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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.
                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”
                            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
                                  When something which has
 This powerful, rapid              a charge imbalance is
movement of charges                brought close to or touches
can damage electronic              something else, a stream of
     components.                   charges might move, to try
                                   to bring the atoms back to
                                   their stable balanced
                                   condition.

                Let’s see it            This movement of
                  again!                 charges is called a
                                         discharge.
             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
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:
   Moving people
   Improper grounding
   Unshielded cables
   Poor connections
   Moving machines
   Low humidity (hot and dry conditions)
Figure 13-14: Power Transmission System
Figure 13-15: Grounds on IC Chips
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


        Basic Principles (2)
  When materials are in contact




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




 It is possible for electrons to be “stolen” from one
When two materials are in intimate contact, they share
material by nuclei in the other material, because they
        electrons which are at their surfaces.
                 have a stronger force
  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.
   When the materials are
   separated Electrons “lost”



                    Electrons “gained”


   When these materials are separated, electrons With
This action takes place with all types of materials.are
 removed from one material and the points of contact.
 insulators, the charges remain atare transferred to the
  A charge spreads all over an ungrounded conductor.
                     other material.
The triboelectric
charge when two
materials placed in
contact are then
separated.
When the materials are separated
                         Electrons “lost”




                       Electrons “gained”

    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 separated
                     Electrons “lost”




                    Electrons “gained”


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

                      Electrons “lost”




                     Electrons “gained”



 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 separated

                   Electrons “lost”




                  Electrons “gained”

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 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 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.
Charging by induction
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
   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.

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

 WALKING ON SYNTHETIC SURFACE
                                 ESD
 RELATIVE MOVEMENT ON CHAIR
 TABLE, COMPUTER, PLASTIC PARTS NYLON OR
                     SYNTHETIC CLOTHES
 CLEANING WITH COMPRESSED AIR
 CLEANING WITH SOLVENT
FACTORS:
    TYPE OF MATERIAL
    RELATIVE HUMIDITY

    TYPE OF CLOTHING

    SPEED AND MANNER OF WALKING

    BODY RESISTANCE
              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.
         Device sensitivity to Electrostatic Discharge

At higher
magnificat
ion the pit
in the area
between
the base
and
emitter
becomes
more
obvious
        Device sensitivity to Electrostatic Discharge
At this
magnific
ation see
the 1/2 of
the width
of the
material
has been
destroyed
.
       Statistics
40 – 50% EQUIPMENTS HAVE
  FAILED IN THE FIELD
      DUE TO ESD
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
            ESD SOURCES
MAN MADE:
            • PLASTICS
            • CONDUCTORS
            • FURNITURES
            • VINYL FLOOR
            • COOLING FANS WITH PLASTIC BLADES
            • PRINTERS/COPIERS
            • PAPER
            • NYLON & WOOLLEN GARMENTS
            • COMPRESSED AIR GUN
NATURAL:

       • HUMAN BODY

  • MOVEMENT OF CLOUDS
    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
              ESD VOLTAGE MEASUREMENT
                                     ELECTROSTATIC VOLTAGE

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

PERSON WALKING ACROSS CARPET         35000      15000        7500

PERSON WALKING ACROSS VINYL          12000       5000        3000
FLOOR
WORKER AT A BENCH                     6000         800        400

CERAMIC DIPS IN PLASTIC TUBE          2000        700         400

CERAMIC DIPS IN VINYL SET UP TRAYS   11500        4000       2000

CIRCUIT AS BUBBLE PLASTIC            25000       20000       7000
               COVER REMOVED
CIRCUIT AS PACKED IN FOAM            21000       11000       5500
            LINED SHIPPING BOX
              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 MATERIALS
        SURFACE RESISTIVITY-OHMS PER SQUARE

                    INSULATOR


                    MATERIALS IN THIS RANGE ARE NOT
1012   To   10 15   EFFECTIVE FOR STATIC CONTROL
     GUIDE TO STATIC CONTROL MATERIALS

          SURFACE RESISTIVITY-OHMS PER SQUARE
                    ANTISTATIC


                     THESE MATERIALS DO NOT GENERATE
1010 To   10 12      AND SUPPORT HIGH STATIC CHARGES.
                     BUT DISCHARGE RATES ARE TOO SLOW
                     FOR MOST INDUSTRIAL APPLICATIONS.
    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
          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
101 To     4 POSSIBLE,OPERATOR     SAFELY    WILL
         10 COMPROMISED IF THE EARTH PATH THROUGH
                                                    BE

             BENCH MATS, FLOOR MATS AND FLOORING LESS
             THAN 5 X 104 OHMS AND MAINS       POWERED
             EQUIPMENT’S IN USE.
        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
                 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.
                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.
           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)

 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
          Vb                             Rb : 150 to 10KOhms
                Cb                       Vb : 3 to 20 KV
Human Body Model (HBM)
HUMAN BODY CAPACITANCE AND RESISTANCE




                              Rb
                              oo


      50-100pF        50pF



          100pF       100pF
        TYPICAL ESD CURRENT WAVE FORM


 I


40A . . . . . . . ..
                   .
                   .
                   .
                   .
                   .
                   .
                   .
                   .
                   .
                   .
                   .
                   .
                   .
                   .
                   .
                   .
                   .
                   .
                   .
         tr=1nSec      tf=100nSec   t
         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 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).
         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
Typical Facility Areas
Requiring ESD Protection

Receiving
Inspection
Stores and warehouses
Assembly
Test and inspection
Research and development
Packaging
Field service repair
Offices and laboratories
Clean rooms
ESD AUDIT
          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
            ESD AUDIT
 PERSONNEL TRAINING FOR ESD PREVENTIVE


 AWARENESS TRAINING


 CERTIFICATION TRAINING


 CONTROL PROGRAM AUDIT
     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
             TESTING 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 EVALUATION
The tests are generally conducted for the following item/s:
                                   

    Antistatic P.E Bags            ESD Mat

    Static Shield Bags             conductive Mat

    Conductive Bags                 Work Surface

    Conductive Grid Bags            ESD Laminate

    Antistatic Aprons               Wrist Strap

    Conductive Brush                Heel Strap

    Foot Wear                       ESD Chair
         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
                 Types of Faraday Cages
FARADAY CAGE
                   • 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.

				
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