ESD AWARENESS AND CONTROL

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An extensive course on
ELECTRO STATIC DISCHARGE AWARENESS AND CONTROL
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Examples Lightning Zapping
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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.

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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.

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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.

Lets see it again!
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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
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What is ESDElectrostatic 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.
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The most common causes of ESD are
Moving people Improper grounding Unshielded
cables Poor connections Moving machines Low
humidity (hot and dry conditions)
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Figure 13-14 Power Transmission System
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Figure 13-15 Grounds on IC Chips
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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.
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Triboelectric generation

• Basic Principles (2)

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When materials are in contact
When two materials are in intimate contact, they
share electrons which are at their surfaces.
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The triboelectric charge of two materials in
contact.
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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.
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When the materials are separated
When these materials are separated, electrons are
removed from one material and are transferred to
the other material.
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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.
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The triboelectric charge when two materials
placed in contact are then separated.
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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.
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When the materials are separated
When the surfaces are rough, this intimacy and
separation is assisted by rubbing the materials
together.
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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
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When the materials are separated
The drier the air (lower relative humidity, RH)
the higher the generated charge
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The creation of a charge when materials are
separated is termed triboelectric charging
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Charging by Induction

• Basic Principles

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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.
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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.
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Charging by induction
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Walking on carpet

• Thoughts and theories

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Walking across carpet

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

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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.

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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).

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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.

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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.

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An overall charge imbalance

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

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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.

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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.
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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

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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

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

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RECORDED ESD ACCIDENTS

• In 1937, The German flying boat Hinderburg
  arriving in Lakehurst, New Jersey, caught fire
  while anchoring at its landing mast.
• In 1970s, 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.

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Device sensitivity to Electrostatic Discharge
At higher magnification the pit in the area
between the base and emitter becomes more obvious
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Device sensitivity to Electrostatic Discharge
At this magnification see the 1/2 of the width of
the material has been destroyed.
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Statistics
40 50 EQUIPMENTS HAVE FAILED IN THE FIELD DUE
TO ESD
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SENSITIVE CONSTITUENTS FAILURE MODES
MOS STRUCTURES SHORT BIPOLAR JUNCTIONS LEAKAGE
FILM RESISTORS VALUE SHIFT METALIZATION
STRIPES OPEN FIELD PERFECT STRUCTURES OPERATION
AL PIEZOELECTRIC CRYSTALS DEGRADED CLOSELY
SPACED CONDUCTORS DEGRADED
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ESD SOURCES
MAN MADE

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

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NATURAL

• HUMAN BODY
• MOVEMENT OF CLOUDS

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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

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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
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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)

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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
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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
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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
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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 EQUIPMENTS IN USE.
101 To 10 4
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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

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• DOS
• 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.

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DONTS

• TOUCH THE LEADS OF DEVICE.
• SLIDE ES DEVICES OVER ANY SURFACE.
• PUT MASKING TAPE ON PROGRAMMABLE ICS.
• 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.

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ESD MODELS

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

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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.

lt0.1mH
Rb
Cb 50 to 350pF Rb 150 to 10KOhms Vb 3 to 20
KV
Vb
Cb
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Human Body Model (HBM)
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HUMAN BODY CAPACITANCE AND RESISTANCE
Rb

o
o

50-100pF
50pF
100pF
100pF
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TYPICAL ESD CURRENT WAVE FORM

I
. . . . . . . .
40A
. . . . . . . . . . . . . . . . . . . .

t
tf100nSec
tr1nSec
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Machine Model A discharge similar to the HBM
event also can occur from a charged conductive
object, such as a metallic tool or fixture. .
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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).
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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

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ESD AUDIT
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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
gt1015 gt1014
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ESD AUDIT

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

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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

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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

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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

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PERSONAL GROUNDING
Two types of Personal Grounding
Wrist Straps Footwear
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WRIST STRAPS

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

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Floor

• Point to Point

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Floor

• Resistance to Ground

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Garments

• Point to Point

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Garments

• Point to Ground
• May need person wearing garment

Needs to be connected to ground as wor n
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Chair

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

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TYPES OF ESD DAMAGE
CATASTROPHIC FAILURE

• UPSET FAILURE

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SHIELDING

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

FARADAY CAGE
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A hollow conductor

• A Faraday Cage is a hollow conductor.

Michael Faraday
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WORK STATION
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Electrostatic Voltmeter (ESV)
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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) qCV Commonly,
however, we speak of the electrostatic potential
on an object, which is expressed as voltage.
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• 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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