Transcript ElectroStatic Discharge

ElectroStatic Discharge
The mystery and how to live with it
By Ray Richter
Static Electricity
 Lightning is probably the most recognizable
effect of static electricity. Generating millions
and millions of voltage and we all know the
damage lightning can do to property and
people.
 Another recognizable effect of static electricity
is the shock you receive when you slid out of
a car in dry weather conditions and feel a
zap. The human body feels a shock when
the voltage is higher than about 3,500 volts.
Static Electricity
 Here's another
problem with the usual
"static electricity"
concept. First, think
about everyday matter.
 Molecules have
protons and electrons,
unbalanced electron
shells always try to
balance.
"STATIC ELECTRICITY" IS CAUSED
BY FRICTION? WRONG.
 "Static" electricity appears whenever two
dissimilar insulating materials are placed into
intimate contact and then separated again. All
that's required is the touching.
 Chemical bonds are formed when the surfaces
touch, and if the atoms in one surface tend to hold
electrons more tightly, that surface will tend to
steal charged particles from the other surface
immediately as they touch.
"STATIC ELECTRICITY" IS CAUSED
BY FRICTION? WRONG.
 One surface now has more electrons than protons,
while the other has more protons than electrons.
 When the surfaces are later separated, the regions
of opposite charge-imbalance also get separated.
 For example, when adhesive tape is placed on an
insulating surface and then peeled off, both the
tape and the surface will become electrified. No
friction was required.
Static Electricity (cont)
 Walking over a carpet can generate
35,000 volts. The Electrostatic
Discharge (ESD) from this voltage can
cause pain. The discharge is not life
threatening but it still hurts.
Static Electricity (cont)
 The static electricity that concerns the
electronics industry is the discharge that you
can neither feel nor see.
 The static electricity that concerns the
Petroleum industry is the discharge that you
may not feel but may see.
 Difference is the voltage and POWER (watts)
Spark Gap
mm gap
0.5
1
2
3
4
5
Min volts
2850
4350
7350
10350
13350
16350
Any voltage above the
minimum is converted into
current. This where the
potential power comes in.
Static Electricity Clothing
 Their measurements for different clothing
and various car-seats give impressively high
voltages, and this occurred at humidity
levels above 50%. The voltages should be
MUCH higher at, say 5% R.H.!
 Nylon clothes: 21,000 volts (Ouch!)
 Wool clothes: 9,000 volts
 Cotton clothes: 7,000 volts
Static Electricity
and Daily movements
Table 1
TYPICAL ELECTROSTATIC VOLTAGES*
RELATIVE HUMIDITY
EVENT
10%
40%
55%
Walking across carpet
35,000
15,000
7,500
Walking across vinyl floor
12,000
5,000
3,000
Motions of bench worker
6,000
800
400
Remove Material from plastic tubes
2,000
700
400
Remove Material from vinyl trays
11,500
4,000
2,000
Remove Material from Styrofoam
14,500
5,000
3,500
Remove bubble pack from Material
26,000
20,000
7,000
Pack Material in foam-lined box
21,000
11,000
5,500
Triboelectric Series
Acquires
Human
Hands a more positive charge +
Asbestos
Rabbit Fur
Acetate
Glass
Mica
Human Hair
Nylon
Wool
Fur
Lead
Silk
Aluminum
Paper
Cotton
Steel
Wood
Amber
Sealing Wax
Hard Rubber
MYLAR
Nickel
Copper
Silver
UV Resist
Brass, SS
Gold, Platinum
Sulfur
Acetate, Rayon
Celluloid
Polyester
Styrene (Styrofoam)
Orlon
Acrylic
SARAN
Polyurethane
Polyethylene
Polypropylene
PVC (Vinyl)
KEL F
Silicon
Teflon
Silicone Rubber
Acquires a more negative charge -
"STATIC ELECTRICITY" IS
ELECTRICITY WHICH IS STATIC? NO!
 Instead, 'static electricity' is a collection of
different electrical phenomena; phenomena
where...
 The amounts of positive and negative
electric charge within a material are not
perfectly equal.
 Where voltage is high and current is low.
"STATIC ELECTRICITY" IS
ELECTRICITY WHICH IS STATIC? NO!
 Where electrical forces (attraction and
repulsion) are seen to reach across space.
Widely spaced objects may attract or repel
each other. Hair might stand on end!
 Where electric fields (as opposed to
magnetic fields) become very important.
(Electric fields are also called "electrostatic
fields" or "e-fields."
Static Electricity
 Electrostatics is about "charge," and about the
attract/repel forces which electric charge creates.
The motion or "staticness" of the charge is
irrelevant.
 After all, the forces are still there even when the
charges start flowing.
 And charges which are separated or imbalanced
can sometimes flow along, yet the "static" effects
are undiminished when the current begins.
 In other words, it's perfectly possible to create
flows of so-called "static" electricity.
Quick Note of Interest
 The workers on high
tower power lines are
more at risk from the
static buildup on the wires
than from the power in the
lines. The static buildup
(from wind blowing
across the wires) can
cause burns and falls even
when the power in the
lines is off.
ESD DISCHARGE
Controlling your Discharges
 The control of electrostatic discharge is
an important aspect in the
manufacturing, packaging and Shipping
of products.
 The primary method of control is to
ground or use static-bonding (bring to
the same potential) all conductors that
come in contact or near proximity to the
product
ESD DISCHARGE
Controlling your Discharges
 These conductors include humans, tools,
ESD mats, other electronic devices, boards,
connectors, packaging, etc.
 There are other components to a good ESD
Control program including, removal of
unnecessary insulators, adding shielding,
ionization, environmental controls, provide
training, education and top down compliance.
ESD DISCHARGE
Take time to Discharge
Movement times (averaged) from typical operations.
Reaching
Grabbing
Lifting
Relocate
Landing
Time (ms)
455
153
231
924
247
Std. Dev.
(ms)
48
11
61
137
73
The table above shows how long it takes someone to
discharge their static buildup. The times is from the start of
the movement to the end of the movement.
Grounding and/or Bonding
 Grounding: Applying a grounding wire to a
container to eliminate a difference in static charge,
grounding changes the potential between an object
and ground.
 Bonding: Use of a wire between two drums to
eliminate the static charge potential between
objects.
Safe Handling of
Flammable and Combustible Liquids
Explosive Limits
 Explosive limits involve the concentration level of
the given chemical in the air.
 In popular jargon, a vapor/air mixture below the
flammable limit is too lean to burn or explode. A
mixture above the upper flammable limits is too
rich to burn
 Most flammable liquids are volatile, meaning they
evaporate quickly, and can reach a concentration
in air that could lead to an explosion.
Flash Point
 The flashpoint of a fuel is the lowest temperature
at which it can form an ignitable mix with air. At
this temperature the vapour may cease to burn
when the source of ignition is removed. A slightly
higher temperature, the fire point, is defined at
which the vapour continues to burn after being
ignited. Neither of these parameters is related to
the temperatures of the ignition source or of the
burning fuel, which are much higher.
Flammable and Combustible Liquids
Flammable Liquids
Combustible Liquids
Any liquid having a
flashpoint below 100o
F (37.8o C) or lower.
Any liquid having a
flashpoint at or above
100o F (37.8o C).
NFPA Classes IA, IB, &
IC
NFPA Classes II & IIIA
&B
Flammable and Combustible Liquid
Classifications
Flammable Liquid - any liquid having a flashpoint below 100o F
(37.8o C) or higher, the total of which make up 99 percent or more
of the total volume of the mixture. Flammable liquids shall be
known as Class I liquids. Class I liquids are divided into three
classes as follows:
Class IA - shall include liquids having flashpoints below 73 F (22.8
C)
and having a boiling point below 100 F (37.8 C).
Class IB - shall include liquids having flashpoints below 73 F (22.8
C)
And having a boiling point at or above 100 F (37.8 C).
Class IC - shall include liquids having flashpoints at or above 73 F
(22.8 C) and below 100 F (37.8 C).
Flammable and Combustible Liquid
Classifications (Cont.)
Combustible Liquid - any liquid having a flashpoint at or above
100o F (37.8o C). Combustible liquids shall be divided into two
classes as follows:
Class II - shall include those with flashpoints at or above
100 F (37.8 C) and below 140 F (60 C), except any mixture
having components with flashpoints of 200 F (93.3 C) or higher,
the volume of which makes up 99 percent or more of the total
volume of the mixture.
Class III - shall include those with flashpoints at or above
140 F (60 C).
Flammable Liquids
Flashpoint Temperatures
 Triethalemine 17o F
 Enamel Reducer 20o F
 Barsol A-2316 54o F
 Isopropyl Alcohol 45oF
 Acetone Solvent 0o F
 Methanol 45o F
 Barsol A-2343 56o F
 MEK 23o F
 Barsol A-3447 0oF
 Xylene 79o F
 N-Butanol
 Toluene 45o F
36o F
 Sec. Butanol 72o F
 Glycol Ether 94o F
 Gasoline -50o F
 142 Solvent 66/3 610 F
Refueling Incidents
movie
Here is the breakdown of the 20 accidents
involving portable containers for which we
have first-hand reports:
 13 accidents occurred while fueling
metal containers either in the plasticlined bed of a pickup truck (12) or the
carpeted bed of a pickup truck (1). o 4
accidents occurred while filling plastic
containers on the plastic-lined bed of a
pickup truck.
 1 accident occurred while filling a
plastic container that was formerly in
the back of the plastic-lined bed of a
pickup truck.
Continued from prev. page
 1 accident occurred while filling a
plastic pail on the ground.
 1 accident occurred while filling a
metal container on the carpeted
floor of an automobile that had
been driven with the windows
open.
Can flammable or combustible liquids
be hazardous to my body?
 The most obvious harm would be the
danger of a fire or explosion.
 Flammable and combustible liquids can
also cause health problems depending
on the specific material and route of
exposure (breathing the vapour/mist,
eye or skin contact, or swallowing).
 The Material Safety Data Sheet and the
supplier's labels on the containers
should tell you about all the hazards for
the flammable and combustible liquids
that you work with.
Prevention
 Transporting and proper material
handling procedures are typically the
weakest link in an ESD program. Many
companies drop their guard when it
comes to correct packing, handling, and
storage techniques. Adequate protection
requires attention to the details.
Prevention (cont)
 Function of packaging, handling, and storage
products is to limit possible impact of ESD from:
1. triboelectric charge generation
• (Use Grounding and/or Bonding)
2. direct discharge
• (Use Discharge stations, Prevent vapours)
3. electrostatic field
• (Control humidity, use ION generators)
Prevention (cont)
Putting ideals into Practice
1.
Packaging/Transfer Areas
• Remove all non-ESD packaging from area:
Standard bubble wraps, packing peanuts, plastic bags,
Styrofoam.
• Purchasing should insist that all ESDS items be packaged in a
shielded package.
Faraday cages
• Repackage if necessary
•
•
•
•
Use of ESD labels / tape
Heel grounders / ESD floor in transfer areas
Wrist straps for static bonding
Static Bonding clamps and grounding a must do
Prevention (cont)
Putting ideals into Practice
2.
Storage
• Grounded shelving areas with conductive paint.
• Grounding with Ganged Bonding on metal drums.
• Keep areas clean, reduce dust build up.
Metal shielding above stored containers for dust
control.
ESD Protection in the Plant
a.
Awareness
- Training / education
- Signage
b.
Top down
- participation by all levels
operators/supervisors/management
- Must have participation from all levels.
Everyone must understand cost savings and
recognize ESD as QC issue.
- documentation of the reality of ESD