ESD

ESD Course

Dr. Lim Soo King

BSc (Hons)(Lond); Dip. Mgt (Dist)(MIM); MSc (Mal); PhD (Mal); MIPM

Associate Professor

ESD Course

Understand the phenomena of ESD.

Mechanism of ESD Process.

Identify ESD materials.

Ability to set-up the prevention and protection scheme for ESD occurrence.

Understand the ESD protection design for circuit.

Continuous improving process in ESD monitoring.

Be a trainer.

ESD Course

Outline of the Course

Introduction and Overviews

History.

ESD Failure Rate.

World Semiconductor Production.

Field Return Rate.

National Technology Roadmap for Semiconductor.

Picture Illustrating ESD Failure.

Evolution and Interpretation.

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Outline of the Course

Material properties.

Movement and discharge time.

Temperature and relative humidity.

ESD Course

Outline of the Course

Electrification.
Induction.
Gas discharge.
Chargeability.
Triboelectric series.
Causes of ESD .

Factors influencing static charge generation.

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Outline of the Course

How does static electricity damage a circuit?

Effects of ESD damage.

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Outline of the Course

Classification of ESD susceptibility.

Models of ESD reliability test.

ESD Course

Outline of the Course

Principles of Static Control.

Setting up ESD requirement production line.

Handling and storage of ESD sensitive parts.

Electrostatic protected area.

Good practice in ESD work area.

Audit.

ESD Course

Outline of the Course

Material structures and properties.

Criteria of selection.

Material design physics.

ESD Course

Outline of the Course

ESD materials.

Monitoring tools.

Prevention materials.

Protection materials.

ESD Materials Monitoring/Measurement

Tools and Awareness Label

ESD Course

Outline of the Course

Approach.

Methods employed for design protection and prevention.

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Outline of the Course

Case Study

Self audit.

Assessment

Twenty questions

.

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Introduction and Overviews

History.

ESD Failure Rate.

World Semiconductor Production.

Field Return Rate.

National Technology Roadmap for Semiconductor

Picture illustrating ESD Failure.

Evolution ad Interpretation.

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History

In 1400’s ESD procedure was installed to prevent electrostatic discharge ignition of black gun power in Europe and Caribbean.

In1860, it was used to prevent fire and during drying process in paper mill.

In modern world, ESD control is employed in many areas such as ship yard, paper

industry, assembly plant, microelectronics industry, and others.

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ESD Failure Rate

27 – 33 % 70 % 5 % User 8- 14 % 35 % 2 % Contractors 9 – 15 % 70 % 3 % Subcontractor 16 – 22 % 97 % 4 % Component Manufacturer Est. Avg. Loss Max. Loss Min. Loss Descriptions

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World Production of Semiconductor

0 50 100 150 200 250 '86 '90 '92 '94 '96 '98 '00 '02 '05 '06 Bil $

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Field Return Failure Mode

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National Technology Roadmap for

Semiconductor

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Picture of ESD Failure

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Picture of ESD Failure

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Picture of ESD Failure

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Picture of ESD Failure

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Evolution and Interpretation

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ESD is defined as electrostatic discharge.

It is a process of electron transfer between materials.

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Insulator is the main contributor of ESD.

It is a material that conducts very small amount of electricity.

Once the material loses or acquires electron, the electron equilibrium state remains for a long time.

Material loses electron has net positive charge.

Material acquires electron has net negative charge.

The most common way of generating static electricity is friction (contact and separate).

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Induction by EM interference causing polarization of

charge to other material at the polarized end. Example of such source is high tension terminal.

When two materials come in contact and separate,

static electricity will be generated.

When the charge material comes in contact with

another material, transfer of electron would occur resulting damage to the material.

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Transfer of Charge After Separation

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Generation of Static Charge by Separation

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Material properties.

Movement and discharge time.

Temperature and relative humidity.

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Material Properties

Conductor

Conduct good electricity. Low resistance.

No band-gap.

Semiconductor

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Material Properties

Moderate resistance. Narrow band-gap.

Insulator

Conduct very small amount or no electricity. High resistance

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Band-gap of Conductor

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Discharge Time Using Human Body Model

1013 Ω 1012 Ω 1011 Ω 1010 Ω 109 Ω Resistance 76.6 ms 9.2 ms 920 µs 2.0 µs 92 ns Time (ms) 2.5 hrs 920 s 92 s 920 ms 92 ms Time (ms) 108 Ω 107 Ω 106 Ω 103 Ω 102 Ω Resistance

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Movement time of Typical Operation

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Temperature and Relative Humidity

High temperature, high thermionic emission.

High relative humidity, more dissociation of water molecule, less charge generation.

Reduce surface resistivity.

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Typical Electrostatic Voltage at Different RH

1,500 250 100 600 1,200 1,500 35,000 12,000 6,000 7,000 20,000 18,000 Walking across carpet

Walking over vinyl floor Worker at bench

Vinyl envelope Poly bag

Chair padded with poly ethane foam.

65 – 90 % 10 - 20%

Means of Static Generation at Room Temperature

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Surface Resistivity versus RH at 25C

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Factors influencing static charge generation.

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Electrification

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The interface gap increased many folds.

Capacitance decreased many folds.

Potential difference between positively and

negatively charged layers increased tremendously.

Electric field is extremely high.

Neutralization tends to happen due to gas discharge.

Gas discharge if electric field is greater than 3 MV/m.

Neutralization depends on rate of separation, surface resistivity of material, temperature and humidity.

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Electrostatic Induction

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Electrostatic Induction

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Electrostatic Induction

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Electrostatic Induction

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Electrostatic Induction

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Electrostatic Discharge

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Inhomogeneous field gas discharges occur first

at the strongest part of the field when it is sufficient to cause an avalanche.

Small surface high electric field.

Breakdown of air closed to pointed electrode.

Glow is usually observed in dark caused by relaxation of atom from excited state with

emission of photons.

Violet color is nitrogen and red color is oxygen.

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Corona discharge.

Spark discharge.

Flash lightning.

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Corona Discharge

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Corona Discharge

Presence of electric field.

As the pointed needle is closed to charged

conductor, the electric field builds up.

Ionization (corona) occurs when reaches

critical field (3 MV/m).

Positive and negative ions generated.

Color visual light can be observed.

Micro-ammeter will register current.

Corona discharge can be occurred with applied

high potential to pointed needle.

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Demonstration of Corona Discharge

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Spark Discharge

Discharge between flat metallic electrodes.

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Chargeability Versus Surface Resistivity

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It determines how different materials compare with their

tendency to lose or acquire electron when one in contact and separation with another.

It is a table showing the order of charge type acquired by

the common insulating materials.

It is a prediction of the charge polarity.

If wool comes in contact with PVC and separate, wool

would lose electron and PVC would gain electron.

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Positive (donor) + Human hands Rabbit fur Glass Polyamide Nylon Wool Silk Aluminum Paper Steel Neutral 0 Cotton

Trioelectric Series

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Material with high relative permittivity tends to lose electron easier than material with low

relative permittivity.

High surface conductivity, less charge.

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Triboelectric -Relative Permittivity

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Typical Source of Static Generator in MFG Area

Waxed, painted or varnished

surface. Common vinyl or plastic. Sealed concrete or sheeting.

Synthetic personal garments.

Finished wood. Fiber glass. Plastic, bag, wraps, envelope, boxes, trays, bubble pack.

Spray cleaner, ungrounded solder iron, brushes, sand blasting, heat gun, temperature chamber, and etc. Work surface Floor Clothes Chair Packaging and handling Assembly Cleaning Test Repair

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Causes of ESD

Inadequate protection, prevention, and verification.

Too many static generators in work area.

Lack of proper training.

Lack of focus. i.e. no steering committee to handle ESD issue.

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Causes of ESD

Rapid flow of charge between two objects in contact.

Point of contact.

Surface resistivity.

Work function of materials.

Humidity and temperature.

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Factors Influencing ESD Generation

Material Type

Conductor - surface resistivity < 105_{/ . Too rapid discharge.}

Dissipative – surface resisitivity 106_{/ and 10}12_{/ . Moderate}

discharge.

Insulator – surface resistivity > 1012_{/ . Too long discharge.}

Integration Scale of IC’s

30 years ago 10-20 µm. Today is sub-micron.

Oxide thickness from 1000th _{Armstrong to less than 100}

Armstrong.

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Factors Influencing ESD Generation

Less electric field is required to damage oxide and active part.

Relative Humidity (RH)

High RH means more water. High water content means higher H+ _{and OH}- _ions.

Increase the surface conductivity.

Lesser tendency to lose or acquire electron.

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Factors Influencing ESD Generation

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How does static electricity damage a circuit?

Effects of ESD damage.

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ESD Failure Mechanism

Thermal secondary breakdown

Dielectric breakdown

Gaseous arc discharge/junction spiking.

Bulk breakdown.

Latent and catastrophic failure.

ESD upset – resulting soft bit.

I/O and functional failure.

Joule Heating.

Electrical overstress (EOS).

Dt AS E T π ρ

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Identifying of ESD Failure Mechanism

Initial test result – high leakage failure.

Functional test failure.

Pattern test failure.

Deviation of curve tracer results.

Before burn-in, LCD static analysis for hot spot.

After burn-in, high leakage failure at final test results.

Failure analysis to trace the failure site.

High power optical inspection.

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A Typical Set-Up to Measure Output High Leakage Current IOH

Positive current means possible transistor M₃ and M₄ have problem.

Negative current means possible transistor M₁ and M₂ have problem.

Most problem found at the gate, source of p-MOS or drain of n-MOS transistors.

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Layout of a Two-input NOR Gate

Source

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A Typical Set-Up to Measure Output Low Leakage Current IOL

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Layout of a Two-input AND Gate

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-30 -20 -10 0 10 20 30 40 50 -3.7 -3.5 -3 -2 -1 0 0.5 1 1.5 2 2.5 3 Good Bad

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Drain of n-MOSFET damaged by ESD causing leakage to p-substrate region.

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Metal 1 fused open and re-flowed/melted

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Effects of ESD Damage

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How does IC’s damaged by static

electricity?

Primary factor is transfer of charge between IC’s, which termed as discharge process.

Reduction in capacitance by lifting resulting damage due to increase of voltage.

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Failure Mechanism due to Transfer of

Charge

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Failure Mechanism due to Lifting

Capacitance is inverse proportional to separation of the capacitor.

If a device on the bench having a few hundred of volt of static charge and is not sufficient to

damage the circuit lifting by operator, the

reduction in capacitance resulting in increase of static voltage to several thousand voltage can instantly damage the device

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Classification of ESD susceptibility.

Models of ESD reliability test.

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Classification of ESD Susceptibility

It depends on the ESD failure model use.

The most susceptible class of product is MOSFET, TFT, GaAsFET, and others.

Schottky diode, Op-Amp, and MOS devices are moderate class.

Resistor chip, low power transistor, SiC devices are least susceptible.

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HBM Classification of ESD Susceptibility

≥ 8,000 V 3B 4,000 to < 8,000 V 3A 2,000 to < 4,000 V 2 1,000 to < 2,000 V 1C 500 to < 1,000 V 1B 250 to < 500 V 1A < 250 V 0 Voltage Range Class

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MM Classification of Product Susceptibility

> or = 400 V M4 200 < 400 V M3 100 to < 200 V M2 < 100 V M1 Voltage Range Class

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CDM Classification of Product Susceptibility

> 2,000 V C7 1,500 V to ≤ 2,000 V C6 1,000 V to ≤ 1,500 V C5 500 V to ≤ 1,000 V C4 250 V to ≤ 500 V C3 125 V to ≤ 250 V C2 < 125 V C1 Voltage Range Class

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ESD Failure Model

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Human Body Model

Involve at least two pins.

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Machine Model

Involve at least two pins.

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Charged Device Model

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Field Induced Model

Floating Induced Model

Presence of electric field damaging unprotected circuit without discharging.

Presence of electric field damaging floating gate.

Charged Board Model

Charged board damage is more severe than HBM or CDM due finger inductance and board capacitance.

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Ideal RLC Parameters of HBM, MM and CDM

500 V 5 nH 20 _Ω 10 pF CDM 500 V 750 nH 20 _Ω 200 pF MM 5 kV 7500 nH 1.5 k_Ω 100 pF HBM Voltage V Inductance I Resistance R Capacitance C ESD Model

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Prevention and Protection

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Principles of Static Control

Design in immunity.

Eliminate and reduce generation of static electricity.

Dissipate and neutralize.

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Setting-up an ESD Requirement Production

Line

Using ESDA S20.20, DOD-HBK-263B, JESD625-A,

Mil-std-1686A, and 883 method 3015.7 specifications as the guides.

Convert the requirements into own internal

specifications.

Generate audit check sheets and records.

Set-up a ESD Steering Committee

A cross functional team ideally headed by QRA.

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Setting-up an ESD Requirement Production

Line

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ESD Safe Workstation

Grounding either hard ground and soft ground.

Conductive flooring/dissipative flooring.

Ground strap.

ESD garment such as finger cot, attire, and shoes.

Dissipative table mat and non-static generating

materials.

Localized ionization.

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Device/PCB Protection

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Protect the edge connector of the PCB with conductive

shunting bar.

Transport the device/PCB in shielded bag/Faraday cage.

Personnel Protection

Always wear a ground strap or ESD footwear before

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Always wear ESD protective smock.

Warning and Awareness

ESD warning signage at the entrance to ESD work area.

Training

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Awareness and re-training.

Constant update of ESD knowledge.

Audit

Ensure periodic audit.

Daily check the functionality of ground strap.

Certification and re-certification of personnel for ESD

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Typical Facility Areas Requiring ESD

Protection

Receiving.

Inspection.

Stores and warehouse.

Assembly.

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Typical Facility Areas Requiring ESD

Protection

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Good Practices in ESD Work Area

Always ground yourself by wearing a ground strap.

Keep away ESD generator from the device/PCB. e.g. paper, high tension terminal, plastic, and

etc.

Always use ESD workstation and wearing ESD attire.

Use shielded box or “low charge generation” tube to store or transport device/PCB.

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Good Practices in ESD Work Area

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Material structures and properties.

Criteria of selection.

Material design physics.

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Material Properties and Structures

Insulator.

Conduct little electricity.

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Resistance and Resistivity of Materials

Insulative 1.0x1012 Insulative Static Dissipative 1.0x106 1.0x107 1.0x108 1.0x109 1.0x1010 1.0x1011 Static Dissipative Conductive 1.0x103 1.0x104 1.0x105 Conductive Surface Resistivity (ΩΩΩΩ/□) ASTM D257 Value

Surface Resistance (ohm) S11.11.1993

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How to Interpret Surface Resistivity?

Surface resistivity (SR) is measured in Ω/□. It is the same irrespective of the square area.

People tend to measure SR using a normal resistance meter and probe, which is wrong.

SR should be measured using mega-ohm meter and square contact as provided in ASTM D257 and S11.11.

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How to Interpret Surface Resistivity?

If a 10 Ω resistance has a square surface. We say

the resistance is 10 Ω and SR is 10 Ω/

□

If two similar resistors are connected in series then the resistance is 20 Ω and the SR is not 20 Ω/

□

If two of these two resistors are connected in parallel then the effective resistance is 10 Ω and SR is 10

Ω/

□

This example illustrates that SR is same irrespective

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Criteria for Selection of ESD Materials

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Material Design Physics

Turning insulator into having antistatic properties.

Antistatic surfactant such as ethoxylated amines or ethoxylated ester mixed with polymer.

Commonly known as pink poly.

Conductive filler such as carbon black, carbon fiber, stainless-steel fiber, and etc mixed with polymer.

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Material Design Physics

Antistatic surfactant Carbon-filled polymer

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Material Design Physics

Surface resistivity comparison for various techniques

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ESD materials.

Monitoring tools.

Prevention materials.

Protection materials.

ESD Materials, Monitoring/Measurement

Tools and Awareness Label

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Common ESD Control Materials in ESD

Work Area

Personal grounding.

Protective clothing/smock/shoes.

Dissipative table mat.

ESD chair.

Conductive box/bag.

Conductive foam.

Antistatic tube.

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Common ESD Control/Monitoring Materials

in ESD Work Area

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Ground Strap

Physical Appearance Internal construction with Human body model

2.0 kV ESD voltage generates 1.3 A current without ground strap. 2.0 kV ESD voltage generates 2.0 mA current with ground strap. Discharge time – 150 µµµµs without ground strap.

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ESD Smock

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Static Dissipative Bag

Low static generator (antistatic) “pink poly”

polyethylene type, which is low-end ESD bag.

Carbonate non-transparent conductive bag.

Static shielding bag (Faraday shield) has a aluminum

coating deposited on polyester film outer layer and inner polyethylene layer.

Metal in has high resistance and metal out has lower

resistance.

Moisture Vapor Barrier shielding bag has 10X

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Static Dissipative Bag – A Typical

Construction

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Static Dissipative Mat

Volumetric type-Homogeneous

Non constant discharge time. Difficult to ground.

Cheap.

Ideal for service not for production.

Conductive type – Non-Homogeneous

Constant discharge time. Easy ground.

Costly.

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ESD Symbols

Ground Point Symbol ESD Susceptibility

Symbol

ESD Protective Symbol

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ESD Chair

The ESD Chair is designed

conductive materials.

hooded static-free casters.
static-free fabric material.
comfort

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Ionizer

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Ionizer – A dc Type

Corona discharge depends on curvature of the electrode.

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Shoes/Shoes Strap

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ESD Monitor Equipment

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ESD Monitor Equipment – Charge Plate

Discharge time measurement.

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ESD Monitor Equipment – Faraday Cup

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Approach.

Methods employed for design protection and prevention.

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Approach

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Field strength of silicon dioxide is 109

volts/meter. A device of oxide thickness 500 Armstrong, it needs only 50 volts to destroy the oxide.

The typical diode avalanche voltage is 5 V to 20 volts.

Junction breakdown for JFET and MOSFET is typically 20 V.

Electrical Strength of Semiconductor

Material

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Circuit Design Protection

Resistor

Limiting current and provide voltage drop.

Diode

Low resistance large current handling capability to bypass charge.

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Circuit Design Protection

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Resistor - Diode Circuit

Resistor R – 1.5 ΩΩΩΩ shall cause voltage drop.

Positive ESD bypassed through diode D₁.

Negative ESD bypassed through diode D₂.

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Thickness Field Oxide Device

Operate like a lateral npn transistor.

The drain space determines the maximum current

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n-MOS Pull Down Model

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Point 1, avalanche begins.

Point 2, snapback occurs. The lateral npn transistor is self-Biased mode.

Point 3, heating up of drain-substrate causes secondary breakdown exceed junction temperature.

Triggering Graph of Lateral

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Triggering Graph of Silicon Control Rectifier

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ESD/EOS standard.

Compliance.

Own specifications.

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ESD Compliance Specifications

DOD-HBK-263 B, JESD625-A, Mil-std-1686A, and 883 E method 3015.7 are sufficient.

ESDA S20.20 is sufficient to industrial standard.

The spec. covers many areas of control.

Design immunity, ESD susceptibility, and classification.

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ESD Compliance Specifications

Control and prevention.

Qualification and acceptance of new equipment and materials.

Testing circuit including ESD classification tests.

Auditing.

Training.

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