IntroductionToPCBLayout,SolderingandConstruction.PCBLayoutBASICSWhendesigningaPCBeachcomponentontheboardhasafootprint.Thisisthespaceandconnectionsofthedevicewhenplacedontheboard.Thefootprintcontainsinformationsuchasifthecomponentisthroughhole(e.g.standard1/4Wresistors,DILchips)orsurfacemount(e.g.805chipcapacitorsandresistors,SOICchips).Italsoshowshowmuchphysicalspacethecomponentmaytakeupontheboard.SomeexamplefootprintsareshowninFigure1below.FigureSEQFigure\*ARABIC1CommonPCBfootprintsshownona0.1"grid.Theareaofcopperwherethecircuitconnectstotheleadsofthecomponentisknownasapad.Forthrough-holecomponentsthepadusuallyconsistsofacircleofcopperwithaholedrilledthrough.Forsurfacemountcomponentsthepadisusuallyasmallrectangleofcopperwithoutahole.Althoughitmayseemobvious,itisworthnotingthataholebyit’sverynaturemustexistonboththetopandbottomlayersofaduallayerPCB.Surfacemountpadsonlyexistononelayersoit’spossibletorunaconnectionbeneathsurfacemountpadsonotherlayers,whichisoneoftheirmainadvantagesbesidesbeingmuchsmallerinsize.AnotherkindofpadisusedonPCB’sthatissimilartothatusedforthrough-holecomponentsbuthasaholediametermuchtoosmallforanycomponent.Thishole/padcombinationisusedtomoveasignalfromthetoplayertothebottomlayerandiscalledavia.TheconnectionsbetweenpadsandviasonaPCBarecalledtracks.TracksarethewiresofthePCBworldandshouldasageneralrulebekeptthicktokeepresistancelowandimprovephysicalstrength.TheprocessofplacingtracksbetweenthepadsofcomponentsinaPCBdesignisknownasrouting.Whenacomputerdoesthisautomaticallythisisknownasautorouting.Figure2belowshowssomeexamplesoftracks,padsandvias.NotethatthetextontheBottomlayer(showninblue)isreversed.ThisisdoneasPCB’saretraditionallydesignedfromthetoplayerlookingdownonthecomponentsasiftheboardwasmadeofglass.Whenmakingyourownboardsitisalwaysveryhelpfultoplacesometextonthelayerssothatyoucantellyouhavethenegativeroundthecorrectway.(APCBmadewithnegativereversedisworthlessin99.9%ofcases)FigureSEQFigure\*ARABIC2ExampleTracks(50mil),P