[email protected](c) 2000 doug mason1 esd thoughts and theories esd things i think about (rev....
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(c) 2000 Doug Mason 1
ESD Thoughts and theoriesESD Thoughts and theoriesESD Thoughts and theoriesESD Thoughts and theories
ESD things I think about (Rev. 1)ESD things I think about (Rev. 1)
Do you have other ESD topics we should clarify better?Do you have other ESD topics we should clarify better?
ESD things I think about (Rev. 1)ESD things I think about (Rev. 1)
Do you have other ESD topics we should clarify better?Do you have other ESD topics we should clarify better?
Graphics I did not create are ©1999 New Vision Technologies Inc.
(c) 2000 Doug Mason 2
IntroductionIntroductionIntroductionIntroduction
I am a soldering trainer who focuses on the management of the I am a soldering trainer who focuses on the management of the total process that impacts on the quality of the solder joint, from total process that impacts on the quality of the solder joint, from design to delivery.design to delivery.
One aspect I cover is the management of ESD. In researching One aspect I cover is the management of ESD. In researching this topic, I am running into explanations that would not satisfy this topic, I am running into explanations that would not satisfy my audience, who are: Process Workers, Stores people, my audience, who are: Process Workers, Stores people, Purchasers, Managers, and so on.Purchasers, Managers, and so on.
They do not want explanations that require an understanding of They do not want explanations that require an understanding of Laws of Physics or any mathematics, formulae, and so on. Laws of Physics or any mathematics, formulae, and so on. Explanations must be clear, simple and obvious, related to their Explanations must be clear, simple and obvious, related to their everyday experiences.everyday experiences.
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IntroductionIntroductionIntroductionIntroduction
I want to know if my explanations make sense and I want to know if my explanations make sense and are correct.are correct.
Even if I am wrong, hopefully I am a catalyst for the Even if I am wrong, hopefully I am a catalyst for the generation of more lucid and logical simple generation of more lucid and logical simple explanations that are understandable by the widest explanations that are understandable by the widest community.community.
When such people understand the reasons they need When such people understand the reasons they need to take such steps, this should surely help them to take such steps, this should surely help them implement the required strategies.implement the required strategies.
(c) 2000 Doug Mason 4
IntroductionIntroductionIntroductionIntroduction
I am interested in hearing from people who want to I am interested in hearing from people who want to make positive contributions.make positive contributions.
When you write, please tell me the Revision number When you write, please tell me the Revision number (see the first Title Slide)(see the first Title Slide)
If you can make a useful contribution to my knowledge, If you can make a useful contribution to my knowledge, please do so. My address is [email protected] do so. My address is [email protected]
Many thanks,Many thanks,
DougDoug
(c) 2000 Doug Mason 5
First, some basic principles . . .First, some basic principles . . .First, some basic principles . . .First, some basic principles . . .
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Atomic TheoryAtomic TheoryAtomic TheoryAtomic Theory
Basic Principles (1)Basic Principles (1)Basic Principles (1)Basic Principles (1)
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An atom is made up of chargesAn atom is made up of chargesAn atom is made up of chargesAn atom is made up of charges
An atom is made up of An atom is made up of charges.charges.
In its stable state, the size of In its stable state, the size of the positive charge at the the positive charge at the centre (nucleus) of an atom is centre (nucleus) of an atom is balanced by the size of all the balanced by the size of all the negative charges of the negative charges of the electrons, making it neutral electrons, making it neutral overall.overall.
The electrons whirl around The electrons whirl around the centre like planets.the centre like planets.
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Creating a charge imbalanceCreating a charge imbalanceCreating a charge imbalanceCreating a charge imbalance
When an atom When an atom losesloses an an electron, it has a charge electron, it has a charge imbalance.imbalance.
Since this atom has Since this atom has lostlost an an electron, which is a negative electron, which is a negative charge, the atom is now a charge, the atom is now a positive charge.positive charge.
When it When it gainsgains an extra an extra electron, an atom becomes a electron, an atom becomes a negative charge.negative charge.
Electron “lost”
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A dischargeA dischargeA dischargeA discharge
This movement of charges is This movement of charges is called a called a dischargedischarge..
When something which has When something which has a charge imbalance is a charge imbalance is brought close to or touches brought close to or touches something else, a stream of something else, a stream of charges might move, to try charges might move, to try to bring the atoms back to to bring the atoms back to their stable balanced their stable balanced condition.condition.
This powerful, rapid movement of charges can damage electronic
components.
Let’s see it again!
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Triboelectric generationTriboelectric generationTriboelectric generationTriboelectric generation
Basic Principles (2)Basic Principles (2)Basic Principles (2)Basic Principles (2)
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When two materials are in intimate contact, they share electrons which are at their surfaces.
When materials are in contact
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When two materials are in intimate contact, they share electrons which are at their surfaces.
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
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It is possible for electrons to be “stolen” from one material by nuclei in the other material, because they
have a stronger force
When materials are in contact
Since the contacting surfaces still have an equal number of positive and negative charges, there is no overall
charge imbalance on them.
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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”
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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.
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.
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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 the materials are separated
Electrons “lost”
Electrons “gained”
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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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.
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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.
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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.
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The drier the air (lower relative humidity, RH) the higher the generated charge.
When the materials are separated
Electrons “lost”
Electrons “gained”
Separating similar materials can still produce a charge, such as when a smooth surface is separated from a rough surface (large rolls of plastic in the Store).
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The creation of a charge when The creation of a charge when materials are separated is termed materials are separated is termed
“triboelectric charging”“triboelectric charging”
The creation of a charge when The creation of a charge when materials are separated is termed materials are separated is termed
“triboelectric charging”“triboelectric charging”
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Charging by InductionCharging by InductionCharging by InductionCharging by Induction
Basic Principles (3)Basic Principles (3)Basic Principles (3)Basic Principles (3)
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Charging by inductionCharging by inductionCharging by inductionCharging by induction
An explanation of the principle, as I understand it.An explanation of the principle, as I understand it. This is required for the explanation of scenarios I This is required for the explanation of scenarios I
describe - (1) walking on carpet and (2) developing a describe - (1) walking on carpet and (2) developing a charge while driving.charge while driving.
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Charging by inductionCharging by induction
The presence of this very strong force causes similar charges The presence of this very strong force causes similar charges on the surfaces of nearby conductors to be repelled.on the surfaces of nearby conductors to be repelled.
The charge imbalance on a surface produces an electric field. The charge imbalance on a surface produces an electric field.
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Charging by inductionCharging by induction
If the conductor is grounded while it is still influenced by the If the conductor is grounded while it is still influenced by the electric field, these repelled charges go to earth, thus electric field, these repelled charges go to earth, thus maintaining a charge balance in the areas of the conductor maintaining a charge balance in the areas of the conductor that are not affected by the electric field.that are not affected by the electric field.
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Charging by inductionCharging by induction
When the earth is removed and then the electric field is When the earth is removed and then the electric field is removed, the conductor has become charged to the opposite removed, the conductor has become charged to the opposite
charge of the original source.charge of the original source.
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Walking on carpetWalking on carpetWalking on carpetWalking on carpet
Thoughts and theories (1)Thoughts and theories (1)Thoughts and theories (1)Thoughts and theories (1)
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Walking on carpetWalking on carpetWalking on carpetWalking on carpet
In one place, I read that as I walked on carpet, electrons In one place, I read that as I walked on carpet, electrons moved from the bottom of my shoe and up my leg, to create moved from the bottom of my shoe and up my leg, to create the charge on my body. My question became: “If that path the charge on my body. My question became: “If that path exists, why is there then a need for a heel/foot strap to remove exists, why is there then a need for a heel/foot strap to remove those same electrons back to ground potential?”those same electrons back to ground potential?”
My current theory is described in the next few slides.My current theory is described in the next few slides. I have not tested it, nor do I know how I would do it.I have not tested it, nor do I know how I would do it. This explanation shows why I showed the principle of This explanation shows why I showed the principle of
“charging by induction” on the previous slides.“charging by induction” on the previous slides.
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Walking across carpetWalking across carpetWalking across carpetWalking across carpet
Walking across a carpet Walking across a carpet creates a charge creates a charge imbalance on the lower imbalance on the lower surface of my shoes.surface of my shoes.
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A strong electric fieldA strong electric fieldA strong electric fieldA strong electric field
This charge imbalance This charge imbalance creates a strong electric creates a strong electric field that emanates in all field that emanates in all directions.directions.
The material in the sole The material in the sole of my shoe enables a of my shoe enables a strong field to influence strong field to influence charges within my foot.charges within my foot.
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An induced chargeAn induced chargeAn induced chargeAn induced charge
Since my body is relatively Since my body is relatively conductive, the charges conductive, the charges that are repelled from the that are repelled from the lower regions of my foot set lower regions of my foot set up a charge throughout the up a charge throughout the rest of my body.rest of my body.
But my body still has a But my body still has a balanced charge overall (it balanced charge overall (it has not lost or gained any has not lost or gained any charges).charges).
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Contacting a source of chargesContacting a source of chargesContacting a source of chargesContacting a source of charges
While I am still on the While I am still on the carpet (still influenced by carpet (still influenced by the electric field on the the electric field on the sole of my shoe), I briefly sole of my shoe), I briefly touch a metallic object (a touch a metallic object (a chair, table, door knob, chair, table, door knob, metal stapler, etc.)metal stapler, etc.)
This enables charges to be This enables charges to be provided by the metallic provided by the metallic object.object.
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Charging through the airCharging through the airCharging through the airCharging through the air
This movement of charges is This movement of charges is thus producing an overall thus producing an overall charge imbalance in my charge imbalance in my body, since I was previously body, since I was previously neutral overall.neutral overall.
If the charge imbalance on If the charge imbalance on my body is large enough, I my body is large enough, I do not need to touch the do not need to touch the object, as the imbalance object, as the imbalance could allow a movement of could allow a movement of charges through the air.charges through the air.
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An overall charge imbalanceAn overall charge imbalanceAn overall charge imbalanceAn overall charge imbalance
Therefore, after that Therefore, after that brief encounter with brief encounter with the metallic object, the metallic object, my body now has an my body now has an overall charge overall charge imbalance.imbalance.
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Removing that chargeRemoving that chargeRemoving that chargeRemoving that charge
The only way to remove the possibility of damaging The only way to remove the possibility of damaging an ESD-sensitive device or assembly is to remove an ESD-sensitive device or assembly is to remove the overall charge imbalance on my body.the overall charge imbalance on my body.
This is done by connecting my body to the ready This is done by connecting my body to the ready source of charges that is at the same reference source of charges that is at the same reference potential as the item I wish to handle - using a wrist potential as the item I wish to handle - using a wrist strap or foot strap.strap or foot strap.
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Driving a carDriving a carDriving a carDriving a car
Thoughts and theories (2)Thoughts and theories (2)Thoughts and theories (2)Thoughts and theories (2)
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I am having no small difficulty developing a model which describes I am having no small difficulty developing a model which describes the actions that result in a charge imbalance being created on a the actions that result in a charge imbalance being created on a person while they drive a car.person while they drive a car.
Charge imbalances are created by the movement of the driver’s body Charge imbalances are created by the movement of the driver’s body against their clothing, by the movement of that clothing against the against their clothing, by the movement of that clothing against the car seat and is increased by the action of leaving the seat.car seat and is increased by the action of leaving the seat.
I assume that the nett induced electric field and the (small) I assume that the nett induced electric field and the (small) triboelectric effect on the skin determine the charge imbalances triboelectric effect on the skin determine the charge imbalances developed on the surfaces of the driver’s back and tail. The types of developed on the surfaces of the driver’s back and tail. The types of materials worn by the driver and the material used on the car seat materials worn by the driver and the material used on the car seat have the greatest impact on determining the size of the electric field have the greatest impact on determining the size of the electric field that impacts the driver’s back and tail.that impacts the driver’s back and tail.
Charged while driving a car (part 1)Charged while driving a car (part 1)Charged while driving a car (part 1)Charged while driving a car (part 1)
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Charged while driving a car (part 2)Charged while driving a car (part 2)Charged while driving a car (part 2)Charged while driving a car (part 2)
This shows that the body does not assume a significant overall This shows that the body does not assume a significant overall charge imbalance. Maybe there is a potential gradient caused charge imbalance. Maybe there is a potential gradient caused by the presence of the charge near the driver’s back and tail, by the presence of the charge near the driver’s back and tail, with the driver’s fingers assuming an opposite potential, as the with the driver’s fingers assuming an opposite potential, as the charges are driven from the field induced by the seat, and the charges are driven from the field induced by the seat, and the fingers are outside that electric field. This is what I have fingers are outside that electric field. This is what I have assumed.assumed.
This would mean, as I have described, that the observed This would mean, as I have described, that the observed “discharge” between the person and the car body is actually a “discharge” between the person and the car body is actually a neutralisation of those charges on the fingers, and this is thus neutralisation of those charges on the fingers, and this is thus the time that the body receives an actual overall charge.the time that the body receives an actual overall charge.
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Charged while driving a car (part 3)Charged while driving a car (part 3)Charged while driving a car (part 3)Charged while driving a car (part 3)
Do the charges on the seat cover actually travel to the driver’s Do the charges on the seat cover actually travel to the driver’s skin through the material, at an atomic level? Or is this, as I skin through the material, at an atomic level? Or is this, as I have described, a charge induced on the driver’s back?have described, a charge induced on the driver’s back?
I need a description that can be understood by a reasonable I need a description that can be understood by a reasonable Process Worker - no maths, no “in-terms” - just a plain Process Worker - no maths, no “in-terms” - just a plain English description that relies on basic concepts.English description that relies on basic concepts.
This is all relevant to the creation and management of a This is all relevant to the creation and management of a charge by an Electronics Assembler at their workplace.charge by an Electronics Assembler at their workplace.
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I am driving my carI am driving my carI am driving my carI am driving my car
As I drive my car, there is As I drive my car, there is constant movement between my constant movement between my clothes and my car seat, and clothes and my car seat, and between my body and my between my body and my clothes.clothes.
These movements create charge These movements create charge imbalances on the surfaces of my imbalances on the surfaces of my clothes and my skin.clothes and my skin.
These imbalances set up strong These imbalances set up strong electric fields that affect charge electric fields that affect charge distribution in my body.distribution in my body.
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Charge distributionCharge distributionCharge distributionCharge distribution
Charge imbalances (and Charge imbalances (and strong electric fields) strong electric fields) appear at the:appear at the:
– outer surface of my clothesouter surface of my clothes
– parts of my body that are parts of my body that are influenced by the strong influenced by the strong electric field (opposite electric field (opposite polarity to the source)polarity to the source)
– remote exposed parts of my remote exposed parts of my body (same polarity as the body (same polarity as the source of the originating source of the originating charge imbalance)charge imbalance)
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Further charging as I leave the carFurther charging as I leave the carFurther charging as I leave the carFurther charging as I leave the car
Further triboelectric Further triboelectric activity occurs as I turn to activity occurs as I turn to get out of the car.get out of the car.
Also, the Voltage of the Also, the Voltage of the charge increases when I charge increases when I stand up, since my body stand up, since my body now presents a smaller now presents a smaller area relative to the ground.area relative to the ground.
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A discharge before exitingA discharge before exitingA discharge before exitingA discharge before exiting
If, before leaving the car, I touch a If, before leaving the car, I touch a ready source of charges (such as the ready source of charges (such as the metal door handle), the charges enter metal door handle), the charges enter my body to balance the charge my body to balance the charge imbalance on my fingers.imbalance on my fingers.
This discharge creates an overall This discharge creates an overall charge imbalance on my body.charge imbalance on my body.
This imbalance declines as the charge This imbalance declines as the charge on my clothes decline and I continue on my clothes decline and I continue to touch sources of ready charges to touch sources of ready charges while this is occurring.while this is occurring.
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Not discharging before leavingNot discharging before leavingNot discharging before leavingNot discharging before leaving
However, if I touch only non-However, if I touch only non-conductors as I leave the car, conductors as I leave the car, the charge distribution the charge distribution continues on my body for as continues on my body for as long as the charge imbalance long as the charge imbalance remains on the outer surface remains on the outer surface of my clothing.of my clothing.
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Discharging to the car bodyDischarging to the car bodyDischarging to the car bodyDischarging to the car body
In this case, it is likely there In this case, it is likely there will be a movement of will be a movement of charges between my body charges between my body and a source of ready and a source of ready charges (such as the car charges (such as the car body).body).
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It’s the same at your work placeIt’s the same at your work placeIt’s the same at your work placeIt’s the same at your work place
If you are not provided with an ESD-safe chair at your If you are not provided with an ESD-safe chair at your work place, the same actions occur as with the car driver.work place, the same actions occur as with the car driver.
Even though in most instances you do not feel the discharge Even though in most instances you do not feel the discharge as you leave your car, it is likely that one exists.as you leave your car, it is likely that one exists.
The sensitivity level of many electronic components means The sensitivity level of many electronic components means that they can be affected by a discharge produced by the that they can be affected by a discharge produced by the seat where you work, even though you do not feel it.seat where you work, even though you do not feel it.
The only safe way is to always wear a properly connected The only safe way is to always wear a properly connected and functioning wrist strap.and functioning wrist strap.
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Is a smock a Faraday Cage?Is a smock a Faraday Cage?Is a smock a Faraday Cage?Is a smock a Faraday Cage?
Thoughts and theories (3)Thoughts and theories (3)Thoughts and theories (3)Thoughts and theories (3)
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A smock as a Faraday Cage?A smock as a Faraday Cage?A smock as a Faraday Cage?A smock as a Faraday Cage?
I consistently read that an ESD smock functions as a Faraday I consistently read that an ESD smock functions as a Faraday Cage.Cage.
I also read that a Faraday Cage is a hollow conductor that I also read that a Faraday Cage is a hollow conductor that distributes its charge imbalance on its outer surface, a fact distributes its charge imbalance on its outer surface, a fact made use of in the shielding bag and tote box.made use of in the shielding bag and tote box.
But, I reason, if a smock holds its charges on its outer surface, But, I reason, if a smock holds its charges on its outer surface, surely this is bringing it close to the components and surely this is bringing it close to the components and assemblies being worked on, which is not wanted.assemblies being worked on, which is not wanted.
Or have I missed the point, is the inside of the garment the Or have I missed the point, is the inside of the garment the outside of the Cage?outside of the Cage?
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A hollow conductorA hollow conductorA hollow conductorA hollow conductor
A Faraday Cage is a A Faraday Cage is a hollow conductor.hollow conductor.
Michael Faraday
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Charges sit on the Charges sit on the outsideoutsideCharges sit on the Charges sit on the outsideoutside
When a Faraday Cage is When a Faraday Cage is placed in an electric placed in an electric field, the charges sit on field, the charges sit on the the outsideoutside of the of the conductive surface, and conductive surface, and the field does not the field does not penetrate it.penetrate it.
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Two practical applicationsTwo practical applicationsTwo practical applicationsTwo practical applications
This fact is made use of in:This fact is made use of in:– the static shielding bag, the static shielding bag,
which has a continuous which has a continuous conductive layer,conductive layer,
– the tote box, made of the tote box, made of conductive material.conductive material.
If there is an opening in the If there is an opening in the conductive layer, some of conductive layer, some of the electric field may pass the electric field may pass through it.through it.
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The “outside” of a Faraday CageThe “outside” of a Faraday CageThe “outside” of a Faraday CageThe “outside” of a Faraday Cage
The “outside” The “outside” surface of a Faraday surface of a Faraday Cage is the surface Cage is the surface that is closest to the that is closest to the electric field.electric field.
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A field placed inside a Faraday CageA field placed inside a Faraday CageA field placed inside a Faraday CageA field placed inside a Faraday Cage
When there is an electric When there is an electric field field insideinside a Faraday Cage, a Faraday Cage, the “outside” of the the “outside” of the conductor is thus the inner conductor is thus the inner surface of the Cage.surface of the Cage.
An electric field An electric field insideinside a a Faraday Cage does not Faraday Cage does not penetrate it, unless the penetrate it, unless the continuity of the conductive continuity of the conductive layer is broken.layer is broken.
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Smock has a conductive layerSmock has a conductive layerSmock has a conductive layerSmock has a conductive layer
An ESD smock has a An ESD smock has a continuous conductive layer.continuous conductive layer.
This forms a Faraday Cage This forms a Faraday Cage around the wearer.around the wearer.
The electric field is inside the The electric field is inside the garment.garment. (Given the nature of (Given the nature of material, the term “outer” material, the term “outer” could be seen as being quite could be seen as being quite arbitrary, anyway.)arbitrary, anyway.)
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The need for a complete layerThe need for a complete layerThe need for a complete layerThe need for a complete layer
Electric fields resulting Electric fields resulting from charge imbalances from charge imbalances produced by the wearer produced by the wearer do not pass through the do not pass through the conductive layer - unless conductive layer - unless the layer is not complete the layer is not complete (for example - if it is (for example - if it is unbuttoned or cuffs unbuttoned or cuffs protrude).protrude).
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Sources of internal fields Sources of internal fields Sources of internal fields Sources of internal fields Most movement occurs Most movement occurs
with the arms, so the with the arms, so the sleeves carry the sleeves carry the strongest fields. These strongest fields. These fields are continually fields are continually varying.varying.
The electric fields from The electric fields from clothing not covered by clothing not covered by the Faraday Cage (such the Faraday Cage (such as exposed sleeve cuffs) as exposed sleeve cuffs) enter the work area.enter the work area.
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Garments are dissipativeGarments are dissipativeGarments are dissipativeGarments are dissipative
The high resistance of The high resistance of the outer layer of the outer layer of smocks is similar to that smocks is similar to that of dissipative mats.of dissipative mats.
This controls the This controls the removal rate of any removal rate of any charges, whether the charges, whether the imbalance is outside the imbalance is outside the garment or inside it.garment or inside it.
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Garments are anti-staticGarments are anti-staticGarments are anti-staticGarments are anti-static
The garments are also The garments are also anti-static, meaning that anti-static, meaning that they resist the creation they resist the creation of charge imbalances.of charge imbalances.
The panels are sewn The panels are sewn with material that with material that ensures they are ensures they are electrically connected.electrically connected.
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ESD Thoughts and theoriesESD Thoughts and theoriesESD Thoughts and theoriesESD Thoughts and theories
ESD things I think about (Rev. 1)ESD things I think about (Rev. 1)
Do you have other ESD topics we should clarify better?Do you have other ESD topics we should clarify better?
ESD things I think about (Rev. 1)ESD things I think about (Rev. 1)
Do you have other ESD topics we should clarify better?Do you have other ESD topics we should clarify better?
Graphics I did not create are ©1999 New Vision Technologies Inc.