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ELECTRO STATIC DISCHARGE AWARENESS AND CONTROL

An extensive course on. ELECTRO STATIC DISCHARGE AWARENESS AND CONTROL. Examples : Lightning Zapping. An atom is made up of charges. An atom is made up of charges.

JasminFlorian
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ELECTRO STATIC DISCHARGE AWARENESS AND CONTROL

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  1. An extensive course on ELECTRO STATIC DISCHARGE AWARENESS AND CONTROL

  2. Examples : Lightning Zapping

  3. 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.

  4. Electron “lost” 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.

  5. 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. This powerful, rapid movement of charges can damage electronic components. • This movement of charges is called a discharge. Let’s see it again!

  6. WHAT IS ESD? ELECTRO STATIC DISCHARGE IS DEFINED AS THE TRANSFER OF ELECTRO STATIC CHARGES BETWEEN BODIES AT DIFFERENT POTENTIAL CAUSED BY DIRECT CONTACT OR INDUCED ELECTRO STATIC FIELD. ESD EVENT IT IS AN UNPLANNED OCCURANCE OF ELECTRO- STATIC DISCHARGE

  7. What is ESD—Electrostatic Discharges (ESD) are the most severe form of Electromagnet Interference (EMI). The human body can build up static charges that range up to 25,000 volts. These build-ups can discharge very rapidly into a electrically grounded body, or device. Placing a 25,000-volt surge through any electronic device is potentially damaging to it.

  8. The most common causes of ESD are: Moving people Improper grounding Unshielded cables Poor connections Moving machines Low humidity (hot and dry conditions)

  9. Figure 13-14: Power Transmission System

  10. Figure 13-15: Grounds on IC Chips

  11. To avoid damaging static-sensitive devices, the following procedures will help to minimize the chances of destructive static discharges: Some devices used to remove solder from circuit boards and chips can cause high static discharges that may damage the good devices on the board. The device in question is referred to as a solder-sucker, and is available in antistatic versions for use with MOS devices.

  12. Triboelectric generation Basic Principles (2)

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

  14. The triboelectric charge of two materials in contact.

  15. 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.

  16. Electrons “lost” Electrons “gained” When the materials are separated When these materials are separated, electrons are removed from one material and are transferred to the other material.

  17. Electrons “lost” Electrons “gained” When the materials are separated 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.

  18. The triboelectric charge when two materials placed in contact are then separated.

  19. Electrons “lost” Electrons “gained” When the materials are separated 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.

  20. Electrons “lost” Electrons “gained” When the materials are separated When the surfaces are rough, this intimacy and separation is assisted by rubbing the materials together.

  21. Electrons “lost” Electrons “gained” When the materials are separated 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

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

  23. The creation of a charge when materials are separated is termed “triboelectric charging”

  24. Charging by Induction Basic Principles

  25. 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.

  26. 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.

  27. Charging by induction

  28. Walking on carpet Thoughts and theories

  29. Walking across carpet • Walking across a carpet creates a charge imbalance on the lower surface of shoes.

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

  31. An induced charge • Since the 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 the body still has a balanced charge overall (it has not lost or gained any charges).

  32. Contacting a source of charges • While you are still on the carpet (still influenced by the electric field on the sole of your shoe),you briefly touch a metallic object (a chair, table, door knob, metal stapler, etc.) • This enables charges to be provided by the metallic object.

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

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

  35. 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.

  36. ELECTROSTATIC DISCHARGE PROCESS 1. Charge is generated on the surface of an insulator. 2. This charge is transfered to a conductor by contact or induction. 3. The charged conductor comes near a metal object (grounded or ungrounded) and a discharge occurs. 4. When a discharge occurs to an ungrounded object, the discharge current flows through the capacitance between the object and ground.

  37. STATIC GENERATION THE STATIC CHARGE IS GENERATED BY IMBALANCE IN THE MOLECULAR STRUCTURE BY RUBBING; CAUSING STRIPPING OF NEGATIVELYCHARGED ELECTRONS WITH ONE MATERIAL GETTING PASITIVE CHARGE AND OTHER NEGATIVE CAUSE FOR STATIC CHARGE • FRICTION • SEPERATION • INDUCTION

  38. CAUSES FOR ESD GENERATION ESD • WALKING ON SYNTHETIC SURFACE • RELATIVE MOVEMENT ON CHAIR • TABLE, COMPUTER, PLASTIC PARTS NYLON OR SYNTHETIC CLOTHES • CLEANING WITH COMPRESSED AIR • CLEANING WITH SOLVENT

  39. FACTORS: • TYPE OF MATERIAL • RELATIVE HUMIDITY • TYPE OF CLOTHING • SPEED AND MANNER OF WALKING • BODY RESISTANCE

  40. RECORDED ESD ACCIDENTS • In 1937, The German flying boat Hinderburg arriving in Lakehurst, New Jersey, caught fire while anchoring at its landing mast. • In 1970’s, in USA, a space craft launching rocket exploded during the fueling operation, killing 3 engineers. • In January, 1985, during the assembly of a missile in Germany, the motor case made of Kelvar, got rubbbed against the cushioning in its container. The ESD generated caused the highly flammable propellant to catch fire and the motor exploded, killing 3 people. • 3 to 30% of Integrated Circuits manufactured every year die in “infancy” due to ESD.

  41. Device sensitivity to Electrostatic Discharge At higher magnification the pit in the area between the base and emitter becomes more obvious

  42. Device sensitivity to Electrostatic Discharge At this magnification see the 1/2 of the width of the material has been destroyed.

  43. Statistics 40 – 50% EQUIPMENTS HAVE FAILED IN THE FIELD DUE TO ESD

  44. SENSITIVE CONSTITUENTS FAILURE MODES MOS STRUCTURES SHORT BIPOLAR JUNCTIONS LEAKAGE FILM RESISTORS VALUE SHIFT METALIZATION STRIPES OPEN FIELD PERFECT STRUCTURES OPERATIONAL PIEZOELECTRIC CRYSTALS DEGRADED CLOSELY SPACED CONDUCTORS DEGRADED

  45. ESD SOURCES MAN MADE: • PLASTICS • CONDUCTORS • FURNITURES • VINYL FLOOR • COOLING FANS WITH PLASTIC BLADES • PRINTERS/COPIERS • PAPER • NYLON & WOOLLEN GARMENTS • COMPRESSED AIR GUN

  46. NATURAL: • HUMAN BODY • MOVEMENT OF CLOUDS

  47. TYPICAL CHARGE GENERATORS • PACKING HANDLING MATERIALS: • COMMON POLYTHENE BAGS, WRAPS,ENVELOPES • COMMON BUBBLE PACK FOAM • COMMON PLASTIC TRAYS, PLASTIC TOTE BOXES, VIALS • ASSEMBLY, CLEANING, TEST & REPAIR AREA ITEMS: • SPRAY CLEANERS • COMMON SOLDER SUCKERS • COMMON SOLDER IRONS • SOLVENT BRUSHING ( SYNTHETIC BRISTLES) • CLEANING, DRYING • TEPARATURE CHAMBERS

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