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1、HibbelerR.C.“Force-SystemResultantsandEquilibrium”ThermalDesignofElectronicEquipment.Ed.RalphRemsburgBocaRaton:CRCPressLLC,20010082-01Page1Wednesday,August23,20009:51AM1IntroductiontoThermalDesignofElectronicEquipment1.1INTRODUCTIONTOTHEMODESOFHEATTRANSFERINELECTR
2、ONICEQUIPMENTElectronicdevicesproduceheatasaby-productofnormaloperation.Whenelectricalcurrentflowsthroughasemiconductororapassivedevice,aportionofthepowerisdissipatedasheatenergy.Besidesthedamagethatexcessheatcancause,italsoincreasesthemovementoffreeelectronsinasem
3、iconductor,whichcancauseanincreaseinsignalnoise.Theprimaryfocusofthisbookistoexaminevariouswaystoreducethetemperatureofasemiconductor,orgroupofsemiconductors.Ifwedonotallowtheheattodissipate,thedevicejunctiontemperaturewillexceedthemaximumsafeoperatingtemperatures
4、pecifiedbythemanufacturer.Whenadeviceexceedsthespecifiedtemperature,semiconductorperformance,life,andreliabilityaretremendouslyreduced,asshowninFigure1.1.Thebasicobjective,then,istoholdthejunctiontemperaturebelowthemaximumtemperaturespecifiedbythesemiconductormanufac
5、turer.Naturetransfersheatinthreeways,convection,conduction,andradiation.Wewillexploretheseingreaterdetailinsubsequentchapters,butasimpledefinitionofeachisappropriateatthisstage.1.1.1CONVECTIONConvectionisacombinationofthebulktransportationandmixingofmacroscopicpart
6、sofhotandcoldfluidelements,heatconductionwithinthecoolantmedia,andenergystorage.Convectioncanbeduetotheexpansionofthecoolantmediaincontactwiththedevice.Thisiscalledfreeconvection,ornaturalconvection.Con-vectioncanalsobeduetootherforces,suchasafanorpumpforcingthecoo
7、lantmediaintomotion.Thebasicrelationshipofconvectionfromahotobjecttoafluidcoolantpresumesalineardependenceonthetemperaturerisealongthesurfaceofthesolid,knownasNewtoniancooling.Therefore:qchcAs()TsTm©2001byCRCPRESSLLC0082-01Page2Wednesday,August23,20009:51AM6.05.0
8、h4.06PAL3.0FailureRateper102.0DRAM1.0Microprocessor0.02030405060708090100110120oJunctionTemperature,CFIGURE1.1ComponentfailurerateswithtemperatureforPro