electro static discharge awareness and control an extensive course on

ELECTRO STATIC DISCHARGE ELECTRO STATIC DISCHARGE

AWARENESS AND CONTROLAWARENESS AND CONTROL

An extensive course on

Examples :

Lightning

Zapping

An atom is made up of charges

An atom is made up of charges.

In its stable state, the size of the positive charge at the centre (nucleus) of an atom is balanced by the size of all the negative charges of the electrons, making it neutral overall.

The electrons whirl around the centre like planets.

Creating a charge imbalance

When an atom loses an electron, it has a charge imbalance.

Since this atom has lost an electron, which is a negative charge, the atom is now a positive charge.

When it gains an extra electron, an atom becomes a negative charge.

Electron “lost”

A discharge

This movement of charges is called a discharge.

When something which has When something which has a charge imbalance is a charge imbalance is brought close to or touches brought close to or touches something else, a stream of something else, a stream of charges might move, to try charges might move, to try to bring the atoms back to to bring the atoms back to their stable balanced their stable balanced condition.condition.

This powerful, rapid movement of charges can damage electronic

components.

Let’s see it again!

WHAT IS ESD?WHAT IS ESD?

ELECTRO STATIC DISCHARGE IS DEFINED AS THE

TRANSFER OF ELECTRO STATIC CHARGES

BETWEEN BODIES AT DIFFERENT POTENTIAL

CAUSED BY DIRECT CONTACT

OR INDUCED ELECTRO STATIC FIELD..

ESD EVENTESD EVENT

IT IS AN UNPLANNED OCCURANCE OF ELECTRO- STATIC

DISCHARGE

What is ESD—Electrostatic What is ESD—Electrostatic Discharges (ESD) are the most Discharges (ESD) are the most severe form of Electromagnet severe form of Electromagnet Interference (EMI). The human body Interference (EMI). The human body can build up static charges that can build up static charges that range up to 25,000 volts. These range up to 25,000 volts. These build-ups can discharge very rapidly build-ups can discharge very rapidly into a electrically grounded body, or into a electrically grounded body, or device. Placing a 25,000-volt surge device. Placing a 25,000-volt surge through any electronic device is through any electronic device is potentially damaging to it.potentially damaging to it.

Moving people

Improper grounding

Unshielded cables

Poor connections

Moving machines

Low humidity (hot and dry conditions)

The most common causes of ESD are:

Figure 13-14: Power Transmission System

Figure 13-15: Grounds on IC Chips

Some devices used to remove solder from circuit boards and chips can cause high static discharges that may damage the good devices on the board. The device in question is referred to as a solder-sucker, and is available in antistatic versions for use with MOS devices.

To avoid damaging static-sensitive devices, the following procedures will help to minimize the chances of destructive static discharges:

Triboelectric generation

Basic Principles (2)

When two materials are in intimate contact, they share electrons which are at their surfaces.

When materials are in contact

The triboelectric charge of two materials in contact.

When two materials are in intimate contact, they share electrons which are at their surfaces.

When materials are in contact

It is possible for electrons to be “stolen” from one material by nuclei in the other material, because they

have a stronger force

When these materials are separated, electrons are removed from one material and are transferred to the

other material.

When the materials are separated

Electrons “lost”

Electrons “gained”




When these materials are separated, electrons are removed from one material and are transferred to the

other material.

This action takes place with all types of materials. With insulators, the charges remain at the points of contact. A charge spreads all over an ungrounded conductor.

The triboelectric charge when two materials placed in contact are then separated.

This action takes place with all types of materials. With insulators, the charges remain at the points of contact. A charge

spreads all over an ungrounded conductor.

When the materials are separated Electrons “lost”


The loss and gain of these electrons creates an imbalance of negative and positive charges on the

surface of each material.




When the surfaces are rough, this intimacy and separation is assisted by rubbing the materials together.




The size of the charge (imbalance) depends on the intimacy of the contact, how fast they were separated, the humidity and the kinds of materials




The drier the air (lower relative humidity, RH) the higher the generated charge

The creation of a charge when materials are separated is termed “triboelectric charging”

Charging by Induction

Basic Principles

Charging by induction

The presence of this very strong force causes The presence of this very strong force causes similar charges on the surfaces of nearby similar charges on the surfaces of nearby

conductors to be repelled.conductors to be repelled.

The charge imbalance on a surface produces The charge imbalance on a surface produces an electric field.an electric field.


If the conductor is grounded while it is still If the conductor is grounded while it is still influenced by the electric field, these repelled influenced by the electric field, these repelled charges go to earth, thus maintaining a charge charges go to earth, thus maintaining a charge balance in the areas of the conductor that are not balance in the areas of the conductor that are not affected by the electric field.affected by the electric field.

Walking on carpet

Thoughts and theories

Walking across carpet

Walking across a carpet creates a charge imbalance on the lower surface of shoes.

A strong electric field

This charge imbalance creates a strong electric field that emanates in all directions.

The material in the sole of shoe enables a strong field to influence charges within foot.

An induced charge

Since the body is relatively conductive, the charges that are repelled from the lower regions of my foot set up a charge throughout the rest of my body.

But the body still has a balanced charge overall (it has not lost or gained any charges).

Contacting a source of charges While you are still

on the carpet (still influenced by the electric field on the sole of your shoe),you briefly touch a metallic object (a chair, table, door knob, metal stapler, etc.)

This enables charges to be provided by the metallic object.

Charging through the air

This movement of charges is thus producing an overall charge imbalance in my body, since I was previously neutral overall.

If the charge imbalance on my body is large enough, I do If the charge imbalance on my body is large enough, I do not need to touch the object, as the imbalance could allow not need to touch the object, as the imbalance could allow a movement of charges through the air.a movement of charges through the air.

An overall charge imbalance

Therefore, after that brief encounter with the metallic object, my body now has an overall charge imbalance.

Removing that charge

The only way to remove the possibility of damaging an ESD-sensitive device or assembly is to remove the overall charge imbalance on my body.

This is done by connecting my body to the ready source of charges that is at the same reference potential as the item I wish to handle - using a wrist strap or foot strap.

ELECTROSTATIC DISCHARGE PROCESSELECTROSTATIC DISCHARGE PROCESS

1. Charge is generated on the surface of an insulator.

2. This charge is transfered to a conductor by contact or induction.

3. The charged conductor comes near a metal object (grounded or ungrounded) and a discharge occurs.

4. When a discharge occurs to an ungrounded object, the discharge current flows through the capacitance between the object and ground.

STATIC GENERATIONSTATIC GENERATION

THE STATIC CHARGE IS GENERATED BY IMBALANCE

IN THE MOLECULAR STRUCTURE BY RUBBING;

CAUSING STRIPPING OF NEGATIVELYCHARGED

ELECTRONS WITH ONE MATERIAL GETTING PASITIVE

CHARGE AND OTHER NEGATIVE

CAUSE FOR STATIC CHARGECAUSE FOR STATIC CHARGE

FRICTION

SEPERATION

INDUCTION

CAUSES FOR ESD GENERATIONCAUSES FOR ESD GENERATION

WALKING ON SYNTHETIC SURFACE

RELATIVE MOVEMENT ON CHAIR

TABLE, COMPUTER, PLASTIC PARTS NYLON OR

SYNTHETIC CLOTHES

CLEANING WITH COMPRESSED AIR

CLEANING WITH SOLVENT

ESDESD

FACTORS:FACTORS:

TYPE OF MATERIAL

RELATIVE HUMIDITY

TYPE OF CLOTHING

SPEED AND MANNER OF WALKING

BODY RESISTANCE

RECORDED ESD ACCIDENTSRECORDED ESD ACCIDENTS

In 1937, The German flying boat Hinderburg arriving in Lakehurst, New Jersey, caught fire while anchoring at its landing mast.

In 1970’s, in USA, a space craft launching rocket exploded during the fueling operation, killing 3 engineers.

In January, 1985, during the assembly of a missile in Germany, the motor case made of Kelvar, got rubbbed against the cushioning in its container. The ESD generated caused the highly flammable propellant to catch fire and the motor exploded, killing 3 people.

3 to 30% of Integrated Circuits manufactured every year die in “infancy” due to ESD.

Device sensitivity to Electrostatic Discharge

At higher magnification the pit in the area between the base and emitter becomes more obvious

Device sensitivity to Electrostatic Discharge

At this magnification see the 1/2 of

the width of the material has been destroyed.

40 – 50% EQUIPMENTS HAVE 40 – 50% EQUIPMENTS HAVE

FAILED IN THE FIELD FAILED IN THE FIELD

DUE TO ESDDUE TO ESD

Statistics

SENSITIVE CONSTITUENTS FAILURE MODES

MOS STRUCTURES SHORT

BIPOLAR JUNCTIONS LEAKAGE

FILM RESISTORS VALUE SHIFT

METALIZATION STRIPES OPEN

FIELD PERFECT STRUCTURES OPERATIONAL

PIEZOELECTRIC CRYSTALS DEGRADED

CLOSELY SPACED CONDUCTORS DEGRADED

• PLASTICS

• CONDUCTORS

• FURNITURES

• VINYL FLOOR

• COOLING FANS WITH PLASTIC BLADES

• PRINTERS/COPIERS

• PAPER

• NYLON & WOOLLEN GARMENTS

• COMPRESSED AIR GUN

ESD SOURCESESD SOURCES

MAN MADE:MAN MADE:

NATURAL:NATURAL:

• HUMAN BODY

• MOVEMENT OF CLOUDS

PACKING HANDLING MATERIALS:

COMMON POLYTHENE BAGS, WRAPS,ENVELOPES

COMMON BUBBLE PACK FOAM

COMMON PLASTIC TRAYS, PLASTIC TOTE BOXES, VIALS

TYPICAL CHARGE GENERATORSTYPICAL CHARGE GENERATORS

ASSEMBLY, CLEANING, TEST & REPAIR AREA ITEMS:

SPRAY CLEANERS

COMMON SOLDER SUCKERS

COMMON SOLDER IRONS

SOLVENT BRUSHING ( SYNTHETIC BRISTLES)

CLEANING, DRYING

TEPARATURE CHAMBERS

ESD VOLTAGE MEASUREMENTELECTROSTATIC VOLTAGE

MEANS OF STATIC GENERATION 10% RW 40% RW 55% RW

PERSON WALKING ACROSS CARPET

PERSON WALKING ACROSS VINYLFLOOR

WORKER AT A BENCH

CERAMIC DIPS IN PLASTIC TUBE

CERAMIC DIPS IN VINYL SET UP TRAYS

CIRCUIT AS BUBBLE PLASTIC COVER REMOVED

CIRCUIT AS PACKED IN FOAM LINED SHIPPING BOX

35000 15000 7500

12000 5000 3000

6000 800 400

2000 700 400

11500 4000 2000

25000 20000 7000

21000 11000 5500

REASONS FOR DISBELIEF

ESD DAMAGE : WHEN UNNOTICED?

HUMAN SENSE OF FEELING OF STATIC AT 4000V MUCH MORE HIGHER THAN SENSITIVITY OF COMPONENTS

HARDLY ANY PHYSICAL DAMAGE

ESD FAILURES CONSIDERED AS GENERAL COMPONENT FAILURE

FAILURE MAY NOT BE INSTANT. (LATENT FAILURE)

GUIDE TO STATIC CONTROL MATERIALSGUIDE TO STATIC CONTROL MATERIALS

SURFACE RESISTIVITY-OHMS PER SQUARE

INSULATOR

MATERIALS IN THIS RANGE ARE NOT EFFECTIVE FOR STATIC CONTROL1012 To 10 15

1010 To 10 12

ANTISTATIC

THESE MATERIALS DO NOT GENERATE AND SUPPORT HIGH STATIC CHARGES. BUT DISCHARGE RATES ARE TOO SLOW FOR MOST INDUSTRIAL APPLICATIONS.





STATIC DISSIPATORS ( PARTIALLY CONDUCTIVE)

MATERIALS MOST SUITABLE FOR STATIC CONTROL WORK SURFACES, FLOORING AND FLOOR MATS, SEALING, OVERALLS

106 To 10 9


SURFACE RESISTIVITY-OHMS PER SQUARECONDUCTIVE

MATERIALS FOR CONTAINERS AND HANDLING EQUIPMENT.BELOW 104 OHMS PER SQUARE EFFECTIVE STATIC SHIELDING IS POSSIBLE,OPERATOR SAFELY WILL BE COMPROMISED IF THE EARTH PATH THROUGH BENCH MATS, FLOOR MATS AND FLOORING LESS THAN 5 X 104 OHMS AND MAINS POWERED EQUIPMENT’S IN USE.

101 To 10 4

OBJECTIVES OF ESD CONTROLOBJECTIVES OF ESD CONTROL

PREVENTING STATIC CHARGE GENERATION

DISSIPATING THE DEVELOPED CHARGE

NEUTRALISING DEVELOPED CHARGE FOR A CHARGE

FREE ZONE

CONTROLLING OF ESDCONTROLLING OF ESDWORK SURFACE

AIR

HUMAN BODY

FLOOR

DO’SDO’S MINIMISE HANDLING.

KEEP PARTS IN ORIGINAL PACKING UNTILL READY FOR USE.

USE ESD PROTECTIVE CONTAINERS AND BAGS.

DISCHARGE STATIC BEFORE HANDLING DEVICE BY TOUCHING NEARBY GROUNDED SURFACE.

HANDLE DEVICES BY THE BODY.

TOUCH THE ESD PROTECTIVE PACKAGE BEFORE TOUCHING INSIDE OF DEVICE.

KEEP A DUST FREE WORK AREA.

DONT’SDONT’S TOUCH THE LEADS OF DEVICE.

SLIDE ES DEVICES OVER ANY SURFACE.

PUT MASKING TAPE ON PROGRAMMABLE IC’S.

STORE OR CARRY SENSITIVE COMPONENTS OR ASSEMBLIES IN PLASTIC BAGS.

STORE SENSITIVE COMPONENTS IN THERMOCOLE/PLASTIC FOAM.

HANDLE ES DEVICES IN “NON ESD CONTROLLED” ENVIRONMENT.

ESD MODELS

ESD MODELS HAVE BEEN DEFINED TO DESCRIBE THE EFFECTS ON ESD SENSITIVE DEVICES:

HUMAN BODY MODEL

CHARGED DEVICE MODEL

MACHINE MODEL

Human Body Model (HBM)Human Body Model (HBM)

The basic human body model consists of body capacitance and resistance. The charge is stored in the body capacitance and the discharge occurs through the body resistance.

When a charged person handles or comes in close proximity to an ESD sensitive part, the part may be damaged by direct discharge or by an electro static field.

<0.1mH Rb

Vb Cb

Cb : 50 to 350pFRb : 150 to 10KOhmsVb : 3 to 20 KV

^

Human Body Model (HBM)

HUMAN BODY CAPACITANCE AND RESISTANCEHUMAN BODY CAPACITANCE AND RESISTANCE

o

50-100pF 50pF

100pF100pF

Rb

o

^

^

TYPICAL ESD CURRENT WAVE FORMTYPICAL ESD CURRENT WAVE FORM

. . . . . . . .

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

ttf=100nSectr=1nSec

40A

I^

^

Machine Model

A discharge similar to the HBM event also can occur from a charged conductive object, such as a metallic tool or fixture.

.

Charged Device ModelThe transfer of charge from an ESDS device is also an ESD event. A device may become charged, for example, from sliding down the feeder in an automated assembler. If it then contacts the insertion head or another conductive surface, a rapid discharge may occur from the device to the metal object. This event is known as the Charged Device Model (CDM).

ESD CONTROL DEVICESESD CONTROL DEVICES

ANTISTATIC VINYL TABLE MAT

CONDUCTIVE FLOOR MAT

ESD LAMINATE

ESD WRIST STRAP

ESD HEEL STRAP

ESD TOE STRAP

COMMON POINT GROUND

ANTISTATIC BINS/TRAYS

PCB STORAGE RACK

CONDUCTIVE FOAM

Typical Facility AreasRequiring ESD Protection

ReceivingInspectionStores and warehousesAssemblyTest and inspectionResearch and developmentPackagingField service repairOffices and laboratoriesClean rooms

ESD AUDITESD AUDIT

MATERIALS CLASSIFICATIONMATERIALS CLASSIFICATION

MATERIAL SURFACE VOLUME

CLASS RESISTIVITY RESISTIVITY

SHIELDING 104 OR LESS 102 OR LESS

CONDUCTIVE 105 OR LESS 104 OR LESS

DISSIPATIVE 105 TO 1010 104 TO 109

ANTISTATIC 1010 TO 1012 ---

INSULATIVE >1015 >1014

ESD AUDITESD AUDIT

PERSONNEL TRAINING FOR ESD PREVENTIVE

AWARENESS TRAINING

CERTIFICATION TRAINING

CONTROL PROGRAM AUDIT

ESD TEST & MEASURING INSTRUMENTSESD TEST & MEASURING INSTRUMENTS

STATIC CHARGE METER

WRIST STRAP AND GROUND TESTER

FOOTWEAR TESTER

SURFACE RESISTIVITY METER

STATIC SENSOR

CONTINUOUS WRIST STRAP MONITOR

CONTINUOUS WORK STATION MONITOR

TEMPARATURE AND HUMIDITY INDICATOR

TESTING EVALUATIONTESTING EVALUATION

The test evaluation report consists of the following test areas for each ESD item/s:POINT TO POINT SURFACE RESISTIVITY TOP/BOTTOM

POINT TO POINT SURFACE RESISTIVITY IN/OUT

SURFACE TO GROUND RESISTANCE

PERSON TO GROUND RESISTANCE

STATIC CHARGE MEASURING TEST

STATIC SHIELDING TEST

TESTING EVALUATIONTESTING EVALUATION

Antistatic P.E Bags

Static Shield Bags

Conductive Bags

Conductive Grid Bags

Antistatic Aprons

Conductive Brush

Foot Wear

ESD Mat

conductive Mat

Work Surface

ESD Laminate

Wrist Strap

Heel Strap

ESD Chair

The tests are generally conducted for the following item/s:

PERSONAL GROUNDING

Two types of Personal Grounding:

Wrist Straps

Footwear

WRIST STRAPS

Daily Check with Wrist Strap Worn

Test with a Wrist Strap tester

Floor

Point to Point

Floor

Resistance to Ground

Garments

Point to Point

Garments Point to Ground

May need person wearing garment

Needs to be connected to ground as wor n

Chair

Check all parts of Chairs to Ground

Seat, Backrest, Armrest, Foot Rest

TYPES OF ESD DAMAGE

CATASTROPHIC FAILURE

UPSET FAILURE

SHIELDING

FARADAY CAGETypes of Faraday Cages

• Metallized & Conductive Shielding Bags

• Conductive tote box with cover

A hollow conductor

A Faraday Cage is a hollow conductor.

Michael Faraday

WORK STATION

Electrostatic Voltmeter (ESV)

Measurement of Static Electricity

Static electricity is measured in coulombs. The charge "q" on

an object is determined by the product of the capacitance of

the object "C" and the voltage potential on the object (V):

q=CV

Commonly, however, we speak of the electrostatic potential

on an object, which is expressed as voltage.

ESD Damage-How Devices Fail

Electrostatic damage to electronic devices can occur at any

point from manufacture to field service.

Damage results from handling the devices in uncontrolled

surroundings or when poor ESD control practices are used.

Generally damage is classified as either a catastrophic

failure or a latent defect.

electro static discharge awareness and control an extensive course on

Documents

contact slide

electron lost slide

ic chips slide

charge imbalance

lightning zapping slide

stronger force slide

negative charges

triboelectric charge