1. ESD Failure Analysis, Detection, and Simulation
Ray Nicanor M. Tag-at
iNARTE: ESD NE HGST Phil. Corp, a Western Digital Company

2. Course Outline Systematic Approach in ESD Auditing
Failure Mode Identification
Process Benchmarking
ESD Assessment
Perform Measurements
This will be the outline of presentation.
Modeling and Simulation
ESD Control Conceptualization

3. Course Outline Systematic Approach in ESD Auditing
Failure Mode Identification
Process Benchmarking
ESD Assessment
Perform Measurements
Modeling and Simulation
ESD Control Conceptualization

4. Failure Mode Identification
Product Failure Analysis and Characterization
This will confirm if indeed the failure is due to ESD or EOS, and not mechanical , contamination, or other defects.
The severity of the failure will somehow provide some clues as to the source/s of ESD or EOS.
In case you encountered ESD-related failures in your device, and if you have the capability, the 1st step is to identify and characterize the failure mode. Usually device that failed due to ESD are melted or have burn marks. The severity of this failure will give us some ideas on the possible source of ESD.

5. Failure Mode Identification
Product Failure Analysis and Characterization
ESD or EOS?
Electrical Overstress (EOS) and ESD have almost the same failure mechanism but differs on the sources.
ESD  Static or Transient
Sources:
The very fast (nano/picoseconds) ESD pulses.
Low energy
Often very small physical damage signatures
Some of us usually use ESD or EOS interchangeably when we encounter failure that shows burnt or melting. But what is actually the difference between ESD and EOS? EOS and ESD differs on the sources, but the failure signature is almost the same. Let’s explore further the differences. On ESD, from the word itself, it means the source is static charge. It’s a very fast transient with low energy, often around 1nJ, that is enough to cause physical damage to the device.

6. Semiconductors (CMOS Capacitor) Magnetic Heads (GMR/TMR)
Failure Mode Identification
Product Failure Analysis and Characterization
ESD or EOS?
ESD Damage
Direct ESD  HBM, MM, and CDM
Direct ESD happens when there’s a discharge path.
Severity of damage depends on the source of ESD.
Semiconductors (CMOS Capacitor)
There are two classifications of ESD damage. One is due to direct ESD, which comes from either HBM, MM, or CDM ESD events. This happens when there’s a direct discharge path to or from the device. The severity of the damage will depend on the magnitude of the source, it may be small or gross damage.
Magnetic Heads (GMR/TMR)

7. Failure Mode Identification
Product Failure Analysis and Characterization
ESD or EOS?
ESD Damage
ESD from Within  Field Induced Model (FIM)
ESD happens within the device itself by mere exposure to the electrostatic field.
Magnetic Heads (TMR)
The other one is called the ESD from within. There is no discharge path to or from the device, but ESD occurs inside the device. This happens when the device is exposed to a strong electrostatic field. Since components inside the device have different capacitance due to different areas, there will be a potential difference and dielectric breakdown between component can occur, causing ESD damage.
Good
Damaged
Damaged

8. Failure Mode Identification
Product Failure Analysis and Characterization
ESD or EOS?
EOS  Dynamic or Continuous
EOS failure is the result of "long" duration stress events (millisecond duration or longer).
For electrical overstress or EOS, the source is dynamic…could be pulsed, DC, or AC signal. It is often the result of a long duration of stress events, such as over voltage or over current, applied to the device.
A device is electrically stressed over it’s specified limits in terms of voltage, current, and/or power/energy.

9. Failure Mode Identification
Product Failure Analysis and Characterization
ESD or EOS?
EOS Damage
EOS damage is often the result of the high temperatures experienced during the EOS event.
External
Visible bulge in mold compound
Physical hole in mold compound
Burnt/discolored mold compound
Cracked package
EOS damage is somehow similar to that of the ESD, though a bit bigger in magnitude. It is often the result of high temperatures during EOS event, causing melting or burning. Here are some of the external damages of the device due to EOS.

10. Failure Mode Identification
Product Failure Analysis and Characterization
ESD or EOS?
EOS Damage
Internal
Melted or burnt metal
Carbonized mold compound
Signs of heat damage to metal lines
Melted or vaporized bond wires
And here are some of the internal damages to the device due to EOS. Notice the magnitude of the damage.
Melted TMR

11. Failure Mode Identification
Product Failure Analysis and Characterization
ESD or EOS?
Indications of EOS
Failure signature from excessive load dump.
Transistor failure of the emitter region of the die
Fused wire bond.
Metallization run on Op-Amp IC
Here are some of the indications of EOS. These are typical signatures due to excessive load dump or excessive bias voltage or current applied.
*images courtesy of

12. Failure Mode Identification
Product Failure Analysis and Characterization
ESD or EOS?
Indications of EOS
Failure signature from repetitive thermal cycling combined with high current.
Severely degraded
recrystalized metal (≥400ºC)
Other indication of EOS is recrystalization of the material due to thermal cycling. Meaning, the bias voltage or current applied in intervals, allowing the material inside the device to melt then hardened or crystallized once the bias goes off, then melt again as the bias is reapplied.

13. Failure Mode Identification
Product Failure Analysis and Characterization
ESD or EOS?
Possible Causes of EOS
Uncontrolled voltage surge on the power supply or testers.
Voltage spikes due to internal PCB switching.
Voltage spikes due to an external connection –capacitive charge on an external cable, antenna pick-up of external switching noise, inductive loads.
Poor grounding resulting in excessive noise on the ground plane.
Overshoot or undershoot during IO switching.
EMI (electromagnetic interference) due to poor shielding in an electrically noisy environment.

14. Failure Mode Identification
Product Failure Analysis and Characterization
ESD or EOS?
Summary
Distinguishing between ESD and EOS failures has always been of interest to failure analysts.
Since ESD and EOS failure attributes depends on the following:
nature of the electrical stress
circuit design
die lay-out, and
fab process used
It would be difficult (if not impossible) to come up with a catch-all manual to distinguish between EOS and ESD failures.

15. Course Outline Systematic Approach in ESD Auditing
Failure Mode Identification
Process Benchmarking
ESD Assessment
Perform Measurements
Modeling and Simulation
ESD Control Conceptualization

16. Process Benchmarking Process Mapping/Traceability
This will help in narrowing down the area to be audited.
The next step is to provide the list of processes the device undergo, by checking the failed device’s traceability. Here you can create a map, and identify which of the process or tool you suspect to be of high ESD-risk. You can also look for any tool/line or process dependency. This approach will help you in narrowing down the area to be audited.
Highlighted are the ESD-potential processes or tools.

17. Process Benchmarking What to Look For in an Identified Process?
Process Mapping/Traceability
What to Look For in an Identified Process?
High-powered tools  motors, transformers and HV power supplies, etc.
Tools with pneumatics/mechanical movement or AC switching  source of EMI.
Before doing any measurements, how can the high ESD-risk process in the map be identified? Well, simply look for the following: [click] High-powered tools -> this is a possible source of electrical noise and transients. [click] Look for tools with pneumatics, mechanical movements, or those with AC switching, as these are possible sources of electromagnetic interference or EMI. [click] You can also check for tools with direct metal contact or probing to the ESD sensitive device, as these can cause machine model (MM) or charged device model (CDM) ESD events.
Tools with direct metal contact or probing to the ESDS.

18. Process Benchmarking Process Partition Experiment
Whole Line/Fab ESD Partition Assessment
Aside from process mapping, process partition experiment can also be done. Here, the identified processes are being divided or partitioned into different segments. After each segments, parametric testing of the device’s performance is done. This will determine which process/tool causes ESD failures. Statistical analysis can also be done to determine symptoms of degradation or latent failures.
Processes are being divided into different segments.
ESD parametric testing is being done after each segment.
Done to identify which process/es causes ESD failures.

19. Process Benchmarking New Tool/Process Split ESD Parametric Analysis
Process Partition Experiment
New Tool/Process Split ESD Parametric Analysis
You can also perform the so-called split ESD parametric analysis. This is used to determine the ESD performance of a new tool or process. Split analysis means the samples are from the same group or batch and split equally. Statistical analysis is done on the results of the ESD parametric testing. The purpose of which is to simply eliminate the bias of the samples.
ESD parametric test is done initially for the samples. This will serve as the baseline data.
Samples are then split into equal parts. Experiment is then performed.
ESD parametric test is then conducted and compared to the baseline data.

20. Course Outline Systematic Approach in ESD Auditing
Failure Mode Identification
Process Benchmarking
ESD Assessment
Perform Measurements
Modeling and Simulation
ESD Control Conceptualization

21. ESD Assessment
Assess what are the ESD events that the identified process might contribute.
Probability of Occurrence
High
After identifying which process/tool that causes ESD failure, the next step is to assess what are the ESD events present in the said process or tool. This will later guide us in identifying the measurements to be done. The diagram shows the probability of occurrence of the ESD events. In an automated or semi-automated process with less direct handling to ESD-sensitive devices, Machine Model ESD event has the highest probability to occur. Followed by CDM. These two are simply due to the metal contact to the ESD sensitive devices. Field Induced Model is rated higher than HBM since FIM can be a preceding event to CDM, which we often refer to as Field-Induced CDM. This can happen when highly chargeable material is present near the device with metal contact to the tool.
Low
Note: This model is applicable to automated lines with less direct handling to ESD-sensitive devices.

22. ESD Assessment Recommended Measurements ESD Events Measurements
Category
Parameters
Method
Machine Model (MM)
Static: - Non-powered Tools - Powered Tools But No Probing to ESDS
Voltage
Static Charge Build-up
Electrometer
Current
Transient Noise
Tap Transient (CT-6)
Ground Noise
Continuous Measurement (CT-6)
Dynamic: - Testers - Powered Tools With Direct Probing to ESDS
Signal Analysis
Differential Voltage
Ground Noise Measurement at the Probes (Static and Dynamic Mode)
Tap Transient (Standby Mode)
H-Fields
EMI Check
EMI Sensor  During Actual Testing/Probing
Here are the recommended measurements once the ESD events have been assessed and identified. For the machine model, static or dynamic measurements can be done. Static measurements are applied to non-powered tools or tools with no probing to the ESD sensitive devices. The static charge build up, in voltage, can be measured using electrometer, and in current, using CT-6. Dynamic on the other hand is used for testers or tools with direct probing to ESDS. The tester’s bias voltage can be measured, differentially, for signal analysis. While the current can be measured either dynamic for ground noise or tap transient for static charge. Lastly, Electromagnetic interference or EMI can be checked when doing testing to the device.

23. Charged Device Model (CDM)
ESD Assessment
Recommended Measurements…cont’d.
ESD Events
Measurements
Category
Parameters
Method
Charged Device Model (CDM)
Resistance
Material Resistance Check (High  Charge Generation/Inhibition of Charge Dissipation)
MOM
Ground or Discharge Path
DMM
E-Fields
Static Field Charge Check (FIM)
Fieldmeter/Charge Plate Analyzer
Point Charge Check
Nanocoulomb Meter
Voltage
Tribocharge Check (Handling/Process/Operation)
Electrometer
Unbalanced Ionizer
Electrometer/CPM
Current
CDM Discharge Current
Tap Transient (CT-6) to the device
For CDM events, you can measure the resistance of the materials with direct contact to the device. High resistance inhibits the device’s charge dissipation, while low resistance materials can be a discharged path of the device. Electric fields from nearby insulative materials should also be measured to assess if these can induce charge to the device. Lastly, you have to perform a simulated discharge path to the device through tap transient method using CT probe to determine if indeed the device is charge and can discharge.

24. Course Outline Systematic Approach in ESD Auditing
Failure Mode Identification
Process Benchmarking
ESD Assessment
Perform Measurements
Modeling and Simulation
ESD Control Conceptualization

25. Perform Measurements Voltage Static – From electrostatic charge.
- The difference in electric potential between two points.
Static – From electrostatic charge.
The next step after ESD assessment is to execute those measurements. Let’s discuss first the voltage measurement. Voltage is often referred to as the potential difference between two points. The two states of measurement are Static, which is voltage from electrostatic charge, and dynamic, which is the potential from constant voltage sources.
Note: Electric potential at a point is the amount of electric potential energy that a unitary point charge would have when located at that point.
Dynamic – Potential from constant voltage sources such as testers or power supplies.

26. Perform Measurements Voltage Measuring Equipment and Probes Voltage
Digital Oscilloscope
Voltage Active Differential Probe
Single-Ended Voltage Active Probe
Here are some of the advanced voltage measuring tools, such as the high bandwidth oscilloscope, which can be used in conjunction with either the differential probe or the single-ended active probe, and electrometer, which can be used in measuring static voltage or charge using the triax probe.
Keithley 6517A Electrometer
Electrometer Triax Probe

27. Voltage Measurement - Dynamic Voltage Device Under Test (DUT)
Perform Measurements
Voltage
Voltage Measurement - Dynamic Voltage
Active Differential Probe and Oscilloscope
Source (I) +/- Electronics
Device Under Test (DUT)
For the dynamic voltage measurement, a differential probe can be used in measuring the bias voltage of the tester. It is connected differentially into the probe pins that injects the signal to the device and let the actual testing run. The waveforms shown are the measured bias voltage. The upper waveform is the normal bias voltage while the lower one is a bad signal. In here, one can check if the signal has noise, glitch, or overvoltage, that can cause electrical overstress or EOS.
To Oscilloscope
Voltage Active Differential Probe
Measures the differential voltage between the channel that injects signal to the DUT.

28. Perform Measurements Current
- Flow of electric charge.
- Energy sensitive devices are damaged by excessive current.
Static – Transient current from electrostatic charge / discharge.
Current is often defined as the flow of charge when voltage is applied across. There are also two states in measurement, namely the static, which measures transient current from electrostatic charge or ESD, and the dynamic, which measures the leakage current from tools or machines, as well as the high frequency noise from the testers.
Dynamic
– Current leaks from tools, machines, or equipment. Can cause ground noise.
– Noise or glitch from HF signal of testers.

29. Perform Measurements Current Probes Current Tek CT-1 and CT-2 Probes
Tek CT-6 Probe
Here are some of the probes used in current measurements. These are the current transformers, and only measure AC or high frequency signals.
Note: The concept of CT is converting the electric field from the conductor and converting it into the voltage of the oscilloscope. Transformation ratio is used to calculate the current from the voltage value.

30. Current Measurement - Static Simulated Device’s Resistance
Perform Measurements
Current
Current Measurement - Static
Tap Transient
MM Transient Wave Form
Simulated Device’s Resistance
To Oscilloscope
CT-6 Probe
Voltage (100 mV/div)
Source (I) +/- Electronics
One way of checking fast ESD transients is through the use of a CT current probe. The tap transient method uses a simulated device’s resistance connected in series to the CT probe and to the ground. The resistance simulates the actual current that flow to the device. The other end of the probe is tapped into the tester or metallic tools using the single shot mode of the oscilloscope. The waveform shown is a typical MM transient.
Tester or metallic tool with electrical circuits/motors
Time (50 ns/div)
Simulated device’s resistance.
Tap Transient Testing for static measurement, at single shot mode.

31. Current Measurement - Dynamic
Perform Measurements
Current
Current Measurement - Dynamic
Continuous Ground Noise Measurement
Noise Propagation from the Ground to the Jigs/Fixtures.
Jigs/Fixture
Current Waveform
CT-6 Probe
Tool/Machine
The CT probe can also be used to measure the noise from the ground line of the metallic jigs/fixture. The CT is connected in series to the ground and the dynamic measurement is done using the Norm Mode of the oscilloscope. The waveform shown here is dynamic and continuously oscillates. Again, note that only high frequency signals (shown in the waveform) can be measured using the CT.
Peak Current: 10.7 mA
Freq: MHz
Continuous Transient Testing for at dynamic condition, using Norm mode.

32. Device Under Test (DUT) Probe Pins (Dipole)  acts like antenna
Perform Measurements
Fields (E-Field and H-Field)
Voltage/Current Transients = E-field
Device Under Test (DUT)
Source (I) +/- Electronics
Transients from ESD or any AC switching can generate electromagnetic interference or EMI. EMI can cause failure to the device when there’s an antenna-effect, wherein wires connected to the device and to circuits pick-up the fields. The EMI-induced current will directly flow into the device, causing damage. Aside from damaging the device, EMI can also upset electronics circuits causing error in machines and robots. It can also cause noise in the measurements, especially during testing of the device.
Probe Pins (Dipole)  acts like antenna

33. Antenna Connected in Digital Oscilloscope
Perform Measurements
Fields (E-Field and H-Field)
Field Probes
Antenna Connected in Digital Oscilloscope
3M (Credence) EM Aware
Here are some of the field probes available in the market today. These are usually used in detecting the presence of an electric field or EMI. A customized dipole antenna, shown here, when connected to oscilloscope, can also be used to detect EMI.
Novx 7000
Sanki EMI Locator

34. Course Outline Systematic Approach in ESD Auditing
Failure Mode Identification
Process Benchmarking
ESD Assessment
Perform Measurements
Modeling and Simulation
ESD Control Conceptualization

35. PSPICE Modeling and Simulation
Simulation Program with Integrated Circuit Emphasis
General-purpose circuit program that simulates electronic circuits.
Used to perform various analyses:
time-domain response
frequency response,
operating points or transistors, and so on.
After doing the ESD measurements, the next step in the audit is to do modeling. This modeling helps one to understand the components present in the tool, machine, or process.

36. PSPICE Modeling and Simulation
PSPICE on ESD
Mostly, the Transient Analysis is being used in ESD Simulation.
Done to understand the sources and behavior of ESD, and determine how to control the sources.
Transient Analysis:
Used for circuits with time-variant sources (AC or switched DC sources)
Calculates all node voltages and branch currents over time interval.

37. PSPICE Modeling and Simulation
Transient Analysis…cont’d.
Voltage Sources
Pulsed Voltage Source
PSPICE Model

38. PSPICE Modeling and Simulation
Transient Analysis…cont’d.
Voltage Sources…cont’d.
Sinusoidal Voltage Source
PSPICE Model

39. PSPICE Modeling and Simulation
ESD Events Simulation – Transient Analysis
Human Body Model (HBM)
Machine Model (MM)
Charge Device Model (CDM)
HBM Simulated Circuit
CDM Simulated Circuit
MM Simulated Circuit
Run PSPICE 

40. Course Outline Systematic Approach in ESD Auditing
Failure Mode Identification
Process Benchmarking
ESD Assessment
Actual Measurements
Modeling and Simulation
ESD Control Conceptualization

41. ESD Control Conceptualization
Key Considerations
Elimination of the HF voltage/current source
Current Suppression
Current Diversion
Now for the ESD Control Conceptualization. The following are the key considerations in controlling the ESD transient current: 1) eliminate the source as much as possible, 2) suppress the current if the source could not be eliminated, or 3) divert the current away from the ESD sensitive device.
Run PSPICE 

42. Thank You!

43. Back-up

44. Discussion How to start the simulation?
Basic PSPICE Simulation
How to start the simulation?
Simulation should be based on the actual condition.
Prior ESD measurements should be made.
Transient Noise Measurements
RLC components identification.
L = 20 nH per inch of ground wire
C for charge storage
Power source consideration.

45. Discussion Actual PSPICE Simulation
PSPICE Simulation Workshop
Actual PSPICE Simulation
Understanding HF Noise from stepper motors, transformers, HV sources, etc.
Charge Decay Simulation (Spot Decay Test Using CPM)
Tools and series resistance