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An extensive course on. ELECTRO STATIC DISCHARGE AWARENESS AND CONTROL. Examples : Lightning Zapping. An atom is made up of charges. An atom is made up of charges.

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Presentation Transcript
slide1

An extensive course on

ELECTRO STATIC DISCHARGE

AWARENESS AND CONTROL

slide2

Examples :

Lightning

Zapping

an atom is made up of charges
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

Electron “lost”

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

This powerful, rapid movement of charges can damage electronic components.

  • This movement of charges is called a discharge.

Let’s see it again!

slide6

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 EVENT

IT IS AN UNPLANNED OCCURANCE OF ELECTRO- STATIC DISCHARGE

slide7

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

the most common causes of esd are
The most common causes of ESD are:

Moving people

Improper grounding

Unshielded cables

Poor connections

Moving machines

Low humidity (hot and dry conditions)

slide11
To avoid damaging static-sensitive devices, the following procedures will help to minimize the chances of destructive static discharges:

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.

triboelectric generation

Triboelectric generation

Basic Principles (2)

when materials are in contact
When materials are in contact

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

when materials are in contact1
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 two materials are in intimate contact, they share electrons which are at their surfaces.

when the materials are separated

Electrons “lost”

Electrons “gained”

When the materials are separated

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

when the materials are separated1

Electrons “lost”

Electrons “gained”

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

when the materials are separated2

Electrons “lost”

Electrons “gained”

When the materials are 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.

The loss and gain of these electrons creates an imbalance of negative and positive charges on the surface of each material.

when the materials are separated3

Electrons “lost”

Electrons “gained”

When the materials are separated

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

when the materials are separated4

Electrons “lost”

Electrons “gained”

When the materials are separated

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

when the materials are separated5

Electrons “lost”

Electrons “gained”

When the materials are separated

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

charging by induction

Charging by Induction

Basic Principles

charging by induction1
Charging by induction

The charge imbalance on a surface produces an electric field.

The presence of this very strong force causes similar charges on the surfaces of nearby conductors to be repelled.

charging by induction2
Charging by induction

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

walking on carpet

Walking on carpet

Thoughts and theories

walking across carpet
Walking across carpet
  • Walking across a carpet creates a charge imbalance on the lower surface of shoes.
a strong electric field
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
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
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

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

Charging through the air
  • This movement of charges is thus producing an overall charge imbalance in my body, since I was previously neutral overall.
an overall charge imbalance
An overall charge imbalance
  • Therefore, after that brief encounter with the metallic object, my body now has an overall charge imbalance.
removing that charge
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.
slide37

ELECTROSTATIC 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.

slide38

STATIC 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 CHARGE

  • FRICTION
  • SEPERATION
  • INDUCTION
slide39

CAUSES FOR ESD GENERATION

ESD

  • WALKING ON SYNTHETIC SURFACE
  • RELATIVE MOVEMENT ON CHAIR
  • TABLE, COMPUTER, PLASTIC PARTS NYLON OR SYNTHETIC CLOTHES
  • CLEANING WITH COMPRESSED AIR
  • CLEANING WITH SOLVENT
slide40

FACTORS:

      • TYPE OF MATERIAL
      • RELATIVE HUMIDITY
      • TYPE OF CLOTHING
      • SPEED AND MANNER OF WALKING
      • BODY RESISTANCE
slide41

RECORDED 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.
slide42

Device sensitivity to Electrostatic Discharge

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

slide43

Device sensitivity to Electrostatic Discharge

At this magnification see the 1/2 of

the width of the material has been destroyed.

slide46

Statistics

40 – 50% EQUIPMENTS HAVE FAILED IN THE FIELD

DUE TO ESD

slide47

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

slide48

ESD SOURCES

MAN MADE:

  • PLASTICS
  • CONDUCTORS
  • FURNITURES
  • VINYL FLOOR
  • COOLING FANS WITH PLASTIC BLADES
  • PRINTERS/COPIERS
  • PAPER
  • NYLON & WOOLLEN GARMENTS
  • COMPRESSED AIR GUN
slide49

NATURAL:

          • HUMAN BODY
  • MOVEMENT OF CLOUDS
slide50

TYPICAL CHARGE GENERATORS

  • PACKING HANDLING MATERIALS:
    • COMMON POLYTHENE BAGS, WRAPS,ENVELOPES
    • COMMON BUBBLE PACK FOAM
    • COMMON PLASTIC TRAYS, PLASTIC TOTE BOXES, VIALS
  • ASSEMBLY, CLEANING, TEST & REPAIR AREA ITEMS:
    • SPRAY CLEANERS
    • COMMON SOLDER SUCKERS
    • COMMON SOLDER IRONS
    • SOLVENT BRUSHING ( SYNTHETIC BRISTLES)
    • CLEANING, DRYING
    • TEPARATURE CHAMBERS
slide51

ESD VOLTAGE MEASUREMENT

ELECTROSTATIC VOLTAGE

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

PERSON WALKING ACROSS CARPET

35000 15000 7500

12000 5000 3000

PERSON WALKING ACROSS VINYL

FLOOR

6000 800 400

WORKER AT A BENCH

2000 700 400

CERAMIC DIPS IN PLASTIC TUBE

11500 4000 2000

CERAMIC DIPS IN VINYL SET UP TRAYS

CIRCUIT AS BUBBLE PLASTIC

COVER REMOVED

25000 20000 7000

CIRCUIT AS PACKED IN FOAM

LINED SHIPPING BOX

21000 11000 5500

slide52

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)
slide53

GUIDE TO STATIC CONTROL MATERIALS

SURFACE RESISTIVITY-OHMS PER SQUARE

INSULATOR

MATERIALS IN THIS RANGE ARE NOT EFFECTIVE FOR STATIC CONTROL

1012 To 10 15

slide54

GUIDE TO STATIC CONTROL MATERIALS

SURFACE RESISTIVITY-OHMS PER SQUARE

ANTISTATIC

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

1010 To 10 12

slide55

GUIDE TO STATIC CONTROL MATERIALS

SURFACE RESISTIVITY-OHMS PER SQUARE

STATIC DISSIPATORS ( PARTIALLY CONDUCTIVE)

106 To 10 9

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

slide56

GUIDE TO STATIC CONTROL MATERIALS

SURFACE RESISTIVITY-OHMS PER SQUARE

CONDUCTIVE

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

slide57

OBJECTIVES OF ESD CONTROL

  • PREVENTING STATIC CHARGE GENERATION
  • DISSIPATING THE DEVELOPED CHARGE
  • NEUTRALISING DEVELOPED CHARGE FOR A CHARGE
  • FREE ZONE

CONTROLLING OF ESD

  • WORK SURFACE
  • AIR
  • HUMAN BODY
  • FLOOR
slide58

DO’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.
slide59

DONT’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.
slide60

ESD MODELS

  • ESD MODELS HAVE BEEN DEFINED TO DESCRIBE THE EFFECTS ON ESD SENSITIVE DEVICES:
          • HUMAN BODY MODEL
          • CHARGED DEVICE MODEL
          • MACHINE MODEL
slide61

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

Cb : 50 to 350pF

Rb : 150 to 10KOhms

Vb : 3 to 20 KV

Vb

Cb

slide63

HUMAN BODY CAPACITANCE AND RESISTANCE

Rb

^

o

o

^

50-100pF

50pF

100pF

100pF

slide64

TYPICAL ESD CURRENT WAVE FORM

^

I

. . . . . . . .

40A

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

^

tr=1nSec

tf=100nSec

t

slide65

Machine Model

  • A discharge similar to the HBM event also can occur from a charged conductive object, such as a metallic tool or fixture.
  • .
slide66

Charged Device Model

  • The 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).
slide67

ESD 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
slide70

MATERIALS 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

slide71

ESD AUDIT

  • PERSONNEL TRAINING FOR ESD PREVENTIVE
  • AWARENESS TRAINING
  • CERTIFICATION TRAINING
  • CONTROL PROGRAM AUDIT
slide73

ESD 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
slide74

TESTING EVALUATION

The test evaluation report consists of the following test areas for each ESD item/s:

  • POINTTO 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
slide75

TESTING EVALUATION

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

  • 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
slide76

PERSONAL GROUNDING

Two types of Personal Grounding:

Wrist Straps

Footwear

slide77

WRIST STRAPS

  • Daily Check with Wrist Strap Worn
  • Test with a Wrist Strap tester
slide78

Floor

  • Point to Point
slide79

Floor

  • Resistance to Ground
slide80

Garments

  • Point to Point
slide81

Garments

  • Point to Ground
  • May need person wearing garment

Needs to be connected to ground as wor n

slide82

Chair

  • Check all parts of Chairs to Ground
  • Seat, Backrest, Armrest, Foot Rest
slide85

TYPES OF ESD DAMAGE

CATASTROPHIC FAILURE

  • UPSET FAILURE
slide86

SHIELDING

  • Types of Faraday Cages
    • Metallized & Conductive Shielding Bags
    • Conductive tote box with cover

FARADAY CAGE

a hollow conductor
A hollow conductor
  • A Faraday Cage is a hollow conductor.

Michael Faraday

slide90

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.
slide91

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.