Advanced-PCB-design-and-layout-for-EMC---Part-7

AdvancedPCBDesignandLayoutforEMCPart7Routingandlayerstacking,includingmicroviatechnologyByKeithArmstrongC.EngMIEEMIEEEThisistheseventhinaseriesofeightarticlesongood-practicedesigntechniquesforelectromagneticcompatibility(EMC)forprintedcircuitboard(PCB)designandlayout.ThisseriesisintendedforthedesignersofanyelectroniccircuitsthataretobeconstructedonPCBs,andofcourseforthePCBdesignersthemselves.Allapplicationsareasarecovered,fromhouseholdappliances;commercial,medicalandindustrialequipment;throughautomotive,railandmarinetoaerospaceandmilitary.ThesePCBtechniquesarehelpfulwhenitisdesiredto…•Savecostbyreducing(oreliminating)enclosure-levelshielding•Reducetime-to-marketandcompliancecostsbyreducingthenumberofdesigniterations•Improvetherangeofco-locatedwirelessdatacomms(GSM,DECT,Bluetooth,IEEE802.11,etc.)•Useveryhigh-speeddevices,orhighpowerdigitalsignalprocessing(DSP)•UsethelatestICtechnologies(130nmor90nmchipprocesses,’chipscale’packages,etc.)Thetopicstobecoveredinthisseriesare:1.Savingtimeandcostoverall2.Segregationandinterfacesuppression3.PCB-chassisbonding4.Referenceplanesfor0Vandpower5.Decoupling,includingburiedcapacitancetechnology6.Transmissionlines7.Routingandlayerstacking,includingmicroviatechnology8.AnumberofmiscellaneousfinalissuesApreviousseriesbythesameauthorintheEMC&ComplianceJournalin1999DesignTechniquesforEMC[1]includedasectiononPCBdesignandlayout(Part5-PCBDesignandLayout,October1999,pages5-17),butonlysetouttocoverthemostbasicPCBtechniquesforEMC-theonesthatallPCBsshouldfollownomatterhowsimpletheircircuits.Thatseriesispostedonthewebandthewebversionshavebeensubstantiallyimprovedovertheinterveningyears[2].Otherarticlesandpublicationsbythisauthor(e.g.[3][4]andVolume3of[5])havealsoaddressedbasicPCBtechniquesforEMC.Liketheabovearticles,thisserieswillnotspendmuchtimeanalysingwhythesetechniqueswork,itwillfocusondescribingtheirpracticalapplicationsandwhentheyareappropriate.Butthesetechniquesarewell-proveninpracticebynumerousdesignersworld-wide,andthereasonswhytheyworkareunderstoodbyacademics,sotheycanbeusedwithconfidence.Therearefewtechniquesdescribedinthisseriesthatarerelativelyunproven,andthiswillbementionedwhereappropriate.TableofContents,forthisPartoftheseries1Routingandlayerstackingtechniques,andmicroviatechnology2Routing3Stack-ups3.1Thebenefitsofclosertrace-planespacing3.2Thebenefitsofclosercomponent-planespacing3.3Copperbalancing3.4Single-layerPCBs3.5Two-layerPCBs3.6Four-layerPCBstack-ups3.7SixlayerPCBs3.8EightlayerPCBs3.9PCBswithmorethaneightlayers3.10NumberofPCBlayersandcost-effectivedesigninreal-life4EMCissueswithcopperbalancingusingareafillsorcross-hatches5HDIPCBtechnology5.1WhatisHDI?5.2TheEMCbenefitsofHDI5.3HDIsuppliersandcosts5.4HDIPCDdesignissues5.5MoreinformationonHDI6Currentcapacityoftraces6.1Handlingsurgeandtransientcurrents6.2Maximumcontinuousd.c.andlowfrequencycurrenthandling6.3VoltagedropsinthePCB’spowerdistribution6.4HandlingcontinuousRFcurrents6.5Anoteonaccuracy7Transientandsurgevoltagecapacityoflayouts7.1Trace-traceandtrace-metalspacing7.2TheEMCandsafetyproblemscausedbycompliancewiththeRoHSdirective8EMC-competentQA,changecontrol,cost-reduction9Compromises10References11SomeusefulsourcesoffurtherinformationonPCBtransmissionlines1Routingandlayerstackingtechniques,andmicroviatechnologyThispartoftheseriesisconcernedwiththebusinessofroutingthetracesonthePCBartwork,etchingandplatingthecopperfoils,laminatingtheetchedfoilswithlayersofdielectric,anddrillingandplatingtheviaholes.AllofthesecanhaveaneffectonaPCB’sEMC.Someoftherelevantissueshavealreadybeendiscussedinpreviouspartsofthisseries,inwhichcasetheywillonlybebrieflymentionedhere,withareferencetotheearlierpart.Ifyouhavemissedanypartsofthisseries,youcandownloadthemfromthearchiveat://://’sarchives.2RoutingPreviouspartsofthisserieshavedescribedanumberofPCBcomponentplacementandroutingtechniques,forexample-a)Part2[6]discussesthesegregation(partitioning)ofcomponentsandtheirassociatedtracesintodifferentzones,andhowtoroutethetracesthatmustinterconnectthezones.Italsocoverscomponentplacementandtraceroutinginfilterzones,andwhenshieldingcansareusedonthePCB.b)Part4[7]discussesthedesignofplanes,andtheroutingoftraceswithrespecttoplaneedges,andalsowithrespecttoanysplitsorgapsinaplane.c)Part5[8]discussesroutingtechniquesfordecouplingcapacitors(decaps).d)Part6[9]discussesroutingtechniquesfortracesthatcarryhigh-speedorhigh-frequencysignalsornoises-especiallyitssection3.1andfigures6T-6W.Itcontainsalotaboutcontrollingtracecharacteristicimpedanceandpropagationvelocity,andwhentransmissionlinetechniquesarenotrequiredthismaybeignored.ButnotethatforgoodPCBEMCperformance,transmissionlinetechniquesareincreasinglyrequired