1. ESD Thoughts and theories
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.
(c) 2000 Doug Mason

2. Introduction
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.
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.
(c) 2000 Doug Mason

3. Introduction
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.
When such people understand the reasons they need to take such steps, this should surely help them implement the required strategies.
(c) 2000 Doug Mason

4. Introduction
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)
If you can make a useful contribution to my knowledge, please do so. My address is
Many thanks,
Doug
(c) 2000 Doug Mason

5. First, some basic principles . . .
(c) 2000 Doug Mason

6. Atomic Theory Basic Principles (1) dmason@alphalink.com.au
(c) 2000 Doug Mason

7. 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.
(c) 2000 Doug Mason

8. Creating a charge imbalance
Electron “lost”
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.
(c) 2000 Doug Mason

9. A discharge Let’s see it again!
This powerful, rapid movement of charges can damage electronic components.
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.
Let’s see it again!
This movement of charges is called a discharge.
(c) 2000 Doug Mason

10. Triboelectric generation
Basic Principles (2)
(c) 2000 Doug Mason

11. When materials are in contact
(c) 2000 Doug Mason

12. When materials are in contact
(c) 2000 Doug Mason

13. When materials are in contact
When two materials are in intimate contact, they share electrons which are at their surfaces.
(c) 2000 Doug Mason

14. When materials are in contact
It is possible for electrons to be “stolen” from one material by nuclei in the other material, because they have a stronger force
When two materials are in intimate contact, they share electrons which are at their surfaces.
(c) 2000 Doug Mason

15. 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.
It is possible for electrons to be “stolen” from one material by nuclei in the other material, because they have a stronger force
(c) 2000 Doug Mason

16. When the materials are separated
(c) 2000 Doug Mason

17. 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.
(c) 2000 Doug Mason

18. When the materials are separated
Electrons “lost”
Electrons “gained”
This action takes place with all types of materials. With insulators, the charges remain at the points of contact. A charge spreads all over an ungrounded conductor.
When these materials are separated, electrons are removed from one material and are transferred to the other material.
(c) 2000 Doug Mason

19. When the materials are separated
Electrons “lost”
Electrons “gained”
This action takes place with all types of materials. With insulators, the charges remain at the points of contact. A charge spreads all over an ungrounded conductor.
The loss and gain of these electrons creates an imbalance of negative and positive charges on the surface of each material.
(c) 2000 Doug Mason

20. 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.
When the surfaces are rough, this intimacy and separation is assisted by rubbing the materials together.
(c) 2000 Doug Mason

21. 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.
When the surfaces are rough, this intimacy and separation is assisted by rubbing the materials together.
(c) 2000 Doug Mason

22. 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.
The drier the air (lower relative humidity, RH) the higher the generated charge.
(c) 2000 Doug Mason

23. When the materials are separated
Electrons “lost”
Electrons “gained”
The drier the air (lower relative humidity, RH) the higher the generated charge.
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).
(c) 2000 Doug Mason

24. The creation of a charge when materials are separated is termed “triboelectric charging”
(c) 2000 Doug Mason

25. Charging by Induction Basic Principles (3) dmason@alphalink.com.au
(c) 2000 Doug Mason

26. Charging by induction
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.
(c) 2000 Doug Mason

27. The charge imbalance on a surface produces an electric field.
Charging by induction
The charge imbalance on a surface produces an electric field.
The presence of this very strong force causes similar charges on the surfaces of nearby conductors to be repelled.
(c) 2000 Doug Mason

28. 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.
(c) 2000 Doug Mason

29. 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.
(c) 2000 Doug Mason

30. Thoughts and theories (1)
Walking on carpet
Thoughts and theories (1)
(c) 2000 Doug Mason

31. 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?”
My current theory is described in the next few slides.
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.
(c) 2000 Doug Mason

32. Walking across carpet
Walking across a carpet creates a charge imbalance on the lower surface of my shoes.
(c) 2000 Doug Mason

33. 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.
(c) 2000 Doug Mason

34. 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).
(c) 2000 Doug Mason

35. 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.
(c) 2000 Doug Mason

36. Charging through the air
If the charge imbalance on my body is large enough, I do not need to touch the object, as the imbalance could allow a movement of charges through the air.
This movement of charges is thus producing an overall charge imbalance in my body, since I was previously neutral overall.
(c) 2000 Doug Mason

37. An overall charge imbalance
Therefore, after that brief encounter with the metallic object, my body now has an overall charge imbalance.
(c) 2000 Doug Mason

38. 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.
(c) 2000 Doug Mason

39. Thoughts and theories (2)
Driving a car
Thoughts and theories (2)
(c) 2000 Doug Mason

40. Charged while driving a car (part 1)
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.
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.
(c) 2000 Doug Mason

41. 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 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.
(c) 2000 Doug Mason

42. 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?
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.
(c) 2000 Doug Mason

43. 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.
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.
(c) 2000 Doug Mason

44. Charge distribution
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)
(c) 2000 Doug Mason

45. Further charging as I leave 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.
(c) 2000 Doug Mason

46. 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.
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.
(c) 2000 Doug Mason

47. Not discharging before leaving
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.
(c) 2000 Doug Mason

48. 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).
(c) 2000 Doug Mason

49. 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.
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 only safe way is to always wear a properly connected and functioning wrist strap.
(c) 2000 Doug Mason

50. Is a smock a Faraday Cage?
Thoughts and theories (3)
(c) 2000 Doug Mason

51. A smock 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.
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?
(c) 2000 Doug Mason

52. A hollow conductor A Faraday Cage is a hollow conductor.
Michael Faraday
(c) 2000 Doug Mason

53. 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.
(c) 2000 Doug Mason

54. 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.
(c) 2000 Doug Mason

55. The “outside” of a Faraday Cage
The “outside” surface of a Faraday Cage is the surface that is closest to the electric field.
(c) 2000 Doug Mason

56. 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.
(c) 2000 Doug Mason

57. 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.)
(c) 2000 Doug Mason

58. 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).
(c) 2000 Doug Mason

59. 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.
(c) 2000 Doug Mason

60. 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.
(c) 2000 Doug Mason

61. 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.
(c) 2000 Doug Mason

62. ESD Thoughts and theories
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.
(c) 2000 Doug Mason