ELECTROSTATIC DISCHARGE (ESD)
AWARENESS TRAINING
Credits
Prepared by
CAPT JESSE D. S. MORGAN, III
Additional Slides by
JULIUS BRODBECK
Technical Assistance by
Steve Gerken and Mike Manders
AF ESD Control Center
Materials Integrity Branch
Materials and Manufacturing Directorate
Air Force Research Laboratories
AFMC
1
What is ESD?
Electrostatic Discharge (ESD) is the discharge
of stored static electricity.
• Some circuits today are sensitive to as little
as 25 volts. Typically humans begin to feel
a static discharge at 3500 volts.
• You can damage a circuit without feeling it!
2
Overview
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Extent of ESD Damage
Directives
Definitions
Summary of ESD Principles
Tribocharging
Effects of Humidity
Controlling Body Voltage
Packaging
Marking, Labeling, and signs
ESD Worksurfaces
Air Ionization
Grounding
The Role of Capacitance
Reference
4
ESD Damage, 1st of
Extent of ESD Damage
7
Photo taken on a Microscope of ESD damage
Micro Wire
5
A DEMO on a MOSFET
A 3N157 MOSFET is lying on a circuit board to
illustrate the relative size of the all metal package.
6
An ESD Shock is applied
7
Microscopic Postmortem
There is no visible damage at 150 power !
8
2500 Magnification
At 2500 power, damage to a via is seen.
9
Extent of ESD Damage
Susceptibility
Susceptibility of Various Devices Exposed to ESD
Device Type
Range of ESD
Susceptibility (Volts)
MOSFET
100 - 200
JFET
140 - 1,000
CMOS
250 - 2,000
Schottky Diodes, TTL
300 - 2,500
Bipolar Transistors
300 - 7,000
SCR
600 - 1,000
“Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.39
10
Extent of ESD Damage
Telephone Systems
Estimate of Telephone System ESD Costs
150
160
129
140
120
100
160
94
80
60
40
20
0
25
78
35
4
3
4
3
79 Year 80
81
= Range of ESD Damage
“Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.17
11
Extent of ESD Damage
Published ESD Losses
1980 Delco Electronics study on Auto
Electronics Product ESD Failures
$22M
1983 AT&T HIC Shop ESD Losses
39%
1984 USAF Missile Guidance Video Board
ESD Failures (250 Failed)
$492,000
1984 USAF Depot ESD failures
$788,000
1985 Early IBM Printer Module ESD Failures
62%
“Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.19
12
Extent of ESD Damage
Air Force’s ESD Estimate
Estimate of Failures Due to ESD
1988 USAF, A Review of EOS/ESD Field Failures
in Military Equipment.
Up to 12 %
of the
Failures
could be
ESD.
17%
25%
6%
IC Design
Fabrication and
Assembly
Electrical
Overstress
(EOS)
Electrostatic
Discharge (ESD)
6%
EOS or ESD
Capt Thomas Green
1988 EOS / ESD
Symposium
Proceedings
Retest OK
46%
13
Extent of ESD Damage
Damage in Manufacturing
EOS/ESD Damage During Manufacturing.
• Data from 23 designs from High Reliability Facility.
– Out of 1193 Processing Failures.
 There were 414 EOS/ESD Failures.
• At Another Plant 1607 Devices Were Analyzed.
– The Conclusion in 1993 was.
“25.8 % of the product rejected by this.
facility was damaged by the cumulative.
effects of EOS and ESD, all of which.
were avoidable.”
“Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.20
14
Extent of ESD Damage
Repair Cost vs Discovery
REPAIR COSTS
Level where
Fault was
Discovered
Hewlett
Packard
Commercial
Product
Gould
Military
System
Device
$1
$5
Board
$5
$50
System
$50
$1,500
Field
$500
$10,000
“Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.16
15
Directives
Directives, 1st of 6
 Air Force Policy Directive 21-1 and 21-3
“Compliance with AF T.O.s is mandatory”
 T.O. 00-25-234, General Shop Practice
Requirement for the Repair, Maintenance, and
Test of Electrical Equipment.
 ANSI/ESD S20.20, Development of an ESD
Control Program is replacing Mil-Std-1686
 MIL-HDBK-263B, Electrostatic Discharge
 Local Operating Instructions
16
Directives
Authorize Time & Money
The following Air Force documents authorize
AF time and money for ESD Control as indicated
Section 7 of T.O. 00-25-234)?
 AF Policy Directive 21-3
 AF Policy Directive 21-1
 AFI 21-116
 AFI 24-202
17
Directives
Mandatory Compliance
AIR FORCE POLICY DIRECTIVE 21-3, “Technical Orders”
Says… “Compliance with Air Force T.O.s is mandatory”
– Includes TO 00-25-234
AIR FORCE POLICY DIRECTIVE 21-1 “Managing
Aerospace Equipment Maintenance”
Defines Aerospace Equipment as “Equipment used and
maintained to meet the Air Force mission. It includes aircraft,
missiles, space equipment, communications, electronic
equipment, avionics, engines, training equipment, support
equipment, aerospace ground equipment, sound suppresser
systems, test, measurement and diagnostic equipment and
major-end-items of all equipment”
18
Directives
AFI 21-116
AIR FORCE INSTRUCTION 21-116 “Maintenance and
Management of Communication Electronics”
Para 5.17.4.3.7.9, under responsibilities of the Maintenance
Support Representative (MSR) requires:
“Compliance with Electrostatic Discharge practices, where
applicable. (TO 00-25-234)”
TECHNICAL ORDER 00-25-234, “General Shop Practice
Requirements for the Repair, Maintenance, and Test of Electrical
Equipment”
Says… “The provisions contained herein are applicable to Air
Force and contractual personnel engaged in repair, maintenance,
or test of Aerospace Electronic Equipment”
19
Directives
Supply is to Comply
ESD Control in Supply
AIR FORCE INSTRUCTION 24-202 “Preservation and
Packaging” Chapter 2 (Packaging Operations), paragraph 2.4:
Packaging Line Layout should include: “At least one electrostatic
discharge (ESD) protective workstation where trained personnel
can package sensitive (ESDS) items. This must include a
conductive work surface and personnel grounding devices. TO
00-25-234, Section VII, contains detailed information about ESD
protective workstations. Post signs prohibiting entry of
unauthorized personnel and static-producing materials in areas
designated for packaging ESDS items”
20
Directives
Supply & AFI
24-202
AIR FORCE INSTRUCTION 24-202 Chapter 3, “Preserving Supply
and Equipment Items”, para 3.2, “Electrostatic Discharge Sensitive Items” says:
3.2 “Never handle ESD-sensitive items, regardless of
condition, without their protective packaging except at a
grounded ESD workstation.”
3.2.1. Use care in opening ESD items. ESD bags are
usually constructed with enough extra material to allow
for at least one additional heat seal, thereby facilitating
reuse in the maintenance activity.
3.2.2. Identify ESD items by Type Cargo Code 3 on DD
Form 1348-1A, and by special interior and exterior
sensitive-electronic-device caution label .
21
Definitions
Electrical
Definitions
 Conductors
- Materials that permit the free
movement of electrons.
 Electrons
- Small negatively charged particles
 Electric Current
- Movement of free electrons
 Insulators
- Materials that impede the free
movement of electrons.
 Negative Charge - A surplus of electrons
 Positive Charge
- A deficiency of electrons
 A Proton
- A positively charged particle
Ms. Kim Wagner, Hill AFG, OO-ALC / TIUBA
22
Definitions
Classification
Resistance
Classification
Sheet Resistivity
• Conductive
100-105 Ohms/Square
• Static Dissipative
105 to 1012 Ohms/Square
• Insulative
Greater than 1012 Ohms/Square
Section 7 of AF T.O. 00-25-234
• Conductive
100-106 Ohms
• Static Dissipative
106 to 109 Ohms
• Insulative
Not Defined
Ohms / Square is done with special electrodes and converted
to a number that is about 10 X more than is obtained by 7.8 a
Work Surface Test Procedure.
23
ESD Physics
ESD Physics, 1st
of 6
• Tribocharging
– Separation of surfaces
 Tape
 Binder Pages
+
+
+ +
– Rubbing of surfaces together
 Footwear against the floor
 Clothing against anything it touches
– Flow of fluids
 Fuel, oil and water
24
Ben Franklin Painting
Ben Franklin was
surely protected by
the Angels during his
foolish kite stunt, or
should we say shunt?
Ms. Kim Wagner, Hill AFG, OO-ALC / TIUBA
25
ESD Physics
Both Molecules are
Electrically Neutral
At the Molecular Level
Both Molecules are
Electrically Charged
26
ESD Physics
Charge, Attract &
Repel
Opposite Charges Attract
Charges
+
-
+
Like Charges Repel
+
27
ESD Physics
Electric Field Demonstrations
•
Around insulators
 Styrofoam
* Teflon
+
-
• Around human body standing on an insulator
* With wrist strap
* Without wrist strap
• Absent around grounded conductors
28
ESD Physics
Charge Distribution
NONCONDUCTOR
CONDUCTOR
++--++--++++
+++ - ++--- ++
---- ++++--- -
+++++++++++
+++++++++++
+++++++++++
and
Can have Random
Charge Distribution
(Mixed Shown)
Will have Uniform
Charge Distribution
(Positive Shown)
After
grounding
++--++--++++
+++ - ++--- ++
---- ++++--- -
Before
Does not Discharge
Complete Discharge
“Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.27
29
ESD Physics
Retention of Charges
Retention of Charges After Separation
of Surfaces
GROUNDED CONDUCTOR
no charge
GROUNDED CONDUCTOR
no charge
GROUNDED CONDUCTOR
no charge
INSULATOR
charged
INSULATED CONDUCTOR
charged
INSULATOR
charged
INSULATOR
charged
INSULATOR
charged
“Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.28
30
Tribocharging
Tribocharging
Triboelectric Series
+
Glass
Human Hair
Nylon
Nickel, Copper
Brass, Silver
Gold, Platinum
Polyester
Wool
Celluloid
Lead
Saran
Aluminum
Polyurethane
Paper
Polyethylene
Cotton
Polypropylene
Steel
PVC
Wood
Silicon
Sealing Wax
Teflon
Hard Rubber
“Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.32
31
Tribocharging
Amount & Rate of
Charge
• Amount of Charge Generated
- Relative position in triboelectric series
- Intimacy of contact
- Rate of separation
- Coefficient of friction
• Rate of Discharge
- Conductivity of materials
- Relative humidity
• Moisture on surface
“Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.37
32
Effects of Humidity
Varies with Season Location and and Time
•
Winter, Low Humidity, High Static
– Extra caution is necessary
– The colder it gets, the more electrostatic
discharge
•
Summer, High Humidity, Low Static
•
Desert Areas and at High Atmospheres
– These places have low humidity
– Static is a problem year around
–
–
Exception is Lightening
Difficult to demonstrate static events
33
Effects of Humidity
Voltage &
Humidity
Voltages at Various Humidities
Means of Static Generation
Refer to Table 7-2 in T.O. 00-25-234
Electrostatic Voltages
10%
40%
55%
R.H.
R.H.
R.H.
Person Walking Across Carpet
35,000
15,000
7,500
Person Walking Across Vinyl Floor
12,000
5,000
3,000
Worker at a Bench (No wrist Strap!)
6,000
500
400
120,000
50,000
15,000
60,000
25,000
10,000
White Styrofoam packing
Common plastic bag picked up from bench
Notice that with higher humidity, the charging potentials
decrease significantly but are still at damaging levels.
“Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.38
34
ESD Control Work Areas
• T.O. 00-25-234, Section VII Requires:
• ESD Control Work Area Survey:
The Work Area Survey (performed by the ESD POC)
defines the ESD work area and identifies the
necessary ESD control items required for that work
area.
• Keep Two Basic Rules in Mind:
Handle all ESD Sensitive items at an approved static
control workstation.
Transport and store all static sensitive components,
circuit boards, assemblies and systems in static
shielding (Faraday Cage) packages or containers.
35
ESD Control Work Areas
• T.O. 00-25-234, Section VII Requires:
•ESD Control Work Area Certification:
The Work Area Certification is an evaluation by the
ESD POC to ensure an ESD work area meets the
requirements of the Work Area Survey.
The appropriate certification document (letter signed
by ESD POC) shall be posted at the entrance to the
ESD work area or in a readily accessible file.
36
Controlling Body Voltage
• Wrist Straps
• Purpose:
An ESD control wrist strap is used to prevent body
voltage from damaging ESD sensitive items.
• Use:
Typically, an ESD control wrist strap should be worn
anytime you are handling an ESD sensitive item.
• Testing Requirement:
Single conductor wrist straps shall be tested prior to
first use each day per person.
37
Controlling Body Voltage
• Wrist Straps
• Advantages:
•
•
•
•
•
•
•
Drains body voltage to ground
An economical ESD solution
Can be used almost anywhere
Prevents body voltage buildup
Adjustable size and cord length
Light weight
Ease of use
38
Controlling Body Voltage
Wrist Straps
• Wrist Straps
• Disadvantages:
• You have to remember to use them.
• Requires testing !
• You don’t know when they are working !
• You have to test them periodically
• Reasons for test failures:
• They frequently do not make good
body contact because:
• Body hair, Dry skin, Loose fit
• Worn Cuff, Broken cord, etc.
39
Controlling Body Voltage
Adjustable Cuffs
• Wrist Straps
T.O. 00-25-234 requires that
all wrist straps have adjustable
diameter cuffs.
Metal wrist strap cuffs have
not been approved.
40
Controlling Body
Voltage
Wrist Strap
Warning
WARNING
The personnel wrist strap shall not be
worn when working on energized
parts, assemblies and equipment.
41
Controlling Body
Voltage
Current,
Physiologic
Effects
Effect of Electrical Current on Humans
Current Values (Milliamperes)
AC
Effect
DC
25 TO 400 HZ
0-1
0-4
1-4
4-15
4-21
15-80
21-40
80-160
40-100
160-300
Over 100
Over 300
Perception
Surprise
Reflex Action
Muscular inhibition
Respiratory block
Usually fatal
(Ref. MIL-STD-454) Also in Table 7-4 of TO 00-25-234
42
Controlling Body Voltage
Wrist Strap
Testing
Wrist Strap Testers, Electrical Aspects
Table 7-3 ITEM
61
Passing Range
Ohms
Output
Volts
8x105 to 1x107
8 - 13
Don’t use an Ohmmeter to test wrist straps.
43
Controlling Body Voltage
Non-Linear
Resistance
Skin Resistance is Non-Linear
VERY
MOISTURE
DEPENDENT.
LOTIONS
SOMETIMES
REQUIRED
DC VOLTS
A DMM puts out less than a volt when measuring
ohms; therefore, a good cuff will test as defective.
44
Controlling Body Voltage
Continuous
Monitors
Wrist Strap Continuous Monitors
•
Resistance Measurement Type:
 The system resistance is continuously
monitored during use.
 Resistance Range: 0.8 to 10 Meg ohms
•
Voltage Sensing Type:
 Body Voltage is monitored continuously.
 Acceptable Voltage Range: 0 to +/-10V
45
Controlling Body Voltage
Dual Wire Cords
Wrist Strap Continuous Monitors
• Both types require dual wire cords
and special wrist strap cuffs.
46
Controlling Body Voltage
Footwear
Testing
• Footwear Testing
– Refer to ESD STM97.1-1999
– Demonstrate Footwear Test with:
 Integrated wrist strap / footwear
tester
 Portable Flooring Megger
• Demonstrate the Footwear Test
– Combat Boots
– ESD Shoes
– Stocking Feet
47
Controlling Body Voltage
Footwear/Floor
System
Lab Data on Max Body Voltage
Without Wrist Strap
• On Nylon Carpet
• With Combat Boots
• With ESD Shoes
Actual Lab Data
At 10 % RH
- 840 V
215 V
• On ESD Carpet
• With Combat Boots
• With ESD Shoes
558 V
41 V
Good ESD control requires a
complete system approach!
48
Packaging
•
Packaging, 1st of 8
SUMMARY OF ESD CONTROL.
STRATEGIES.
– RULE 1.
Handle all ESD Sensitive items at an ESD.
Workstation.
– RULE 2.
Transport and store all ESDS items ( both.
reparable and serviceable) in static.
shielding and non-charge generating.
packages or containers.
TO 00-25-234 Chapter 7, 7-5.b
49
Packaging
Objectives
ESD Packaging Objectives
– Provides Shielding
– Immune to Tribocharging
– Allow charge transfer from
package exterior to an ESD
protective worksurface
50
Packaging
Types 1, 2, & 3
Mil-Prf-81705D for ESD Protective,
Heat-Sealable, Barrier Materials
– A Navy Spec 3 Sep 98
Three Types:
– Type I Not transparent, Water-vapor proof, ESD
protective, EMI and ESD shielding. Heavy duty.
– Type II Transparent, Waterproof, ESD protective and
dissipative. Pink Poly fits here.
– Type III Transparent, Waterproof, ESD protective and
static shielding
51
Packaging
Type 1, details
• EMI/Static Shield Bag (Type I)
– Top of the Line, heavy duty outer wrap.
– Required for long
term storage.
– Protects from
water vapor &
Electromagnetic
Fields.
– ESD Protective.
52
Packaging
Type 2, details
• Pink Poly Bags (Type II).
– Pink Polyethylene reduces tribocharging.
– Does not provide.
good ESD protection.
– Is used to protect.
from physical damage.
Shown: Zip Lock Bubble.
Wrap.
53
Packaging
Type 3, Details
• Static Shielding Bag (Type III)
– Transparent, Local use, Shielding bag
 Reduces need to open bags
– Water proof
(not vapor proof)
– Protects from
Electrostatic fields
(not magnetic fields)
– Dissipates a Charge
54
Packaging
Materials to Avoid
• Avoid Unnecessary
Charge Generators
– Styrofoam materials
– Clear Polyethylene and
Polypropylene films
and bags
55
Packaging
Packaging, Demos
• Demonstrate the Properties of
the three types of bags:
– Transparency
– Tribocharging
– ESD Shielding
This is not a
Faraday Cage !
– EMI Shielding
– Puncture Resistance
– Vapor and water Resistance
56
Packaging
• When does ESD susceptibility stop?
– When ESD sensitive items are properly packaged
in ESD control packaging materials.
– When the level of assembly or packaging is such
that a complete electrostatic shield (Faraday
Cage) exists around the item.
Faraday Cage Examples:
ESD Shielding Bag/Pouch, Conductive Tote Box (with lid),
Conductive Case/Enclosure
57
Cabinets, Shelves, & Work Surfaces
• Cabinets, Shelves, & Work Surfaces
Requirements:
– Ground cabinets, shelves, and work surfaces used during
handling or storage of ESD sensitive items.
– All ESD control work surfaces, storage cabinets, and
shelves shall be tested annually.
 Non ESD designed shelves and storage cabinets may
require fitted ESD work surface material to meet this
requirement.
– Cabinets and shelves used exclusively for storage of non
ESD Sensitive items (or ESD Sensitive items protected by
a complete Faraday Cage) do not require a ground
connection or periodic testing.
58
ESD Connector Caps
• Connector Caps, NASM5501/31 & 32
Formerly Mil-C-5501/31A & 32A
– They complete the Faraday Cage
 They protect against discharge to the pins.
 They keep moisture and dust out.
– They need to be conductive to work.
 Pink Poly will not work
 None of the colored ones will protect electronics
– They can be tested with a DMM
– There is a supply problem
 Some are not labeled correctly.
59
Marking, Labeling, & Signs
Marking & Signs, 1st of 4
• Equipment Label
–
–
TO 00-25-234, Fig 7-8
Attach on a readily visible exterior surface,
if space is available and does not hinder
operation of the item.
60
Marking, Labeling, & Signs
Unit Pack Label
• The Unit Pack Label
–
–
TO 00-25-234, Fig 7-11
Attach to both sides of outermost bag.
ATTENTION
STATIC SENSITIVE DEVICES
HANDLE ONLY AT
STATIC SAFE WORK STATIONS
61
Marking, Labeling, & Signs
Shipping Container Label
• Shipping Container Label
–
TO 00-25-234, Fig 7-12
– Attach to Fast-Pack, Intermediate Pack,
Exterior Pack, or Shipping Container which
contain the unit packs.
– The preferred color
scheme is shown.
62
Marking, Labeling, & Signs
ESD Work Area Sign
• ESD Work Area Sign
–
–
TO 00-25-234, Fig 7-16
Placed at or near the entrance to ESD
Work Area.
ATTENTION
STATIC SAFEGUARDED
WORK AREA
63
ESD Worksurfaces
ESD Worksurfaces, 1st
of 4
• TYPES OF ESD WORKSURFACES
– RIGID
 None approved at this time
» They have smooth hard surfaces, but do not
dissipate charge at low humidity.
– CUSHIONED
 These are most commonly used.
» Available in standard 2 x 4’ size (Table 7-3 item 16)
» The 40’ Roll, Item 19 in Table 7-3, does about 10
work benches
– FOLDABLE
 These are portable and have CPG & W/S
64
ESD Worksurfaces
Permanent Type
• Permanent ESD Workstation Surface.
– Glued to the wood subsurface.
 Prevents sliding and buckling of the surface.
– Durable hard rubber increases service life.
 Surface hardness is between Rigid and Cushioned.
– Passes AF’s static dissipation, and resistance.
tests.
Refer to items 1 - 12
in Table 7-3
65
ESD Worksurfaces
• What to do with a non ESD Workstation?
– Add a 2 x 4’ ESD control work surface.
 Sits on top of existing surface.
 Reduces cost of replacing entire workstation
– Reference Table 7-3, item 13 in T.O. 00-25-234.
66
ESD Worksurfaces
Cleaning them
• CLEANING WORKSURFACES.
– Best to use 70 / 30 IPA / water.
 Do not use any silicones !
 Do not use oils or waxes !
•
Demonstrate Testing the Work Surface.
–
Test Annually or sooner if desired.
 The Work Surface Test Procedure is in 7-8 a.
» A Megohmmeter and a 5 LB electrode is used.
» Test points from the surface to the CPG.
67
ESD Worksurfaces
Scrim Layer Functions
• Scrim Layer Functions
– Provides a uniform top to top resistance
– It is part of the grounding system
• Test
–
the electrical contact from Snap to Scrim
Use a DMM or Megger across the Snaps
Insulative, Protective, Transparent Paper Layer
Humectants, Metal particles, Salts, Ionic Materials
The Colored Decorative Paper
Layer
The Conductive Scrim layer, usually carbon doped paper
Cardboard Layer #1 for strength and thickness
Cardboard Layer #2 for strength and thickness
68
Air
Ionizers,
what they
do
AIR IONIZATION
IONIZED AIR REMOVES CHARGES
– FROM JOB ESSENTIAL NON CONDUCTORS
 PACKAGING MATERIALS
 LAMINATED SCHEMATICS & DRAWINGS
– AND FROM ISOLATED CONDUCTORS
– NEED TO MAINTAIN A BALANCE OF
POSITIVE & NEGATIVE IONS
69
AIR IONIZATION
When to use Ionizers
• Use
When:
– The Work Area Survey requires it.
• Demonstrate Value of Ionization:
Ionizers require
periodic testing.
Refer to 00-25-234
7-7.d.6.a
70
Grounding
Grounding, 1st of 5
• View of Open Outlet Box Showing Equipment
Grounding Conductors.
Equipment
Grounding
Conductors
Third Wire
“Ground”
71
Grounding
Wiring Verification Test
•photo
Utility Wiring Verification Test is done first.
Par. 7-5.e(3)(b) of T.O. 00-25-234.
72
Grounding
Utility Ground Check
• Utility Ground Wiring Verification Check,
Par. 7-5.e(3)(c)
• Item 66 of
Table 7-3
73
Grounding
Bench Ground Check
• Resistance Check from Bench’s Groundable point to
third wire
ground.
Par. 7-5.e(3)(d)
74
Grounding
Common Point Ground
• USE AN OHMMETER TO CHECK
CONTINUITY FROM THE CPG TO:
WRIST STRAP
PLUG-INS,
BENCH
DRAWERS,
BENCH MATS,
SHELF MATS
75
The Role of Capacitance
CAPACITANCE
A KEY PLAYER IN ESD
76
The Role of Capacitance
Capacitance Equations
CAPACITANCE EQUATIONS
Q = CV
C=Q/V
V=Q/C
Q - charge in coulombs
C - Capacitance in farads
V - potential in volts
Nanocoulomb (nc) = 10-9 C
Picofarad (pF) = 10-12 F
77
The Role of Capacitance
Parallel Plate Example
Parallel Plate Capacitance
A
d
• Capacitance becomes larger
as the distance becomes less.
• Let Q (coulombs) remain
constant.
• The Voltage goes down
as the capacitance goes up.
A
C = --- 0K
d
C = Farads
A = meters2
d = meters
0 = 8.85 x 10-12 f/m
K = dielectric constant
V=Q/C
78
The Role of Capacitance
Your Capacitance
A PRACTICAL EXAMPLE OF CAPACITANCE AT WORK
• If you have insulative shoes, your soles become the
dielectric in a capacitor between you and the
grounded floor.
• With a charge on your body lift your leg high.


What happens in terms of the equations ?
What happens to the voltage on your body ?
79
Reference
Reference, 1st of 4
• Measuring Charge, Coulombs
Faraday Cup
Electrometer
80
Reference
Energy Equations
E = 1/2 C V 2
E = 1/2 Q V
E = 1/2 Q 2 / C
E = energy in Joules
C = Capacitance in Farads
V = Volts DC
81
Reference
Numerical Prefixes
FACTOR
12
10
9
10
6
10
3
10
-3
10
-6
10
-9
10
- 12
10
Examples:
PREFI X
t era
gi ga
me g a
ki l o
mi l l i
mi c r o
na no
pi c o
SYMBOL
T
G
M
k
m
u
n
p
1 nanocoulomb = 1 x 10 -9 coulombs
10 picofarad = 10 x 10-12 farads
82
Reference
Useful Derived Units
QUANTITY
NAME
force
Newton
N
Kg/m/s-2
charge
coulomb
Q
A/s
energy
joule
J
N/m
power
watt
W
J/s
E
N/C - V/m
field strength
SYMBOL EXPRESSION
voltage potential
volt
V
J/C
capacitance
farad
C
Q/V
resistance
ohm

V/A
bulk resistivity
P
 - m
surface resistivity
Ps
Square
83
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ESD Contacts
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85