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1、IPC7351BGenericRequirementsfSurfaceMountDesignLPatternStardFINALDRAFTFINDUSTRYREVIEW–AUGUST20091SCOPEThisdocumentprovidesinfmationonlpatterngeometriesusedfthesurfaceattachmentofelectroniccomponents.Theintentoftheinfmatio
2、npresentedhereinistoprovidetheappropriatesizeshapetoleranceofsurfacemountlpatternstoinsuresufficientareaftheappropriatesolderfillettomeettherequirementsofIPCJSTD001alsotoallowfinspectiontestingrewkofthosesolderjoints.1.1
3、PurposeAlthoughinmanyinstancesthelpatterngeometriescanbedifferentbasedonthetypeofsolderingusedtoattachtheelectronicpartwhereverpossiblelpatternsaredefinedwithconsiderationtotheattachmentprocessbeingused.Designerscanuseth
4、einfmationcontainedhereintoestablishstardconfigurationsnotonlyfmanualdesignsbutalsofcomputeraideddesignsystems.Whetherpartsaremountedononebothsidesoftheprintedboardsubjectedtowavereflowothertypeofsolderingthelpatternpart
5、dimensionsshouldbeoptimizedtoinsurepropersolderjointinspectioncriteria.Lpatternsaredimensionallydefinedareapartoftheprintedboardcircuitrygeometryastheyaresubjecttotheproducibilitylevelstolerancesassociatedwithplatingetch
6、ingassemblyotherconditions.Theproducibilityaspectsalsopertaintotheuseofsoldermasktheregistrationrequiredbetweenthesoldermasktheconductpatterns.Note1:Thedimensionsusedfcomponentdeionshavebeenextractedfromstardsdevelopedby
7、industrialstardsbodies.Designersshouldrefertothesestardsfadditionalspecificcomponentpackagedimensions.Note2:Facomprehensivedeionofthegivenprintedboardfachievingthebestpossiblesolderjointstothedevicesassembledthewholeseto
8、fdesignelementsincludesbesidethelpatterndefinition:?Soldermask?Solderpastestencil?Clearancebetweenadjacentcomponents?Clearancebetweenbottomofcomponentprintedboardsurfaceifrelevant?Keepoutareasifrelevant?Suitablerulesfadh
9、esiveapplicationsThewholeofdesignelementsiscommonlydefinedas‘‘mountingconditions.’’Thisstarddefineslpatternsincludesrecommendationsfclearancesbetweenadjacentcomponentsfotherdesignelements.Note3:Elementsofthemountingcondi
10、tionsparticularlythecourtyardgiveninthisstardarerelatedtothereflowsolderingprocess.Adjustmentsfwaveothersolderingprocessesifapplicablehavetobecarriedoutbytheuser.Thismayalsoberelevantwhensolderalloysotherthaneutectictinl
11、eadsoldersareused.Note4:Thisstardassumesthatthelpatternfollowstheprinciplethatevenunderwstcaseconditionstheoverlapofthecomponentterminationthecrespondingsolderinglwillbecomplete.Note5:Heatdissipationaspectshavenotbeentak
12、enintoaccountinthisstard.Greatermassmayrequireslowerprocessspeedtoallowheattransfer.Note6:Heaviercomponents(greaterweightperl)requirelargerlsthusaddingadditionallpatternsurfacewillincreasesurfaceareaofmoltensoldertoenhan
13、cecapabilitiesofextraweight.Insomecasesthelsshowninthestardmaynotbelargeenoughinthesecasesconsideringadditionalmeasuresmaybenecessary.1.2DocumentationHierarchyThisstardidentifiesthegenericphysicaldesignprinciplesinvolved
14、inthecreationoflpatternsfsurfacemountcomponentsissupplementedbyasharewareIPC7351LPatternCalculatthatprovidesthroughtheuseofagraphicaluserinterfacetheindividualcomponentdimensionscrespondinglpatternrecommendationsbasedupo
15、nfamiliesofcomponents.TheIPC7351LPatternCalculatisprovidedonCDROMaspartofthisstard.UpdatestolpatterndimensionsincludingpatternsfnewcomponentfamiliescanbefoundontheIPC1.Exactdetailsbasedonindustrycomponentspecificationsbo
16、ardmanufacturingcomponentplacementaccuracycapabilities.TheselpatternsarerestrictedtoaspecificcomponenthaveanidentifyingIPC7351lpatternname.2.Equationscanbeusedtoalterthegiveninfmationtoachieveamerobustsolderconnectionwhe
17、nusedinparticularsituationswheretheequipmentfplacementattachmentaremelessprecisethantheassumptionsmadewhendeterminingthelpatterndetails(see3.1.2).Threelpatterngeometryvariationsaresuppliedfeachofthedevicefamiliesmaximuml
18、protrusion(DensityLevelA)medianlprotrusion(DensityLevelB)minimumlprotrusion(DensityLevelC).BefeadaptingtheminimumlpatternvariationstheusershouldconsiderproductqualificationtestingbasedontheconditionsshowninTable324.Densi
19、tyLevelA:Maximum(Most)LProtrusion–Flowdensityproductapplicationsthe‘maximum’lpatternconditionhasbeendevelopedtoaccommodatewaveflowsolderofleadlesschipdevicesleadedgullwingdevices.Thegeometryfurnishedfthesedevicesaswellas
20、inward‘‘J’’fmedleadcontactdevicefamiliesmayprovideawiderprocesswindowfreflowsolderprocessesaswell.DensityLevelB:Median(Nominal)LProtrusion–Productswithamoderatelevelofcomponentdensitymayconsideradaptingthe‘median’lpatter
21、ngeometry.Themedianlpatternsfurnishedfalldevicefamilieswillprovidearobustsolderattachmentconditionfreflowsolderprocessesshouldprovideaconditionsuitablefwavereflowsolderingofleadlesschipleadedgullwingtypedevices.DensityLe
22、velC:Minimum(Least)LProtrusion–Highcomponentdensitytypicalofptablehheldproductapplicationsmayconsiderthe‘minimum’lpatterngeometryvariation.ionoftheminimumlpatterngeometrymaynotbesuitablefallproductusecategies.Theuseofcla
23、ssesofperfmance(123)iscombinedwiththatofcomponentdensitylevels(ABC)inexplainingtheconditionofanelectronicprintedboardassembly.AsanexamplecombiningthedeionasLevels1A3B2Cwouldindicatethedifferentcombinationsofperfmancecomp
24、onentdensitytoaidinunderstingtheenvironmentthemanufacturingrequirementsofaparticularprintedboardassembly.AlthoughallthreelpatterngeometryvariationsareconsideredcompliantfleadfreesolderingprocessestheDensityLevelCvariantw
25、illrequiremeprocessingcapabilitytoensureaproperwettingoftheleadfreealloy.Itisimptanttonotehoweverthattheprimaryissueofleadfreerelatestothesurfacefinishontheprintedboardthecomponenttermination.See3.2.3ffurtherinfmationonl
26、patterndesigninleadfreesolderingenvironments.Note:ItistheresponsibilityoftheusertoverifytheSMTlpatternsusedfachievinganundisturbedmountingprocessincludingtestinganensuredreliabilityftheproductstressconditionsinuse.Inaddi
27、tionthesizeshapeoftheproposedlpatternmayvaryaccdingtothesoldermaskaperturethesizeofthelpatternextension(dogbone)theviawithintheextensioniftheviaisinthelpatternitself.Alsotheusageofoblongroundedlpatternpadsisconsideredadv
28、antageousfleadfreesolderingprocessesincomparisonwithrectangularpadsastheoblongshapeprovidesfapullofthesolderonthepad.Anexceptiontothisruleiswhentheheelptionofthelpatternhastobetrimmedduetowhenthecomponentbodystoffislesst
29、hanthepastemaskstencilthicknesstheheelhastobetrimmeddueto“ThermalPad”interference.Inthesetwocasestherectangularpadshapeispreferredtocompensatefthereductionincopperareaofthelpatternpadlength.1.5TermsDefinitionsTermsdefini
30、tionsusedhereinareinaccdancewithIPCT50exceptasotherwisespecified.Note:Anydefinitiondenotedwithanasterisk()isareprintofthetermdefinedinIPCT50.AsAgreedUponBetweenUserSupplier(AABUS)Indicatesadditionalalternaterequirementst
31、obedecidedbetweentheuserthesupplierintheprocurementdocumentation.Examplesincludecontractualrequirementsmodificationstopurchasedocumentationinfmationonthedrawing.Agreementscanbeusedtodefinetestmethodsconditionsfrequencies
32、categiesacceptancecriteriawithinatestifnotalreadyestablished.Assembly–Anumberofpartssubassembliescombinationsthereofjoinedtogether.(Note:Thistermcanbeusedinconjunctionwithothertermslistedhereine.g.‘‘PrintedBoardAssembly.
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