ±15% Minimum rise time reduced from 700ps to 600ps Ground cable position defined Uncertainty calculation examples in Appendix E 29

30 Target Evolution Target design history IEC 801-2: 1991 No longer referenced by any current standard No performance specifications Poor design - lots of ringing Small ground plane IEC : 1995, 2001 Referenced by virtually all current standards No performance specifications Transfer function zero at 5-6 GHz IEC : New design with flatness specified to 4GHz 2GHz Oscilloscope required Adapter to evaluate high frequency performance 30

31 A Better Target IEC : 2008 Target (example) SMD resistors Tighter tolerances Better impedance control 31

32 ESD Simulator Verification Waveforms of IEC target vs. ANSI target IEC target ANSI target Less HF ringing and shows true peak shape 32

33 Commercial Target System New target with adapter to measure transfer characteristics Calibration Adapter Measurement Target 33 Tool for removing center

34 Target Calibration Calibrating the target-attenuator-scope chain It is recommended that the DC transfer function of the entire chain be measured as follows: Inject a known current Measure the resulting voltage at the oscilloscope The attenuation factor = Injected current / Observed Voltage Attenuation factor is used to correct waveform amplitude CURRENT SOURCE TARGET CABLE ATTENUATOR ATTENUATOR OSCILLOSCOPE GROUND PLANE 34

35 Target Calibration IEC target and adapter specifications Variation of attenuation of the adapter-target-attenuator-cable chain < ±0.5dB from DC to 1GHz (< ±5.9%) < ±1.2dB from 1GHz to 4GHz (< ±14.8%) Adapters must be tested too! Return loss of two adapters face-to-face > 30dB from DC to 1GHz > 20dB from 1GHz to 4GHz Insertion loss of two adapters face-to-face < 0.3dB up to 4 GHz 35

36 Ground Cable Orientation IEC : 2008 and ISO 10605:

37 Scope Bandwidth Effects TDS 7104, 1GHz, 10GS/s Peak I 29.02A Rise 827ps I A I A Sample rate - 40ps/s Oscilloscope 1GHz vs. 2.5GHz oscilloscope 37 TDS 7254, 2.5GHz, 20GS/s Peak I 28.17A Rise 803ps I A I A Sample rate 10ps/s

38 ESD Simulator Verification Measurement uncertainty The estimated bounds of the deviation of a measured quantity from its true value List all the possible error sources and compute the uncertainty Uncertainty budget for each measured parameter Statement of confidence that can be placed in the value of uncertainty Does measured result truly fall within acceptable limits? National Association for Measurement and Sampling publication NIS81, The Treatment of Uncertainty in EMC Measurements Extensive reference information with examples in IEC : 2008 Appendix E 38

39 The New Changes to Simulator Verification in ISO 10605: 2008 New RC networks added to existing 150pF / 2kΩ, 330pF / 2kΩ 150pF/ 330Ω same specs as IEC pF/ 330Ω DC New networks have IEC-like limits ±10% peak vs. +30/-0% No air discharge verification variability too high Voltage Approach speed Humidity Arc length Ionization 39

40 Comparing Standards New 330/330 network No issues RC Network: 330pF, 330Ω Contact Rise Time IEC : 2001 IEC : 2008 ISO 10605: 2008 Ford CS-2009, GMW 3097: 2006 ISO 10605:2001 O O ns O O 1rst Peak O O +10/-10% O O Air Discharge O O O O O Current at 30, 60ns O O ±30% O O 40

41 Comparing Standards Certificate to IEC -4-2 does not fulfill ISO RC Network: 150pF, 330Ω Contact Rise Time IEC : 2001 IEC : 2008 ISO 10605: 2008 Ford CS-2009, GMW 3097: 2006 ISO 10605: ns ns ns O O 1rst Peak +10/-10% +15/-15% +10/-10% O O Air Discharge O O O O O Current at 30, 60ns ±30% ±30% ±30% O O 41

42 Comparing Standards 10605: 2008 Cert. does not fulfill Ford and GM, use 2001 ed. RC Network: 150pF, 2kΩ 330pF, 2kΩ Contact Rise Time IEC : 2001 IEC : 2008 ISO 10605: 2008 Ford CS-2009, GMW 3097: 2006 ISO 10605:2001 O O ns 1.0ns ns 1rst Peak O O +30/-0% +30/-0% +30/-0% Air Discharge O O O Current at 30, 60ns Rise 20ns, Time Const. Rise 5ns, Time Const. O O ±30% O O 42

43 That Pesky Air-Discharge! Requirements from ISO 10605: 2001 Only single events are allowed Start at least 15mm away from the target Approach slowly, 5mm/s or less Levels are 4, 8 and 15kV both polarities Rise time must be less than 5ns Acceptable waveforms must be repeatable at least 6 of 10 attempts Time constant is 300ns ± 60ns for 150pF network Time constant is 660ns ± 130ns for 150pF network Target from IEC : 1995 referenced, no target plane req s 43

44 That Pesky Air-Discharge! Series of 20 Discharges, 12 of 20 <5ns 4.63ns 6.66ns 7.79ns 3.02ns 8.10ns 4.16ns 4.35ns 5.89ns 2.82ns 3.35ns 3.03ns 5.39ns 3.25ns 5.56ns 3.10ns 5.45ns 4.12ns 3.63ns 2.70ns 5.14ns 44

45 That Pesky Air-Discharge! Series of 20 Discharges, Event #1 45

46 Do you Remember this Measurement Target? ISO 10605: 1994 Target from IEC with Ball Tip 46

47 Balls of Steel Spherical center exchanged for flat center 47

48 Spherical Center How do we know the HF characteristic is OK? Standard Center Rise 817ps Peak 27.9A Spherical Center Rise 822ps, +5ps, reproducibility 14ps Peak 28.0A, +0.1, reproducibility 0.24A 48

49 49 Spherical and Standard Center Waveforms Overlayed

50 That Pesky Air-Discharge! Summary Some checks should be applied There will be a high degree of variability shot-to-shot Internal contact discharge relays increase variability Environmental characteristics pay a big role Contact shape affects discharge waveform Flat targets perform worse than spherical centers Spherical center does not alter target characteristics 50

51 Multiples Are they really there? Very hard to capture A second and sometimes a third discharge occurs Typically >100ms between discharges Fast sampling rate required to catch event, >1Gs/s Long record length required For 500ms, 500Mb! Peak detect sampling mode works well 51

52 Multiples Two ESD simulators from different manufacturers Photos are enhanced to make peaks more visible 52

53 Multiples Why do they occur? At 15kV, the first discharge arc occurs well before the contacts touch Arc can be 5 to >10mm At 5mm/s, 1 2 seconds from first arc to contact The ESD discharge lasts for just 10 s of nanoseconds Arc extinguishes when current is low but before all energy discharged Additional discharge happens when tip gets close enough for new arc, approx ms after first event 53

54 ESD Simulator Verification Thank you for your attention Your feedback is welcome Gregory Senko, President Teseq, Inc