ESD知识和控制.ppt

ESD知识和控制知识和控制Examples :LightningZapping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.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”A dischargeThis movement of charges is called a discharge. 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!WHAT IS ESD? ELECTRO STATIC DISCHARGE IS DEFINED AS THE TRANSFER OF ELECTRO STATIC CHARGES BETWEEN BODIES AT DIFFERENT POTENTIAL CAUSED BY DIRECT CONTACTOR INDUCED ELECTRO STATIC FIELD. . ESD EVENTIT IS AN UNPLANNED OCCURANCE OF ELECTRO- STATIC DISCHARGE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.Moving peopleImproper groundingUnshielded cablesPoor connectionsMoving machinesLow humidity (hot and dry conditions)The most common causes of ESD are:Figure 13-14: Power Transmission SystemFigure 13-15: Grounds on IC Chips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.To avoid damaging static-sensitive devices, the following procedures will help to minimize the chances of destructive static discharges:Triboelectric generationBasic Principles (2)When two materials are in intimate contact, they share electrons which are at their surfaces.When materials are in contactThe triboelectric charge of two materials in contact. When two materials are in intimate contact, they share electrons which are at their surfaces.When materials are in contactIt is possible for electrons to be “stolen” from one material by nuclei in the other material, because they have a stronger forceWhen these materials are separated, electrons are removed from one material and are transferred to the other material.When the materials are separatedElectrons “lost”Electrons “gained”When the materials are separatedElectrons “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.The triboelectric charge when two materials placed in contact are then 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 the materials are separatedElectrons “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 materials are separatedElectrons “lost”Electrons “gained”When the surfaces are rough, this intimacy and separation is assisted by rubbing the materials together.When the materials are separatedElectrons “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 materials are separatedElectrons “lost”Electrons “gained”The drier the air (lower relative humidity, RH) the higher the generated chargeThe creation of a charge when materials are separated is termed “triboelectric charging”Charging by InductionBasic Principles Charging by inductionThe 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. Charging by inductionIf 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.Charging by inductionWalking on carpetThoughts and theories Walking across carpetWalking across a carpet creates a charge imbalance on the lower surface of shoes.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.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).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.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.An overall charge imbalanceTherefore, after that brief encounter with the metallic object, my body now has an overall charge imbalance.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.ELECTROSTATIC DISCHARGE PROCESS1. 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. 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 CHARGEð FRICTIONð SEPERATIONð INDUCTIONCAUSES FOR ESD GENERATIONF WALKING ON SYNTHETIC SURFACEF RELATIVE MOVEMENT ON CHAIRF TABLE, COMPUTER, PLASTIC PARTS NYLON OR SYNTHETIC CLOTHESF CLEANING WITH COMPRESSED AIRF CLEANING WITH SOLVENTESDFACTORS:ø TYPE OF MATERIALø RELATIVE HUMIDITYø TYPE OF CLOTHINGø SPEED AND MANNER OF WALKINGø BODY RESISTANCERECORDED ESD ACCIDENTSRECORDED ESD ACCIDENTSL In 1937, The German flying boat Hinderburg arriving in Lakehurst, New Jersey, caught fire while anchoring at its landing mast.L In 1970’s, in USA, a space craft launching rocket exploded during the fueling operation, killing 3 engineers.L 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.L 3 to 30% of Integrated Circuits manufactured every year die in “infancy” due to ESD. Device sensitivity to Electrostatic DischargeAt higher magnification the pit in the area between the base and emitter becomes more obviousDevice sensitivity to Electrostatic DischargeAt this magnification see the 1/2 ofthe width of the material has been destroyed.40 – 50% EQUIPMENTS HAVE FAILED IN THE FIELD DUE TO ESDStatisticsSENSITIVE CONSTITUENTSFAILURE MODESMOS STRUCTURESSHORTBIPOLAR JUNCTIONSLEAKAGEFILM RESISTORSVALUE SHIFTMETALIZATION STRIPESOPENFIELD PERFECT STRUCTURESOPERATIONALPIEZOELECTRIC CRYSTALSDEGRADEDCLOSELY SPACED CONDUCTORSDEGRADED• PLASTICS• CONDUCTORS• FURNITURES• VINYL FLOOR• COOLING FANS WITH PLASTIC BLADES• PRINTERS/COPIERS• PAPER• NYLON & WOOLLEN GARMENTS• COMPRESSED AIR GUNESD SOURCESMAN MADE:MAN MADE:NATURAL:• HUMAN BODY• MOVEMENT OF CLOUDS PACKING HANDLING MATERIALS: âCOMMON POLYTHENE BAGS, WRAPS,ENVELOPESâCOMMON BUBBLE PACK FOAMâCOMMON PLASTIC TRAYS, PLASTIC TOTE BOXES, VIALSTYPICAL CHARGE GENERATORSASSEMBLY, CLEANING, TEST & REPAIR AREA ITEMS: âSPRAY CLEANERSâCOMMON SOLDER SUCKERSâCOMMON SOLDER IRONSâSOLVENT BRUSHING ( SYNTHETIC BRISTLES)âCLEANING, DRYINGâTEPARATURE CHAMBERSESD VOLTAGE MEASUREMENTELECTROSTATIC VOLTAGE MEANS OF STATIC GENERATION 10% RW 40% RW 55% RWPERSON WALKING ACROSS CARPETPERSON WALKING ACROSS VINYLFLOOR WORKER AT A BENCHCERAMIC DIPS IN PLASTIC TUBE CERAMIC DIPS IN VINYL SET UP TRAYS CIRCUIT AS BUBBLE PLASTIC COVER REMOVED CIRCUIT AS PACKED IN FOAM LINED SHIPPING BOX35000 15000 750012000 5000 30006000 800 4002000 700 40011500 4000 200025000 20000 700021000 11000 5500REASONS FOR DISBELIEFESD DAMAGE : WHEN UNNOTICED? HUMAN SENSE OF FEELING OF STATIC AT 4000V MUCH MORE HIGHER THAN SENSITIVITY OF COMPONENTS; HARDLY ANY PHYSICAL DAMAGE; ESD FAILURES CONSIDERED AS GENERAL COMPONENT FAILURE; FAILURE MAY NOT BE INSTANT. (LATENT FAILURE)  GUIDE TO STATIC CONTROL MATERIALSSURFACE RESISTIVITY-OHMS PER SQUAREINSULATORMATERIALS IN THIS RANGE ARE NOT EFFECTIVE FOR STATIC CONTROL1012 To 10 151010 To 10 12ANTISTATICTHESE MATERIALS DO NOT GENERATE AND SUPPORT HIGH STATIC CHARGES. BUT DISCHARGE RATES ARE TOO SLOW FOR MOST INDUSTRIAL APPLICATIONS.SURFACE RESISTIVITY-OHMS PER SQUARE GUIDE TO STATIC CONTROL MATERIALS GUIDE TO STATIC CONTROL MATERIALSSURFACE RESISTIVITY-OHMS PER SQUARESTATIC DISSIPATORS ( PARTIALLY CONDUCTIVE)MATERIALS MOST SUITABLE FOR STATIC CONTROL WORK SURFACES, FLOORING AND FLOOR MATS, SEALING, OVERALLS106 To 10 9GUIDE TO STATIC CONTROL MATERIALSSURFACE RESISTIVITY-OHMS PER SQUARECONDUCTIVEMATERIALS FOR CONTAINERS AND HANDLING EQUIPMENT.BELOW 104 OHMS PER SQUARE EFFECTIVE STATIC SHIELDING IS POSSIBLE,OPERATOR SAFELY WILL BE COMPROMISED IF THE EARTH PATH THROUGH BENCH MATS, FLOOR MATS AND FLOORING LESS THAN 5 X 104 OHMS AND MAINS POWERED EQUIPMENT’S IN USE.101 To 10 4OBJECTIVES OF ESD CONTROLOBJECTIVES OF ESD CONTROL| PREVENTING STATIC CHARGE GENERATION|DISSIPATING THE DEVELOPED CHARGE|NEUTRALISING DEVELOPED CHARGE FOR A CHARGE FREE ZONECONTROLLING OF ESDCONTROLLING OF ESD«WORK SURFACE«AIR«HUMAN BODY«FLOORDO’Sþ MINIMISE HANDLING.þ KEEP PARTS IN ORIGINAL PACKING UNTILL READY FOR USE.þ USE ESD PROTECTIVE CONTAINERS AND BAGS.þ DISCHARGE STATIC BEFORE HANDLING DEVICE BY TOUCHING NEARBY GROUNDED SURFACE.þ HANDLE DEVICES BY THE BODY.þ TOUCH THE ESD PROTECTIVE PACKAGE BEFORE TOUCHING INSIDE OF DEVICE.þ KEEP A DUST FREE WORK AREA.DONT’Sý TOUCH THE LEADS OF DEVICE.ý SLIDE ES DEVICES OVER ANY SURFACE.ý PUT MASKING TAPE ON PROGRAMMABLE IC’S.ý STORE OR CARRY SENSITIVE COMPONENTS OR ASSEMBLIES IN PLASTIC BAGS.ý STORE SENSITIVE COMPONENTS IN THERMOCOLE/PLASTIC FOAM.ý HANDLE ES DEVICES IN “NON ESD CONTROLLED” ENVIRONMENT. ESD MODELSESD MODELS HAVE BEEN DEFINED TO DESCRIBE THE EFFECTS ON ESD SENSITIVE DEVICES:ÿ HUMAN BODY MODELÿ CHARGED DEVICE MODELÿ MACHINE MODELHuman Body Model (HBM){ The basic human body model consists of body capacitance and resistance. The charge is stored in the body capacitance and the discharge occurs through the body resistance.{ When a charged person handles or comes in close proximity to an ESD sensitive part, the part may be damaged by direct discharge or by an electro static field.<0.1mHRbVbCbCb : 50 to 350pFRb : 150 to 10KOhmsVb : 3 to 20 KV^Human Body Model (HBM)HUMAN BODY CAPACITANCE AND RESISTANCEHUMAN BODY CAPACITANCE AND RESISTANCE o50-100pF50pF100pF100pFRbo ^^TYPICAL ESD CURRENT WAVE FORMTYPICAL ESD CURRENT WAVE FORM. . . . . . . . ....................ttf=100nSectr=1nSec40AI^^Machine ModelA discharge similar to the HBM event also can occur from a charged conductive object, such as a metallic tool or fixture. . Charged Device ModelThe transfer of charge from an ESDS device is also an ESD event. A device may become charged, for example, from sliding down the feeder in an automated assembler. If it then contacts the insertion head or another conductive surface, a rapid discharge may occur from the device to the metal object. This event is known as the Charged Device Model (CDM).ESD CONTROL DEVICESESD CONTROL DEVICESF ANTISTATIC VINYL TABLE MATF CONDUCTIVE FLOOR MATF ESD LAMINATEF ESD WRIST STRAPF ESD HEEL STRAPF ESD TOE STRAPF COMMON POINT GROUNDF ANTISTATIC BINS/TRAYSF PCB STORAGE RACKF CONDUCTIVE FOAMESD AUDITMATERIALS CLASSIFICATION MATERIAL SURFACE VOLUME CLASS RESISTIVITY RESISTIVITY SHIELDING104 OR LESS102 OR LESS CONDUCTIVE105 OR LESS104 OR LESS DISSIPATIVE105 TO 1010104 TO 109 ANTISTATIC1010 TO 1012--- INSULATIVE >1015 >1014ESD AUDITÃ PERSONNEL TRAINING FOR ESD PREVENTIVEÃ AWARENESS TRAININGÃ CERTIFICATION TRAININGÃ CONTROL PROGRAM AUDITESD TEST & MEASURING INSTRUMENTSESD TEST & MEASURING INSTRUMENTSF STATIC CHARGE METERFWRIST STRAP AND GROUND TESTERFFOOTWEAR TESTERFSURFACE RESISTIVITY METERFSTATIC SENSORFCONTINUOUS WRIST STRAP MONITORFCONTINUOUS WORK STATION MONITORFTEMPARATURE AND HUMIDITY INDICATORTESTING EVALUATIONTESTING EVALUATIONThe test evaluation report consists of the following test areas for each ESD item/s:vPOINT TO POINT SURFACE RESISTIVITY TOP/BOTTOMvPOINT TO POINT SURFACE RESISTIVITY IN/OUTvSURFACE TO GROUND RESISTANCEvPERSON TO GROUND RESISTANCEvSTATIC CHARGE MEASURING TESTvSTATIC SHIELDING TEST TESTING EVALUATION W Antistatic P.E BagsW Static Shield BagsW Conductive BagsW Conductive Grid BagsW Antistatic ApronsW Conductive BrushW Foot WearW WESD Mat conductive MatW Work SurfaceW ESD LaminateW Wrist StrapW Heel StrapW ESD ChairThe tests are generally conducted for the following item/s:PERSONAL GROUNDINGTwo types of Personal Grounding:Wrist StrapsFootwearWRIST STRAPSð Daily Check with Wrist Strap Wornð Test with a Wrist Strap testerFloorð Point to PointFloorð Resistance to GroundGarmentsð Point to PointGarmentsð Point to Groundð May need person wearing garmentNeeds to be connected to ground as wor nChairð Check all parts of Chairs to Groundð Seat, Backrest, Armrest, Foot RestTYPES OF ESD DAMAGECATASTROPHIC FAILUREßUPSET FAILURESHIELDINGFARADAY CAGETypes of Faraday Cages•Metallized & Conductive Shielding Bags•Conductive tote box with coverA hollow conductorA Faraday Cage is a hollow conductor.Michael FaradayWORK STATIONElectrostatic Voltmeter (ESV)Measurement of Static ElectricityStatic electricity is measured in coulombs. The charge "q" on an object is determined by the product of the capacitance of the object "C" and the voltage potential on the object (V):q=CVCommonly, however, we speak of the electrostatic potential on an object, which is expressed as voltage.ESD Damage-How Devices Fail­Electrostatic damage to electronic devices can occur at any point from manufacture to field service. ­Damage results from handling the devices in uncontrolled surroundings or when poor ESD control practices are used. ­Generally damage is classified as either a catastrophic failure or a latent defect.。