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2000 Doug Mason1 ESD Thoughts and theories ESD things I think about (Rev. 1) Do you have other ESD topics we should clarify.

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Presentation on theme: "2000 Doug Mason1 ESD Thoughts and theories ESD things I think about (Rev. 1) Do you have other ESD topics we should clarify."— Presentation transcript:

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2 Doug Mason1 ESD Thoughts and theories ESD things I think about (Rev. 1) Do you have other ESD topics we should clarify better? ESD things I think about (Rev. 1) Do you have other ESD topics we should clarify better? Graphics I did not create are ©1999 New Vision Technologies Inc.

3 Doug Mason2 IntroductionIntroduction I am a soldering trainer who focuses on the management of the total process that impacts on the quality of the solder joint, from design to delivery. I am a soldering trainer who focuses on the management of the total process that impacts on the quality of the solder joint, from design to delivery. One aspect I cover is the management of ESD. In researching this topic, I am running into explanations that would not satisfy my audience, who are: Process Workers, Stores people, Purchasers, Managers, and so on. One aspect I cover is the management of ESD. In researching this topic, I am running into explanations that would not satisfy my audience, who are: Process Workers, Stores people, Purchasers, Managers, and so on. They do not want explanations that require an understanding of Laws of Physics or any mathematics, formulae, and so on. Explanations must be clear, simple and obvious, related to their everyday experiences. They do not want explanations that require an understanding of Laws of Physics or any mathematics, formulae, and so on. Explanations must be clear, simple and obvious, related to their everyday experiences.

4 Doug Mason3 IntroductionIntroduction I want to know if my explanations make sense and are correct. I want to know if my explanations make sense and are correct. Even if I am wrong, hopefully I am a catalyst for the generation of more lucid and logical simple explanations that are understandable by the widest community. Even if I am wrong, hopefully I am a catalyst for the generation of more lucid and logical simple explanations that are understandable by the widest community. When such people understand the reasons they need to take such steps, this should surely help them implement the required strategies. When such people understand the reasons they need to take such steps, this should surely help them implement the required strategies.

5 Doug Mason4 IntroductionIntroduction I am interested in hearing from people who want to make positive contributions. I am interested in hearing from people who want to make positive contributions. When you write, please tell me the Revision number (see the first Title Slide) When you write, please tell me the Revision number (see the first Title Slide) If you can make a useful contribution to my knowledge, please do so. My address is If you can make a useful contribution to my knowledge, please do so. My address is Many thanks, Doug

6 Doug Mason5 First, some basic principles...

7 Doug Mason6 Atomic Theory Basic Principles (1)

8 Doug Mason7 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.

9 Doug Mason8 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. Electron “lost”

10 Doug Mason9 A discharge This movement of charges is called 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. 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. Let’s see it again!

11 Doug Mason10 Triboelectric generation Basic Principles (2)

12 Doug Mason11 When materials are in contact

13 Doug Mason12 When materials are in contact

14 Doug Mason13 When two materials are in intimate contact, they share electrons which are at their surfaces. When materials are in contact

15 Doug Mason14 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

16 Doug Mason15 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.

17 Doug Mason16 When the materials are separated

18 Doug Mason17 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”

19 Doug Mason18 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.

20 Doug Mason19 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.

21 Doug Mason20 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.

22 Doug Mason21 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.

23 Doug Mason22 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.

24 Doug Mason23 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).

25 Doug Mason24 The creation of a charge when materials are separated is termed “triboelectric charging”

26 Doug Mason25 Charging by Induction Basic Principles (3)

27 Doug Mason26 Charging 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 describe - (1) walking on carpet and (2) developing a charge while driving. This is required for the explanation of scenarios I describe - (1) walking on carpet and (2) developing a charge while driving.

28 Doug Mason27 Charging by induction The presence of this very strong force causes similar charges on the surfaces of nearby conductors to be repelled. The charge imbalance on a surface produces an electric field.

29 Doug Mason28 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.

30 Doug Mason29 Charging by induction When the earth is removed and then the electric field is removed, the conductor has become charged to the opposite charge of the original source.

31 Doug Mason30 Walking on carpet Thoughts and theories (1)

32 Doug Mason31 Walking on carpet 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 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 those same electrons back to ground potential?” 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 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 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 “charging by induction” on the previous slides. This explanation shows why I showed the principle of “charging by induction” on the previous slides.

33 Doug Mason32 Walking across carpet Walking across a carpet creates a charge imbalance on the lower surface of my shoes.

34 Doug Mason33 A strong electric field This charge imbalance creates a strong electric field that emanates in all directions. The material in the sole of my shoe enables a strong field to influence charges within my foot.

35 Doug Mason34 An induced charge Since my 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 my body still has a balanced charge overall (it has not lost or gained any charges).

36 Doug Mason35 Contacting a source of charges While I am still on the carpet (still influenced by the electric field on the sole of my shoe), I briefly touch a metallic object (a chair, table, door knob, metal stapler, etc.) This enables charges to be provided by the metallic object.

37 Doug Mason36 Charging through the air This movement of charges is thus producing an overall charge imbalance in my body, since I was previously neutral overall. 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. 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.

38 Doug Mason37 An overall charge imbalance Therefore, after that brief encounter with the metallic object, my body now has an overall charge imbalance.

39 Doug Mason38 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.

40 Doug Mason39 Driving a car Thoughts and theories (2)

41 Doug Mason40 I am having no small difficulty developing a model which describes the actions that result in a charge imbalance being created on a person while they drive a car. I am having no small difficulty developing a model which describes the actions that result in a charge imbalance being created on a person while they drive a car. Charge imbalances are created by the movement of the driver’s body against their clothing, by the movement of that clothing against the car seat and is increased by the action of leaving the seat. Charge imbalances are created by the movement of the driver’s body against their clothing, by the movement of that clothing against the car seat and is increased by the action of leaving the seat. I assume that the nett induced electric field and the (small) triboelectric effect on the skin determine the charge imbalances 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 have the greatest impact on determining the size of the electric field that impacts the driver’s back and tail. I assume that the nett induced electric field and the (small) triboelectric effect on the skin determine the charge imbalances 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 have the greatest impact on determining the size of the electric field that impacts the driver’s back and tail. Charged while driving a car (part 1)

42 Doug Mason41 Charged while driving a car (part 2) This shows that the body does not assume a significant overall charge imbalance. Maybe there is a potential gradient caused by the presence of the charge near the driver’s back and tail, with the driver’s fingers assuming an opposite potential, as the charges are driven from the field induced by the seat, and the fingers are outside that electric field. This is what I have assumed. This shows that the body does not assume a significant overall charge imbalance. Maybe there is a potential gradient caused by the presence of the charge near the driver’s back and tail, with the driver’s fingers assuming an opposite potential, as the charges are driven from the field induced by the seat, and the fingers are outside that electric field. This is what I have assumed. This would mean, as I have described, that the observed “discharge” between the person and the car body is actually a neutralisation of those charges on the fingers, and this is thus the time that the body receives an actual overall charge. This would mean, as I have described, that the observed “discharge” between the person and the car body is actually a neutralisation of those charges on the fingers, and this is thus the time that the body receives an actual overall charge.

43 Doug Mason42 Charged while driving a car (part 3) 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 have described, a charge induced on the driver’s back? 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 have described, a charge induced on the driver’s back? I need a description that can be understood by a reasonable Process Worker - no maths, no “in-terms” - just a plain English description that relies on basic concepts. I need a description that can be understood by a reasonable Process Worker - no maths, no “in-terms” - just a plain English description that relies on basic concepts. This is all relevant to the creation and management of a charge by an Electronics Assembler at their workplace. This is all relevant to the creation and management of a charge by an Electronics Assembler at their workplace.

44 Doug Mason43 I am driving my car As I drive my car, there is constant movement between my clothes and my car seat, and between my body and my clothes. As I drive my car, there is constant movement between my clothes and my car seat, and between my body and my clothes. These movements create charge imbalances on the surfaces of my clothes and my skin. These movements create charge imbalances on the surfaces of my clothes and my skin. These imbalances set up strong electric fields that affect charge distribution in my body. These imbalances set up strong electric fields that affect charge distribution in my body.

45 Doug Mason44 Charge distribution Charge imbalances (and strong electric fields) appear at the: Charge imbalances (and strong electric fields) appear at the: – outer surface of my clothes – parts of my body that are influenced by the strong electric field (opposite polarity to the source) – remote exposed parts of my body (same polarity as the source of the originating charge imbalance)

46 Doug Mason45 Further charging as I leave the car Further triboelectric activity occurs as I turn to get out of the car. Further triboelectric activity occurs as I turn to get out of the car. Also, the Voltage of the charge increases when I stand up, since my body now presents a smaller area relative to the ground. Also, the Voltage of the charge increases when I stand up, since my body now presents a smaller area relative to the ground.

47 Doug Mason46 A discharge before exiting If, before leaving the car, I touch a ready source of charges (such as the metal door handle), the charges enter my body to balance the charge imbalance on my fingers. If, before leaving the car, I touch a ready source of charges (such as the metal door handle), the charges enter my body to balance the charge imbalance on my fingers. This discharge creates an overall charge imbalance on my body. This discharge creates an overall charge imbalance on my body. This imbalance declines as the charge on my clothes decline and I continue to touch sources of ready charges while this is occurring. This imbalance declines as the charge on my clothes decline and I continue to touch sources of ready charges while this is occurring.

48 Doug Mason47 Not discharging before leaving n However, if I touch only non- conductors as I leave the car, the charge distribution continues on my body for as long as the charge imbalance remains on the outer surface of my clothing.

49 Doug Mason48 Discharging to the car body In this case, it is likely there will be a movement of charges between my body and a source of ready charges (such as the car body).

50 Doug Mason49 It’s the same at your work place If you are not provided with an ESD-safe chair at your work place, the same actions occur as with the car driver. If you are not provided with an ESD-safe chair at your work place, the same actions occur as with the car driver. Even though in most instances you do not feel the discharge as you leave your car, it is likely that one exists. Even though in most instances you do not feel the discharge as you leave your car, it is likely that one exists. The sensitivity level of many electronic components means that they can be affected by a discharge produced by the seat where you work, even though you do not feel it. The sensitivity level of many electronic components means that they can be affected by a discharge produced by the seat where you work, even though you do not feel it. The only safe way is to always wear a properly connected and functioning wrist strap. The only safe way is to always wear a properly connected and functioning wrist strap.

51 Doug Mason50 Is a smock a Faraday Cage? Thoughts and theories (3)

52 Doug Mason51 A smock as a Faraday Cage? I consistently read that an ESD smock functions as a Faraday Cage. I consistently read that an ESD smock functions as a Faraday Cage. I also read that a Faraday Cage is a hollow conductor that distributes its charge imbalance on its outer surface, a fact made use of in the shielding bag and tote box. I also read that a Faraday Cage is a hollow conductor that distributes its charge imbalance on its outer surface, a fact made use of in the shielding bag and tote box. But, I reason, if a smock holds its charges on its outer surface, surely this is bringing it close to the components and assemblies being worked on, which is not wanted. But, I reason, if a smock holds its charges on its outer surface, surely this is bringing it close to the components and assemblies being worked on, which is not wanted. Or have I missed the point, is the inside of the garment the outside of the Cage? Or have I missed the point, is the inside of the garment the outside of the Cage?

53 Doug Mason52 A hollow conductor A Faraday Cage is a hollow conductor. Michael Faraday

54 Doug Mason53 Charges sit on the outside When a Faraday Cage is placed in an electric field, the charges sit on the outside of the conductive surface, and the field does not penetrate it.

55 Doug Mason54 Two practical applications This fact is made use of in: – the static shielding bag, which has a continuous conductive layer, – the tote box, made of conductive material. If there is an opening in the conductive layer, some of the electric field may pass through it.

56 Doug Mason55 The “outside” of a Faraday Cage The “outside” surface of a Faraday Cage is the surface that is closest to the electric field.

57 Doug Mason56 A field placed inside a Faraday Cage When there is an electric field inside a Faraday Cage, the “outside” of the conductor is thus the inner surface of the Cage. An electric field inside a Faraday Cage does not penetrate it, unless the continuity of the conductive layer is broken.

58 Doug Mason57 Smock has a conductive layer An ESD smock has a continuous conductive layer. This forms a Faraday Cage around the wearer. The electric field is inside the garment. (Given the nature of material, the term “outer” could be seen as being quite arbitrary, anyway.)

59 Doug Mason58 The need for a complete layer Electric fields resulting from charge imbalances produced by the wearer do not pass through the conductive layer - unless the layer is not complete (for example - if it is unbuttoned or cuffs protrude).

60 Doug Mason59 Sources of internal fields Most movement occurs with the arms, so the sleeves carry the strongest fields. These fields are continually varying. The electric fields from clothing not covered by the Faraday Cage (such as exposed sleeve cuffs) enter the work area.

61 Doug Mason60 Garments are dissipative The high resistance of the outer layer of smocks is similar to that of dissipative mats. This controls the removal rate of any charges, whether the imbalance is outside the garment or inside it.

62 Doug Mason61 Garments are anti-static The garments are also anti-static, meaning that they resist the creation of charge imbalances. The panels are sewn with material that ensures they are electrically connected.

63 Doug Mason62 ESD Thoughts and theories ESD things I think about (Rev. 1) Do you have other ESD topics we should clarify better? ESD things I think about (Rev. 1) Do you have other ESD topics we should clarify better? Graphics I did not create are ©1999 New Vision Technologies Inc.


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