Interconnect Impedance Measurements, Signal Integrity Modeling, Model Validation, and Failure Analysis. IConnect TDR Software.

Transcription

1 Rev. 8/27/21 Interconnect Impedance Measurements, Signal Integrity Modeling, Model Validation, and Failure Analysis IConnect TDR Software TDA Systems, Inc. Outline TDR Impedance Measurements in IConnect Interconnect Signal Integrity Modeling and Model Validation in IConnect Interconnect Failure Analysis in IConnect 1

2 Collateral Presentation Handouts Application materials TDR FAQ TDR References Signal Integrity Interconnect Significance Signal Integrity (SI): Digital Becomes Analog At high frequencies crosstalk and signal reflections can be perceived as logic triggers, and can be responsible for erroneous signal patterns EE Times, April 17, 1998, Special Section on Interconnects 2

3 Signal Integrity Interconnect Significance Interconnects at High Speeds Interconnects become transmission lines Interconnect discontinuities become lumped L-C networks Package Board Board Package Signal Integrity Interconnect Significance Signal Integrity Issues Propagation delay Reflections Crosstalk Loss Ground bounce Dispersion! SPICE/IBIS simulations and accurate interconnect models are required 3

4 Signal Integrity Interconnect Significance Consequences of Poor Signal Integrity Jitter and eye diagram degradation Result of losses and crosstalk Model with lossy and coupled line models Signal distortion, digital switching errors Result from crosstalk, reflections and ringing Crosstalk -> need coupled line modeling Reflections -> need impedance measurement accuracy and transmission line modeling Ringing -> need lumped element and transmission line modeling Signal Integrity Interconnect Significance Benefits of Addressing the Signal Integrity Early Avoid recalls and design failures $ Get product to market in time $ Avoid delays in time-critical design phases Lower design costs $ No redesigns results in savings! Achieve higher-performance system $ Gain market share with a better product 4

5 Signal Integrity Interconnect Significance Critical Interconnect Components PCB traces Single-run Differential On different layers PCB Vias Connectors and cable-connector assemblies Packages and multichip modules Sockets Failure Analysis Interconnect Significance Failure Analysis Issues Broken trace / bondwire (open) Lead to ground short Partial short or open Lead to lead short Plane to plane short 5

6 When is Interconnect Lumped? t prop delay t rise Practical rule of short or lumped (RLC) interconnect t rise > t prop delay 6 What are you trying to learn today? TDR Measurement s Measurement Basics Impedance Measurements Interconnect Probing and Fixturing Interconnect SI Modeling IConnect Modeling Methodology L and C Computation Transmission Line Modeling Coupled and Differential Line Modeling Lossy Line Modeling Interconnect FA " " " Open fault location Short fault location 6

7 Outline TDR Impedance Measurements in IConnect Basics True Impedance Profile Probing and Fixturing Interconnect Signal Integrity Modeling and Model Validation in IConnect Interconnect Failure Analysis in IConnect TDR Measurements Basics TDR Measurement Setup Cables TDR probe with signal and ground connections TDR Instrument 7

8 TDR Measurements Basics TDR Block Diagram V R source TDR Oscilloscope Front Panel V incident Cable: Z, td R source = 5 Ω Z = 5 Ω then V incident = ½V V reflected DUT: Z DUT Z termination TDR Measurements Basics TDR Visual Representation V Open circuit V Z load / (Z load + Z ) Z load > Z ½ V Matched load ½ V Short circuit Z load < Z 8

9 TDR Measurements Basics Practical Session Time base setup Vertical scale setup TDR setup Averaging and filtering Basic instrument calibration and operating conditions Normalization TDR Measurements Basics TDR Basic Equations ρ = V V reflected incident = Z Z load load Z + Z 2 t d V measured = V incident +V reflected V reflected = V incident Z Z DUT DUT Z + Z V incident Z DUT 1+ ρ V = Z = Z 1 ρ V incident incident + V V reflected reflected = Z 2 V V incident measured V measured 9

10 TDR Measurements Basics Inductance and Capacitance Analysis Shunt C discontinuity ½ V Z Z ½ V Series L discontinuity Z Z ½ V L-C discontinuity Z Z ½ V C-L-C discontinuity Z Z TDR Measurements Basics TDR Rise Time and Resolution Accepted rule of thumb for resolving two discontinuities t To resolve a 1 and a 2 as separate separate discontinuities: a 1 a 2 t separate > t TDR_risetime /2 More real case: resolving a single discontinuity a 1 t single a1 is not resolved if t single << t TDR_risetime Going beyond the TDR resolution and risetime: relative techniques Signal integrity modeling JEDEC standard Failure analysis golden device comparisons 1

11 TDR Measurements Basics Differential TDR Virtual ground plane Even and odd mode measurements R source Cable: Z, td V V TDR Oscilloscope Front Panel Virtual ground V incident V reflected DUT: Z DUT Cable: Z, td R source TDR Measurements Basics Practical Session Time base setup Vertical scale setup TDR setup Averaging and filtering Basic instrument calibration and operating conditions 11

12 Outline TDR Impedance Measurements in IConnect Impedance Measurements and IConnect TDR Software True Impedance Profile Appnote: PCB Interconnect Characterization from TDR Measurements Probing and Fixturing Interconnect Signal Integrity Modeling and Model Validation in IConnect Interconnect Failure Analysis in IConnect Impedance Accuracy TDR Multiple Reflection Effects Z Z 1 Z 2 Z 3 Z 4 V transmitted1 V reflected1 V reflected2 t Time Direction of propagation 12

13 Impedance Accuracy IConnect Computation of the True Impedance Profile V V V reflected 1 reflected 2 reflected 3 = ρ V 1 = t ρ V = 2 1 incident 1 2 incident 1 + ρ V 1 incident ( t1 t 2 ρ 32 t1 ρ 2 ρ 1 ) Vincident 1 + t1 ρ 2V incident 2 + ρ 1V incident 3 V V V V reflected1 reflected 2 reflected 3 M reflectedn k k = k M k n k k k 1 2 n 1 k k 1 n 2 L O L V V M V k V 1 incident1 incident 2 incident 3 M incidentn Impedance Accuracy Board Trace IConnect Z-line 13

14 Impedance Accuracy Package Trace IConnect Z-line Impedance Accuracy IConnect TDR Software Z-line Algorithm Ensures accurate impedance measurements Also called Impedance De-embedding, Peeling, Inverse Scattering Minimizes effects of multiple reflections Computes true impedance profile Enables model generation compute SPICE model output cursor readout for Z, td, L and C Limitations: data noise may interfere with accuracy use scope averaging use software noise filtering line loss may cause problems 14

15 Outline TDR Impedance Measurements in IConnect Interconnect Probing and Fixturing Quick Guide: Interconnect Probing Quick Guide Interconnect Signal Integrity Modeling and Model Validation in IConnect Interconnect Failure Analysis in IConnect Probing and Fixturing Probing and Fixturing Issues Probing is the weakest link! Start with a probe 5 Ohm for TDR measurements must be rugged and inexpensive ensure stable repeatable contact large pitch* means small bandwidth variable pitch means poor repeatability ensure sufficient compliance * Pitch: center-to-center signal to ground pad spacing 15

16 Probing and Fixturing Probe Bandwidth Selection Determine the required signal bandwidth BW =. 35 rise time t rise BW = 6 clock f cloc k BW = max( BW 3, BW DUT rise time clock ) Determine the required probe bandwidth BW > probe BW DUT Probing and Fixturing Package and Connector Probing Use a high-quality probe (and positioner) Need an interface adapter or fixture to probe Fixturing requirements Reproduce the real application environment Ensure easy fixture de-embedding (reference short and open structures may be needed) Vias to package leads Signal- Ground Probe Package PCB provides ground connections Fixture ground plane PCB provides ground connections PCB trace to package lead Package Fixture ground plane Via to ground for reference measurements 16

17 Probing and Fixturing Board Probing Ensure good contact to a via (via probing is a challenge for microwave probe) Ensure ground contacts near your signals Variable pitch is a sad necessity if there are no ground nearby TDR probes from TDR manufacturer Variable pitch probes from probe manufacturers Measurements suffer from poor repeatability and decrease the instrument usable bandwidth Probing and Fixturing Probing vs. Fixturing Probing advantages: Maximum flexibility for multiple device measurements No fixture de-embedding required But: Requires DUT to have easily accessible contact areas Positioning system may be expensive Fixturing advantages: Evaluate the DUT in its intended environment of use (example: package on a board) Great flexibility for specific DUT But: Difficult to change after the fixture has been designed Must de-embed fixturing from measurements! These approaches are complementary!! Fixturing is thinking ahead about how you will probe! 17

18 Outline " TDR Impedance Measurements in IConnect Interconnect Signal Integrity Modeling in IConnect IConnect TDR Software Modeling Methodology L and C Computation and Short Interconnect Analysis Single-ended TDR Transmission Line Modeling Differential TDR Coupled-Transmission Line Modeling Lossy Transmission Line Modeling Interconnect Failure Analysis in IConnect IConnect Modeling Methodology Goals and Model Validity Goal: create SPICE /IBIS models to predict interconnect performance Model required range of validity is defined by a greater of signal rise time: f bw =.35 / t rise It may be desired to extend the required range of model validity beyond f bw 18

19 IConnect Modeling Methodology How Will the Results Be Used? Simulate your I/O Bus from Driver to Receiver In SPICE or IBIS Predict signal integrity issues Jitter, loss, crosstalk, reflections, ringing # Optimize the Interconnect for best signal integrity IConnect Modeling Methodology Interconnect Models Lumped L Distributed C Z Mixed L Z C Coupled Z 1 Lossy L R Z 2 C G 19

20 IConnect Modeling Methodology Why Measurement-Based Modeling? Analytical model may differ from reality: Accuracy and assumptions of the analytical tool Material properties may not be available Geometries may not be available Component manufacturing tolerances Accurate measurement is the true representation of reality Analytical models must be validated with measurement Accurate models achieved through prototype characterization IConnect Modeling Methodology Measurement Based Approach TDR Measurements Extracted interconnect, TDR source model Direct link to simulators Automatic comparison of simulation and measurement in IConnect waveform viewer 2

21 IConnect Modeling Methodology Connector: Correlate Model to Physical Structure PCB section Cable section Partition 1 Partition 2 Package: Correlate Model to Physical Structure IConnect Modeling Methodology Package Board trace Board trace Bondwire Package Shelf Bondwire Die Pad Board Pad Package Model 21

22 IConnect Modeling Methodology TDR Measurement IConnect TDR Software IConnect SPICE / IBIS Simulation Package Board Field Solver Analysis Accurate validated models for interconnects IConnect Modeling Methodology Frequency or Time Domain? VNA: Steady state measurements Very high dynamic range Black box S- parameter results Single-element modeling capabilities TDR: Transient measurements Windowing capability Can model complex structures but multiple reflections impede accuracy 22

23 IConnect Modeling Methodology Frequency or Time Domain Interconnect properties Typically are complex multi-element structures Interconnects are broadband structures Measurements do not require high dynamic range Interconnects are NOT strongly resonant structures, 4dB dynamic range is sufficient Measurement DO require good spatial (time) resolution that TDR provides Summary: Use Time Domain as primary modeling tool Use frequency domain to model secondary effects IConnect Modeling Methodology Behavioral or Physical Model? Physical (TDR) Correlates to the interconnect geometry Allows to isolate the signal integrity issues TDR interconnect modeling Behavioral (VNA) Does not correlate to geometry Matches the frequency or time response VNA interconnect modeling Package Board trace Package Board trace Bondwire Package Shelf Bondwire Board Pad Die Pad Package Model Board trace Single-element model OR Behaviorial model OR S-parameters S S S21 S22 Physical model: correlates to the DUT geometry 23

24 IConnect Modeling Methodology SPICE or IBIS? Interconnect models are not substantially different in SPICE and IBIS You can create either models with TDR Main functional difference is in active component models (driver/receiver) You choice which to use for simulations Outline " TDR Impedance Measurements in IConnect Interconnect Signal Integrity Modeling in IConnect L and C Computation and Short Interconnect Analysis Appnote: TDR Techniques for Characterization and Modeling of Electronic Packaging Single-ended TDR Transmission Line Modeling Differential TDR Coupled-Transmission Line Modeling Lossy Transmission Line Modeling Interconnect Failure Analysis in IConnect 24

25 IConnect Short Interconnect Modeling Using a Lumped Model for an Interconnect t prop delay t rise Practical rule of short or lumped (RLC) interconnect t rise > t prop delay 6 IConnect Short Interconnect Modeling What Are Short Interconnects? Example: at 5ps rise time, the following interconnects can be considered short: IC packages Connectors Sockets Vias on the board 25

26 IConnect Short Interconnect Modeling Single Parasitic Inductance V R source TDR Oscilloscope Front Panel V incident Cable: Z, td V reflected L V ref short L V TDR 1 L = 2 t t 2 1 Z( t) dt = Z V t 1 ( V V )dt TDR ref short IConnect Short Interconnect Modeling Single-Ended TDR: Package Lead Inductance L Measurements TDR into the package lead Measure reflection Measure near-end crosstalk in adjacent lead Package leads TDR waveform: TDR into package lead. Short all the leads to ground on the inside of the package. Short the leads that are not being measured to ground on the outside of the package. Short waveform: TDR into the short ; connect the probe signal contact to ground on a conductive (metal) pad Package under test Short lead ends to ground W short L L Induced waveform: Measure near end crosstalk with far end of the victim openended Background waveform: Corrects for the noise and scope DC offset L W TDR V induced L mutual Z self = ( WTDR Wshort ) dt 2 V Z mutual = ( Winduced Wbackground ) 2 V V background noise dt 26

27 IConnect Short Interconnect Modeling Single Parasitic Capacitance V R source TDR Oscilloscope Front Panel V incident Cable: Z, td V reflected C Open V ref open C V TDR C = 1 2 t2 1 1 dt = Z( t) Z V t1 t1 ( V V )dt ref open TDR IConnect Short Interconnect Modeling Single-Ended TDR: Package Lead Capacitance C Measurements TDR into the package lead Measure reflection Measure near-end crosstalk in adjacent lead Package leads Package under test Keep lead ends open TDR waveform: TDR into package lead Short the leads that are not being measured to ground on the outside of the package Open waveform: TDR into the open ;disconnect the probe from the DUT or remove the DUT from the fixture W open C C C W TDR 1 self = ( Wopen WTDR ) 2 Z V Induced waveform: Measure near end crosstalk with far end of the victim openended Background waveform: Corrects for the noise and scope DC offset dt V induced C mutual V background noise 1 mutual = ( Winduced Wbackground ) 2 Z V dt 27

28 IConnect Short Interconnect Modeling Even-Odd Mode Impedance Profile Measure odd mode TDR with differential stimulus, and even mode TDR with common mode stimulus TDR into the two adjacent socket lead with differential and common mode stimulus Package leads Package under test self ( Z t Z t ) 1 L = + 2 L m = 2 1 even even odd odd ( Z t Z t ) even even odd odd C C tot m 1 t = 2 Z 1 t = 2 Z odd odd odd odd t + Z t Z even even even even C total = C self + C m IConnect Short Interconnect Modeling Inductance and Even-Odd Mode Measurements 28

29 IConnect Short Interconnect Modeling Adjacent-Opposite Mode Analysis Differential measurement of adjacent leads Package leads Package under test L total adjacent = L self L mutual L self = L total opposite L mutual = L total opposite -L total adjacent Differential measurement of orthogonal leads IConnect Short Interconnect Modeling Techniques for Various Packages SOIC TSOP PGA QFP Small BGA, LGA Large BGA, LGA MCM CSP Model required C L C L Distributed, coupled Distributedcoupled Distributedcoupled Distributedcoupled Distributedcoupled C L Primary modeling method Lumped Adjacentopposite Lumped Adjacentopposite Impedance profile Even-odd impedance Even-odd impedance Impedance profile Impedance profile Lumped Adjacentopposite Secondary modeling method Lumped Lumped Even-odd impedance Lumped, adjacent-opp. Lumped, adjacent-opp. Even-odd impedance Even-odd impedance Lumped 29

30 Outline " TDR Impedance Measurements in IConnect Interconnect Signal Integrity Modeling in IConnect Single-ended TDR Transmission Line Modeling Appnote: PCB Interconnect Characterization from TDR Measurements Differential TDR Coupled-Transmission Line Modeling Lossy Transmission Line Modeling Interconnect Failure Analysis in IConnect IConnect Single-Ended TDR Techniques Transmission line Z and t d Directly available from impedance profile Eliminate confusion about: exact impedance value exact electrical length of the lines Z 1 Z 2 t d 3

31 IConnect Single-Ended TDR Techniques Via L and C 1 t L = 2 Z( t) dt C = 2 dt Z( t) t1 1 t t1 t 2 t 1 t 1 t 2 IConnect Single-Ended TDR Techniques IConnect Modeling Process Measure and acquire Process data Extract model Simulate, compare and verify 31

32 IConnect Single-Ended TDR Techniques Modeling in IConnect TDR Software * Name: Automatically Generated.subckt Single port1 port2 gnd_ ****** Partition #1 c1 port1 gnd_ 456f l1 port n ****** Partition #2 t1 1 gnd_ 2 gnd_ Z=5.8 TD=125p.. ****** Partition #4 t3 3 gnd_ port2 gnd_ Z=48.2 TD=19p.ends IConnect Single-Ended TDR Techniques Prepare to Simulate and Validate 32

33 IConnect Single-Ended TDR Techniques Simulation and Validation Results IConnect Single-Ended TDR Techniques Using Rise Time Filtering to Achieve Simple Models 33

34 Outline " TDR Impedance Measurements in IConnect Interconnect Signal Integrity Modeling in IConnect Differential TDR Coupled Line Modeling Appnote: Characterization of Differential Interconnect from TDR Measurements Lossy Transmission Line Modeling Interconnect Failure Analysis in IConnect IConnect Differential TDR Techniques Coupled Line Models Predict: Differential line signal propagation Single ended and differential crosstalk Forward Backward Re-reflection Crosstalk-induced jitter 34

35 IConnect Differential TDR Techniques Differential Line Modeling Short interconnect use lumped-coupled model Long interconnect split lines in multiple segments Longer yet interconnect symmetric distributed coupled line model Z odd, t odd Z odd, t odd -Z odd /2, t odd Z even /2, t even IConnect Differential TDR Techniques Symmetrical Coupled Line Model TDR source 1 Board lines TDR source 2 Assumptions: the lines are symmetrical TDR pulses are symmetrical TDR pulses arrive at the lines at the same time at the beginning of both lines 35

36 IConnect Differential TDR Techniques Differential TDR Measurement Setup R source Cable: Z, td Z DUT, t DUT V V TDR Oscilloscope Front Panel V incident V reflected Cable: Z, td Z DUT, t DUT Z termination R source Z termination IConnect Differential TDR Techniques Even/Odd vs. Common/Differential Z odd = L C self tot L + C m m Z even = L C self tot + L C m m odd ( L L )( C C ) t = l + self m tot m t even = l ( L + L )( C C ) self m tot m Z differential = 2 t = t differential Z odd odd Z Z = common even t common = t even 2 36

37 IConnect Differential TDR Techniques Even and Odd Impedance Profile Example Z even >Z self >Z odd t even >t self >t odd Note: - odd mode = differential measurement (two TDR sources of opposite polarity) - even mode = common mode measurement (two TDR sources of the same polarity) IConnect Differential TDR Techniques L-C Even-Odd Mode Analysis for Line with Constant Impedance ( t Z t Z ) 1 L = + 2 even even odd odd C = t Z even even L m = 2 1 ( t Z t Z ) even even odd odd C m 1 t = 2 Z odd odd t Z even even 37

38 IConnect Differential TDR Techniques IConnect Symmetrical Coupled Line Model Z odd, t odd Z Z Z odd, t odd -Z odd /2, t odd Z even /2, t even Z odd, Z even, t odd, t even : directly obtained from odd and even impedance profiles IConnect Differential TDR Techniques IConnect Simplified Symmetrical Coupled Model Z Z Z Z mutual Z Z = Z even Z m Note: Z = 2 Z even Z = odd Z Z even odd Z odd Z even! assume: t odd =t even! Alternatively, for differential lines: t mutual = t odd 38

39 IConnect Differential TDR Techniques IConnect Differential Line Modeling IConnect Differential TDR Techniques Composite Model Generation * Name: Automatically Generated.subckt Symmetric ****** Partition #1 t Z=49.7 TD=92.3p t Z=49.7 TD=92.3p ****** Partition #2 l n c p l n c p c f k1 l1 l2 27m.ends 39

40 IConnect Differential TDR Techniques Model Validation in IConnect IConnect Differential TDR Techniques Coupled LC Computation in IConnect 4

41 Outline " TDR Impedance Measurements in IConnect Interconnect Signal Integrity Modeling in IConnect TDT, Lossy Line Modeling and Eye Diagram Appnote: Practical Characterization of Lossy Transmission Lines Using TDR Appnote: Ensuring Signal Integrity TDR and Frequency Domain Analysis Can Do the Trick Interconnect Failure Analysis in IConnect TDT and IConnect Lossy Lines Effect of Loss Decrease in amplitude Rise time degradation 41

42 TDT and IConnect Lossy Lines Rise time degradation t r signal BW interconnect t interconnect t r final t = interconne ct.35 BW interconnect t 2 2 r final = tr signal + t interconnect TDT and IConnect Lossy Lines Lossy Line Modeling DC resistive losses TDR loss R dc Skin effect losses R skin = R + R f s TDT loss TDR of ideal transmission line skin effect loss Dielectric losses G dielectric = G + G Dispersion d f t rise degradation dielectric loss 42

43 TDT and IConnect Lossy Lines Skin Effect vs. Dielectric Loss TDT and IConnect Lossy Lines IConnect Lossy Line Modeling Use TDT to extract losses directly from time domain measurement 43

44 TDT and IConnect Lossy Lines Compute Skin Effect, Dielectric Loss, RLGC(F) Extracted skin effect and dielectric loss parameters Simulated and measured transmission TDT and IConnect Lossy Lines Loss-Based Eye Diagram Degradation 44

45 Predicted and Measured Eye Diagrams Measured Simulated K28.5 Simulated PRBS TDT and IConnect Lossy Lines Lossy Line Modeling Measure TDT, compute S21 in IConnect 45

46 Outline " TDR Impedance Measurements in IConnect Interconnect Failure Analysis in IConnect Interconnect Signal Integrity Modeling in IConnect Application note: Electronic Package Failure Analysis Using TDR IConnect Failure Analysis TDR as a Failure Analysis Technique Cable TDR probe with signal and ground connections TDR Instrument Similarities with SAM and X-ray: Sends incident signal at the DUT Analyzes the reflection from the DUT 46

47 IConnect Failure Analysis TDR Differences from SAM and X-Ray Stimulus type TDR Electrical SAM Acoustic X-ray X-ray Stimulus delivery medium Direct contact required? Electrical wires Yes, signal and ground Water No Air No Output presented for analysis Ability to locate failures between package layers Package trace reflection profile Good Optical image Poor Optical image Poor IConnect Failure Analysis Opens and Shorts: IConnect FA Methods Signature analysis Comparative analysis Physical vs. Electrical Length Analysis Layer correlation analysis 47

48 IConnect Failure Analysis Signature Analysis: TDR and Impedance Profile V TDR Open >1 Ω Impedance Open 2 t cable 2 t cable ½ V 5 Ω TDR Short Ω Impedance Short IConnect Open Failure Analysis Open Signature Analysis 8 ps (16ps roundtrip) Failure is about 8 ps inside the package 48

49 IConnect Open Failure Analysis Open Comparative Analysis Failed trace waveform overlays directly over the substrate waveform. Conclusion: failure is due to package to-die connection IConnect Open Failure Analysis Physical Analysis, Parallel Lapping 49

50 IConnect Open Failure Analysis TDR Measurement Repeatability This is measurement repeatability issue This is the real failure location IConnect Open Failure Analysis Open Correlation Analysis Simplified package 1 trace geometry Ball Die Trace on layer 1 Via to die Simplified package 2 trace geometry Ball Die Package Via L=2nH Die input C C=8fF Trace on layer 2 Via to die 5

51 IConnect Open Failure Analysis Physical vs. Electrical Length Analysis Vprop average ltotal 1 = V t V C l = t d l t d total total d total IConnect uses ε r C t=45ps l=1mm V prop =4.5ps/mm =.74V C ε r =1.8 ε r average = V V c prop average 2 Vc t = l d total total 2 IConnect Short Failure Analysis Short Failure Analysis 51

52 IConnect Short Failure Analysis Short Failure: Impedance vs. Distance t=63ps l=8.7mm V prop =7.24ps/mm ε r =4.9 IConnect Short Failure Analysis Plane-to-Plane Shorts: Test Vehicle (TV) Typical probe placement 3" Top left probe point Vias to bottom plane Center left probe point Top plane Center probe point Bottom center probe point 1 3/8" (35mm) Bottom left probe point Bottom right probe point 52

53 IConnect Short Failure Analysis Plane-to-Plane Short TV Measurement IConnect Short Failure Analysis Plane-to-Plane Shorts TV Results 3" Top plane Vias to bottom plane left probe point Center probe point Bottom center probe point 1 3/8" (35mm) Physical expectations Left Center Right Top X 2 6 Center Bottom Electrical length results Left Center Right Top X 4 5 Center Bottom Inductance results Left Center Right Top X 3 4 Center Bottom

54 IConnect Short Failure Analysis Plane-to-Plane Shorts: Actual Package 1 Substrate 2 Good die 3 Bad (failing) DUT Substrate 4 ph Good die 6 ph Bad (failing) DUT 8pH IConnect Failure Analysis Signal to Signal or Plane to Plane Shorts Try differential TDR! R source Cable: Z, td V V TDR Oscilloscope Front Panel Virtual ground DUT: Z DUT V V reflected incident Cable: Z, td R source 54

55 Collateral Presentation Handouts Application materials TDR References Outline " TDR Impedance Measurements " Interconnect Failure Analysis " Interconnect Signal Integrity Modeling Discussion and practical session 55

56 Supplementary Information Transmission line equation reference Z = R G + + jwl jwc L C V p = 1 LC L = Z t p C = t Z p 56

57 Basic Stripline and Microstrip Equations w t Z = h ln ε w+ t r h Ground plane Dielectric, εr V p = ε for 1. < w / h < 2. 1< < 15 ε r r ns/ft h 1 Ground plane w Z 6 4 b = ln ε 67. π ( 8. w+ t) r b h 2 t V p = 117. ε r ns/ft Ground plane Dielectric, ε r for w / b < 35. t / b < 25. Propagation Delay Time required for signal to propagate through interconnect Dependent on velocity and interconnect length Examples: prop. delay in vacuum: 1/c light =1 ns/foot (velocity m/sec) propagation delay per length in FR4: 15ps/inch T prop delay = c light l ε eff Z, td, l (length) Propagation delay 57

58 Propagation Delay in Transmission Lines T prop delay = c light l ε eff = l LC C light is speed of light in vacuum (3 1 8 m/sec) ε r Microstrip ε eff depends on ε r of the board material and ε r of air for microstrip L, C are inductance and capacitance per unit length ε r Stripline Can You Ignore Propagation Delay? t prop delay t rise Practical rule of short interconnect t rise > t prop delay 6 58

59 Interconnect vs. IC Propagation Delay IC propagation delay decreases as the IC technology improves Interconnect delay depends only on the length and board material unless ε eff or length decrease, interconnect delays will stay constant T prop delay = c light l ε eff Reflections in Interconnects Interconnects are transmission lines Impedance is the measure of transmission properties of interconnects In any transmission media, at the impedance discontinuity part of the energy is reflected back V incident V reflected Z 1 Z 2 V transmitted Reflection coefficient: V Γ = V reflected incident = Z Z 2 2 Z1 + Z 1 59

60 Reflections Example: Long Interconnect 2 td tr = 1 ps Z, td, l (length) td = 8ps (~5 inches) Digital threshold switching and timing errors are likely Reflections Example: Short Interconnect tr = 2 ns Z, td, l (length) td = 3ps (~2 inches) Rarely a problem 6

61 Can You Ignore Reflections? t prop delay t rise Practical rule of short interconnect t rise > t prop delay 6 Ringing still may occur due to discontinuities (RLC) Crosstalk Energy coupling between adjacent lines Forward (far-end) and backward (near-end) Sum of capacitive and inductive R source Offender: Z 1, t d1 V Victim: Z 2, t d2 V R source V backward V forward 61

62 Forward and Backward Crosstalk Forward crosstalk (near end of the victim) proportional to rise time of the signal on offender proportional to the line length positive for capacitive and negative for inductive near zero for stripline = 1 Lm K f forward crosstalk constant = - C Z 2 m Z Backward Crosstalk not a function of rise time K b sum of capacitive and inductive = l Lm backward crosstalk constant = + C m Z 4 T Z prop delay Crosstalk Formation t V k T 1 T w g r T d V b1 V b2 f b t V f1 V f1 V f2 x 1 x 2 62

63 Crosstalk Observations Signal at the near end of the offending line t d Signal arriving to the far end of the offending line t 1-9 Derivative of the signal on the offending line (negative for dominantly inductive, positive for dominantly capacitive crosstalk Forward crosstalk at the far end of the victim line Total coupled areas are the same (provided only capacitive or only inductive crosstalk is considered) Backward crosstalk at the near end of the victim line 2 t d Rise and fall times are the same as the signal on the offending line Backward crosstalk for short and long line Long line case: 2T d >T 1 Short line case: 2T d <T 1 K b V k K b V k T 1 2 Td 2 T d T1 2 T d +T 1 2 T d 2 T d +T 1 63

64 Crosstalk Example R source Offender: Z 1, t d1 V 5 Ω Victim: Z 2, t d2 R source V V backward V forward Open Losses Skin effect losses R s g π µ = f P σ Ω inch Example (copper): g 7 R = f P - Ω inch Dielectric Losses G = g 2 π f ε tanδ d 64

65 Ground Bounce, or Simultaneous Switching Noise (SSN) IC Power IC I/O Buffer IC Ground Ground lead PCB Power Vcc lead Package lead L Package lead C SSN cause: inductance between IC, package and PCB ground SSN factors: signal rise time number of simultaneously switching buffers package inductance load capacitance PCB Ground Rise Time Degradation t = interconne ct.35 BW interconnect t 2 r final = t signal + t 2 interconne ct 65

66 Dispersion Signal integrity degradation due to pulse dispersion Typically not present strongly in megahertz signals 66