Introduction to PCB Layout, Soldering and Construc.doc
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Introduction to PCB Layout, Soldering and Construc.doc

IntroductiontoPCBLayout,SolderingandConstruction.doc

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IntroductiontoPCBLayout,SolderingandConstruction.ProtelALTIUMIntroductionPt2TheaimofthisexerciseistofamiliariseyourselfwithsomeofthebasicaspectsoftheProtelsoftwarepackage.Todothiswewilltaketheschematicfromthepreviousexercise,transferittoaPCBdesign.Wewillthenplaceandroutetheboardandproducefabricationfiles.BackgroundAsProtelmakesiteasiertodesignPCB’sitalsomakesiteasiertodesignbadPCB’s.WhenlayingoutaPCBitisimportantthatthecorrectfootprintsareusedintermsofelectricalconnectionsandinphysicaldimensions.Ifyouuseafootprintwithholesthataretoosmallthenyoucomponentwillnotfit,ifyouusepadsthataremuchtoobigthenthecomponentswillbehardtosolder.Withsurfacemountcomponentsitisimportantthatyoucheckthepadsizesarecorrectandallowplentyofroomforyoutosolderthecomponentbyhand(it’snogoodhavingatinysurfacemountPCBifyoucantgetyoursolderingirontotheactualcomponents).Ifyouareworkingathighfrequenciesyoumayhavetotakeintoconsiderationtheparasitic/straycapacitancesandinductancesformedbythePCBtracks.AlthoughProtelhascapabilitiestoAuto-placeandAuto-routeaboarditisreallynotadvisedyouusethesefacilitieswithoutplentyofpreplanning.ForthemostpartyouwillalwaysknowyourcircuitbetterthanProteldoes.Unlessyouhaveaverycomplicatedandunusuallylargecircuit,itwillbemuchfasterforyoutoplaceandroutetheboardbyhand.Thenormalprocedureforplacingandroutingtheboardisto:Checkfootprintslookcorrect.Placethecomponentsinamannersimilartotheschematiclayoutifpossible.CheckforanyobviousomissionstotheratsnestUntangletheRatsnestasmuchaspossibleRoutethelongestnetsfirst.Replacecomponentsasnecessary.Returntostep3ifneeded.ReCheckfootprints.Checkalldesignconstraints.Producefabricationfiles.Youwillgenerallyneedtomakeacoupleofattemptsbeforeyougetaboardthatyouarehappywith.Don’tworrythisisnormal.Inormallyreviseaboard3or4timesbeforesendingitoff.FigureSEQFigure\*ARABIC1PCBexampleshowingtheRatsNestTheratsnestisthecollectionoflinesbetweenthecomponentsshowingyoutheelectricalconnectionsasdefinedbytheschematic.Theratsnestlin