ESD知识和控制ppt课件

1、An extensive course onExamples :LightningZappingAn atom is made up of chargesnAn atom is made up of charges.nIn 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.nThe el

2、ectrons whirl around the centre like planets.Creating a charge imbalancenWhen an atom loses an electron, it has a charge imbalance.nSince this atom has lost an electron, which is a negative charge, the atom is now a positive charge.nWhen it gains an extra electron, an atom becomes a negative charge.

3、Electron “lost”A dischargenThis movement of charges is called a discharge.This powerful, rapid movement of charges can damage electronic components.Lets see it again!IT IS AN UNPLANNED OCCURANCE OF ELECTRO- STATIC DISCHARGEMoving peopleImproper groundingUnshielded cablesPoor connectionsMoving machin

4、esLow humidity (hot and dry conditions)The most common causes of ESD are:Figure 13-14: Power Transmission SystemFigure 13-15: Grounds on IC ChipsSome 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

5、 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 tw

6、o materials are in intimate contact, they share electrons which are at their surfaces.When materials are in contactThe 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 pos

7、sible for electrons to be “stolen” from one material by nuclei in the other material, because they have a stronger forceWhen these materials are separated, electrons are removed from one material and are transferred to the other material.When the materials are separatedElectrons “lost”Electrons “gai

8、ned”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 contac

9、t. 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.W

10、hen 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

11、 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 materialsWhen the materials are separated

12、Electrons “lost”Electrons “gained”The drier the air (lower relative humidity, RH) the higher the generated chargeThe creation of a charge when materials are separated is termed “triboelectric charging”Charging by InductionBasic Principles Charging by inductionCharging by inductionCharging by inducti

13、onWalking on carpetThoughts and theories Walking across carpetnWalking across a carpet creates a charge imbalance on the lower surface of shoes.A strong electric fieldnThis charge imbalance creates a strong electric field that emanates in all directions.nThe material in the sole of shoe enables a st

14、rong field to influence charges within foot.An induced chargenSince 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.nBut the body still has a balanced charge overall (it has not lost or gained any charg

15、es).Contacting a source of chargesnWhile 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.)nThis enables charges to be provided by the metallic object.Charging through the

16、airnThis movement of charges is thus producing an overall charge imbalance in my body, since I was previously neutral overall.An overall charge imbalancenTherefore, after that brief encounter with the metallic object, my body now has an overall charge imbalance.Removing that chargenThe only way to r

17、emove the possibility of damaging an ESD-sensitive device or assembly is to remove the overall charge imbalance on my body.nThis 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.1. Ch

18、arge 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 thro

19、ugh the capacitance between the object and ground. 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 FRICTION SEPERATION INDUCTIONF WALKING ON SYNTHETIC SURF

20、ACEF RELATIVE MOVEMENT ON CHAIRF TABLE, COMPUTER, PLASTIC PARTS NYLON OR SYNTHETIC CLOTHESF CLEANING WITH COMPRESSED AIRF CLEANING WITH SOLVENTL In 1937, The German flying boat Hinderburg arriving in Lakehurst, New Jersey, caught fire while anchoring at its landing mast.L In 1970s, in USA, a space c

21、raft 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

22、 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 obviousDevice sensitivity to Electrostat

23、ic DischargeAt this magnification see the 1/2 ofthe width of the material has been destroyed.StatisticsSENSITIVE CONSTITUENTSFAILURE MODESMOS STRUCTURESSHORTBIPOLAR JUNCTIONSLEAKAGEFILM RESISTORSVALUE SHIFTMETALIZATION STRIPESOPENFIELD PERFECT STRUCTURESOPERATIONALPIEZOELECTRIC CRYSTALSDEGRADEDCLOSE

24、LY SPACED CONDUCTORSDEGRADED PLASTICS CONDUCTORS FURNITURES VINYL FLOOR COOLING FANS WITH PLASTIC BLADES PRINTERS/COPIERS PAPER NYLON & WOOLLEN GARMENTS COMPRESSED AIR GUN HUMAN BODY MOVEMENT OF CLOUDS PACKING HANDLING MATERIALS: C O M M O N P O L Y T H E N E B A G S , WRAPS,ENVELOPESCOMMON BUBBLE P

25、ACK FOAMCOMMON PLASTIC TRAYS, PLASTIC TOTE BOXES, VIALSASSEMBLY, CLEANING, TEST & REPAIR AREA ITEMS: SPRAY CLEANERSCOMMON SOLDER SUCKERSCOMMON SOLDER IRONSSOLVENT BRUSHING ( SYNTHETIC BRISTLES)CLEANING, DRYINGTEPARATURE CHAMBERSESD VOLTAGE MEASUREMENTELECTROSTATIC VOLTAGE MEANS OF STATIC GENERATION

26、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 40

27、011500 4000 200025000 20000 700021000 11000 5500REASONS 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. (

28、LATENT FAILURE) SURFACE RESISTIVITY-OHMS PER SQUAREINSULATORMATERIALS IN THIS RANGE ARE NOT EFFECTIVE FOR STATIC CONTROL1012 To 10 151010 To 10 12ANTISTATICTHESE MATERIALS DO NOT GENERATE AND SUPPORT HIGH STATIC CHARGES. BUT DISCHARGE RATES ARE TOO SLOW FOR MOST INDUSTRIAL APPLICATIONS.SURFACE RESIS

29、TIVITY-OHMS PER SQUARESURFACE RESISTIVITY-OHMS PER SQUARESTATIC DISSIPATORS ( PARTIALLY CONDUCTIVE)MATERIALS MOST SUITABLE FOR STATIC CONTROL WORK SURFACES, FLOORING AND FLOOR MATS, SEALING, OVERALLS106 To 10 9SURFACE RESISTIVITY-OHMS PER SQUARECONDUCTIVEMATERIALS FOR CONTAINERS AND HANDLING EQUIPME

30、NT.BELOW 104 OHMS PER SQUARE E F F E C T I V E S T A T I C S H I E L D I N G I S P O S S I B L E , O P E R ATO R S A F E LY W I L L B E COMPROMISED IF THE EARTH PATH THROUGH BENCH MATS, FLOOR MATS AND FLOORING LESS THAN 5 X 104 OHMS AND MAINS POWERED EQUIPMENTS IN USE.101 To 10 4| PREVENTING STATIC

31、CHARGE GENERATION|DISSIPATING THE DEVELOPED CHARGE|NEUTRALISING DEVELOPED CHARGE FOR A CHARGE | FREE ZONEWORK SURFACEAIRHUMAN BODYFLOORDOS MINIMISE HANDLING. KEEP PARTS IN ORIGINAL PACKING UNTILL READY FOR USE. USE ESD PROTECTIVE CONTAINERS AND BAGS. DISCHARGE STATIC BEFORE HANDLING DEVICE BY TOUCHI

32、NG NEARBY GROUNDED SURFACE. HANDLE DEVICES BY THE BODY. TOUCH THE ESD PROTECTIVE PACKAGE BEFORE TOUCHING INSIDE OF DEVICE. KEEP A DUST FREE WORK AREA. TOUCH THE LEADS OF DEVICE. SLIDE ES DEVICES OVER ANY SURFACE. PUT MASKING TAPE ON PROGRAMMABLE ICS. STORE OR CARRY SENSITIVE COMPONENTS OR ASSEMBLIES

33、 IN PLASTIC BAGS. S T O R E S E N S I T I V E C O M P O N E N T S I N THERMOCOLE/PLASTIC FOAM. HANDLE ES DEVICES IN “NON ESD CONTROLLED” ENVIRONMENT. ESD MODELSESD MODELS HAVE BEEN DEFINED TO DESCRIBE THE EFFECTS ON ESD SENSITIVE DEVICES: HUMAN BODY MODEL CHARGED DEVICE MODEL MACHINE MODEL The basic

34、 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 e

35、lectro static field.1015 1014 PERSONNEL TRAINING FOR ESD PREVENTIVE AWARENESS TRAINING CERTIFICATION TRAINING CONTROL PROGRAM AUDITF STATIC CHARGE METERFWRIST STRAP AND GROUND TESTERFFOOTWEAR TESTERFSURFACE RESISTIVITY METERFSTATIC SENSORFCONTINUOUS WRIST STRAP MONITORFCONTINUOUS WORK STATION MONITO

36、RFTEMPARATURE AND HUMIDITY INDICATORThe 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 TESTvSTATI

37、C SHIELDING TEST Antistatic P.E Bags Static Shield Bags Conductive Bags Conductive Grid Bags Antistatic Aprons Conductive Brush Foot WearW WESD MatW 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 StrapsFootwe