Advanced-PCB-design-and-layout-for-EMC---part-1

AdvancedPCBdesignandlayoutforEMC.Part1–SavingtimeandcostoverallByEurIngKeithArmstrongC.EngMIEEMIEEE,CherryCloughConsultantsThisisthefirstinaseriesofeightarticlesongood-practiceEMCdesigntechniquesforprintedcircuitboard(PCB)designandlayout.ThisseriesisintendedforthedesignersofanyelectroniccircuitsthataretobeconstructedonPCBs,andofcourseforthePCBdesignersthemselves.Allapplicationsareasarecovered,fromhouseholdappliances,commercialandindustrialequipment,throughautomotivetoaerospaceandmilitary.ThesePCBtechniquesarehelpfulwhenitisdesiredto…•Savecostbyreducing(oreliminating)enclosure-levelshielding•Reducetimetomarketandcompliancecostsbyreducingthenumberofdesigniterations•Improvetherangeofco-locatedwirelessdatacomms(GSM,DECT,Bluetooth,IEEE802.11,etc.)•Useveryhigh-speeddevices,orhighpowerdigitalsignalprocessing(DSP)•UsethelatestICtechnologies(130nmor90nmprocesses,‘chipscale’packages,etc.)Thetopicstobecoveredinthisseriesare:1.Savingtimeandcostoverall2.Segregationandinterfacesuppression3.PCB-chassisbonding4.Referenceplanesfor0Vandpower5.Decoupling,includingburiedcapacitancetechnology6.Transmissionlines7.Routingandlayerstacking,includingmicroviatechnology8.AnumberofmiscellaneousfinalissuesApreviousseriesbythesameauthorintheEMC&ComplianceJournalin1999“DesignTechniquesforEMC”includedasectiononPCBdesignandlayout[1],butonlysetouttocoverthemostbasicPCBtechniquesforEMC–theonesthatallPCBsshouldfollownomatterhowsimpletheircircuits.Thisseriesispostedonthewebandthewebversionshavebeensubstantiallyimprovedovertheinterveningyears[2].Otherarticlesbythisauthor(e.g.[3][4])havealsoaddressedbasicPCBtechniquesforEMC.Thisserieswillnotrepeatthebasicdesigninformationinthesearticles–itwillbuilduponit.Liketheabovearticles,thisserieswillnotbotherwithwhythesetechniqueswork,theywillsimplydescribethetechniquesandwhentheyareappropriate.Butthesetechniquesarewell-proveninpracticebynumerousdesignersworld-wide,andthereasonswhytheyworkareunderstoodbyacademics,sotheycanbeusedwithconfidence.Therearefewtechniquesdescribedinthisseriesthatarerelativelyunproven,andthiswillbementionedwhereappropriate.Tableofcontentsforthispart1ReasonsforusingtheseEMCtechniques1.1Development–reducingcostsandgettingtomarketontime1.2Reducingunitmanufacturingcosts1.3Enablingwirelessdatacommunications1.4EnablingtheuseofthelatestICsandICpackages1.5Easiercomplianceforhigh-powerDSP1.6Improvingtheimmunityofanaloguecircuits2Whatdowemeanby“highspeed”3Electronictrends,andtheirimplicationsforPCBs3.1Shrinkingsilicon3.2Shrinkingpackaging3.3Shrinkingsupplyvoltages3.4PCBsarebecomingasimportantashardwareandsoftware3.5EMCtestingtrends4Designingtoreduceprojectrisk4.1Guidelines,mathsformulae,andfieldsolvers4.2Virtualdesign4.3Experimentalverification5References1ReasonsforusingtheseEMCtechniquesMostprofessionalcircuitandPCBdesignerswouldlovetoemployallofthegoodEMCtechniquesdescribedin[1]-[4]andthisseries,butareoftenpreventedfromdoingsobyprojectmanagersandothermanagerswhoonlyseethesetechniquesaswastedtimeandaddedcost.SometimesitisthemanagerofthePCBlayoutdepartmentwhopreventstheuseofgoodEMCtechniques,usuallyclaimingthattheproductcost-to-makewillincrease,butoftenreallybecausetheyhavebecomefamiliarwiththeirexistingPCBdesignrulesandbare-boardmanufacturersanddon’twanttomaketheefforttochange.Thissectionwillshowthatsuchmanagementapproachesarecompletelytheoppositeofwhatisreallyrequiredthesedaysforsuccessinthedesignandmanufactureofelectronicproductsofanytype,inanyvolume.PCBshavecontinuallybeengettingmorehigh-techandcostlyeversincetheywerefirstinvented,andtheywillcontinuealongthispathforever.InafewyearstimemicroviaPCBswithmorethan8layersandembeddedcapacitancewillbethenorm.Itisatoughcommercialworldforeveryonethesedays,andcompaniesthatdon’tkeepupwithPCBtechnologywillbeleftinthedustofthosethatdo.1.1Development–reducingcostsandgettingtomarketontimeEvenifaPCBhasnonearbywirelessdatacommunicationsantennas,andevenifitdoesnotusehigh-speeddevicesorsignals,thesePCBtechniquescansavetimeandmoneybyreducingthenumberofiterationsittakestogetthecircuitworkingwithitsfullperformancespecification.ThisisbecausemanyEMCtechniquesarealsosignalintegritytechniques.Infact,goodPCBdesignforEMCgoesbeyondtherequirementsforsignalintegrity;soaPCBthatisdesignedusinggoodEMCtechniquesgenerallyhasexcellentsignalintegrity.TheauthororiginallydevelopedthePCBdesigntechniquesdescribedin[1]-[4]overtenyearsandthreecompaniesinthe1980stoenablepowerfuldigitalprocessing,sensitivehigh-specificationanaloguecircuits,andswitch-modepowerconverterstosharethesameenclosure,eventhesamePCB,withoutcompromisingtheanalogueperformanceatall.Projectsthatusedtorequire10ormoredesigniterationscouldusethesetechniquestomeettheirperformancespecificationsonthefirstPCBprototype.Duringthe1990sitwasfoundthatthesetechniquesalsoachievedexcellentcompliancewithEMCDirectiveteststandards,withoutrequiringhigh-specificationenclosureshielding,sometimeswithoutanyshieldingatall.GoodEMCdesigntechniquesaregoodsignalintegritytechniques,forbothanalogueanddigitalcircuits.Thismeansmorepredictableproj