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QFN/SON PCB Attachment - TI.com

ApplicationReportSLUA271A June2002 RevisedSeptember2007 QFN/SONPCBA ttachmentSteveKummerl,BernhardLange, (QFNs)andsmall-outlinenoleads(SONs)arele adlesspackageswithelectricalconnectionsm adevialandsonthebottomsideofthecomponent tothesurfaceoftheconnectingsubstrate(PCB ,ceramic).Thisapplicationreportpresentsu serswithintroductoryinformationaboutatta chingQFN/SONdevicestoprintedcircuitboard s(PCBs). (PCB) (HotGasConvectionandManual).. (MSL)..43 June2002 RevisedSeptember2007 June2002 STRUCTURE AND STITCH BONDST exasInstrumentsQuadFlatpackNoLeadsandSma ll-OutlineNoLeadsQuadflatnoleads(QFNs)an dsmall-outlinenoleads(SONs) ,numberofterminations, [printedcircuitboards(PCB),ceramic].Thes tandardQFN/SONpackagehasanexposedpadthat enhancesthethermalandelectricalcharacter istics, : June2002 RevisedSeptember2007 Box/Reel LabelsEE44 CustomerAssembly Site & Assembly Date Code (YYWW)JEDEC Pb-Free Logo & Finish CodeOrdered PNHigh-Temp& Low-TempMSL ,flat,plated, (morethan50percent) (fiducials) ,PCBthickness,andpeakreflowtemperatureac cordingtothemoisturesensitivitylevel(MSL )ofcomponents,componentdensity, ( ).

www.ti.com 3 Printed Circuit Board (PCB) Design Guidelines 3.1 Land Pad Styles 3.2 Land Pad Design S 6 5 9 DETAIL B D L (NE-1)x e DETAIL 1 6 5 3 Terminal Tip

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Transcription of QFN/SON PCB Attachment - TI.com

1 ApplicationReportSLUA271A June2002 RevisedSeptember2007 QFN/SONPCBA ttachmentSteveKummerl,BernhardLange, (QFNs)andsmall-outlinenoleads(SONs)arele adlesspackageswithelectricalconnectionsm adevialandsonthebottomsideofthecomponent tothesurfaceoftheconnectingsubstrate(PCB ,ceramic).Thisapplicationreportpresentsu serswithintroductoryinformationaboutatta chingQFN/SONdevicestoprintedcircuitboard s(PCBs). (PCB) (HotGasConvectionandManual).. (MSL)..43 June2002 RevisedSeptember2007 June2002 STRUCTURE AND STITCH BONDST exasInstrumentsQuadFlatpackNoLeadsandSma ll-OutlineNoLeadsQuadflatnoleads(QFNs)an dsmall-outlinenoleads(SONs) ,numberofterminations, [printedcircuitboards(PCB),ceramic].Thes tandardQFN/SONpackagehasanexposedpadthat enhancesthethermalandelectricalcharacter istics, : June2002 RevisedSeptember2007 Box/Reel LabelsEE44 CustomerAssembly Site & Assembly Date Code (YYWW)JEDEC Pb-Free Logo & Finish CodeOrdered PNHigh-Temp& Low-TempMSL ,flat,plated, (morethan50percent) (fiducials) ,PCBthickness,andpeakreflowtemperatureac cordingtothemoisturesensitivitylevel(MSL )ofcomponents,componentdensity, ( ).

2 (seeFigure13). (MSL)QFN/SONPCBA ttachment4 SLUA271A June2002 (PCB) BDL(NE-1)x eDETAIL 1653 TerminalTipTerminalTipEVEN TERMINAL SIDEODD TERMINAL SIDELee/2eDATUM A OR B(ND-1)x eN N-1E2E2/2D2/2D2 EXPOSED PADINDEX AREA(D/2 xE/2)-A--8-DD/24000 G 2xqqq C 2xE/2 EPrintedCircuitBoard(PCB) , thecopperdefinedornon-soldermaskdefineds tyle(NSMD)andthesoldermaskdefinedstyle(S MD).Theindustryhasdebatedthemeritsofboth stylesoflandpadsandalthoughTIrecommendst hecopperdefinedstylelandpad(NSMD), , ,bydefinition,alsoprovidesalargercopperp adareaandallowsthesoldertoanchortotheedg esofthecopperpads, , ,theside-viewdimensions(D,S,D2andL) June2002 RevisedSeptember2007 (PCB) (1) (1) (1)ThedimensionsZmaxandGminaretheoutside andinsidepadterminaldimensions, , ,1mmlongerthanthepackagelandlength(alsok nownasthetoelength)andbeextended0,05mmto wardsthecenterlineofthepackage(alsoknown astheheel).

3 TIusesatypicalvalueof0, ,05mm(0,025mmperside)widerthanthetermina lwidthonthepackage(seeFigure5).However,t oavoidsolderbridgingforcomponentshavingl eadpitchesof0,5mm,thepadwidthshouldbered ucedto0, ,28mmwidthwasbasedona0,5mmpitchcomponent havingamaxterminalwidthof0, 'tachieveasoldermaskwebbetween0,28mmwide pads,thewidthshouldbereducedtoaccommodat etheboardsupplier' , , June2002 mmMin mmPer Side for Lead PitchesGreater than 0,.65 (PCB) , , JA,isbasedonafour-layerPCBincorporatingv iasthatactasthethermalpathtothelayers, (CPL) , , ,however, ,itisrecommendedthatthethermalviasbeplac edonapitchofapproximately1, ,0,3mmdiameterdrillholesarerecommendedas astartingpoint, , , , , (OSP), , ,whichactivatesthemajorityofthefluxprior tothemeltingtemperatureofthealloy, June2002 RevisedSeptember2007 No TentingOSP Cross HatchSolder Mask PatternENIG w/Solder Mask Plugw/o plating over viaHASL No TentingENIG w/o vias OSP = Organic Solder (PCB) ,anon-soldermaskdefinedpad(NSMD)isrecomm endedoversoldermaskdefined(SMD) , ,buttypicallytheNSMD openingsare0,1mmto0, ,5mm,itisrecommendedtodesignthesoldermas karoundallpadsoneachsidewithaclearanceof 0,05mmorsmaller, ,itisnecessarytoroundtheinnercorneroneac hrow(seeFigure7).

4 Thisensuressufficientsoldermaskinthecorn erofthePCBfootprintdesignandalsoprevents themetalfeaturefromencroachingbeyondanai rgapof0, ,ithasbeenobservedthatsomeQFNconfigurati onsutilizeanexposedmetalpin1featurebenea ththecomponent, ,TIrecommendsmaintainingaroutingandviake ep-outareabypin1onallQFNdesignstoguardag ainstthisriskandoffermoreflexibilitywhen selectingdifferentsuppliers(seeFigure7). June2002 Excessive BendingAvoid Excessive BendingPrintedCircuitBoard(PCB) ,unevensolderpastethickness, (OSP)coating,electrolessnickel/immersion gold, "dryfilmprocess." : Shelflife Permanentcoverageofcopperviasandotherfea turesnotexposedtoasolderprocess,and ContaminationresistanceEvenwiththesediff erences, , , (seeFigure8). June2002 RevisedSeptember2007 Apertures Should be Tapered toStencilPCBCSide ,no-cleansolder(SN63/Pb37orSACalloy)past eiscommonlyusedinmountingQFN/SON,however , , , srecommendedtemperatureprofilebeusedtoop timizefluxactivitywithintheMSL(moistures ensitivitylevel) , ,aswellasthestencilopeninggeometry, , ,whichhelpstoensureuniformreleaseoftheso lderpasteandreducesmearing(seeFigure9).

5 Thesolder-jointthicknessofQFN/SONleadfin gersistypicallybetween0,050mmto0,075mm, ,100mmto0,150mm( )range,withatypical0,125mmstencildesignf or0, , (suchasstainlesssteel). ,astencilthicknessof0,125mm( ) June2002 Foil ThicknessWidth of Aperture OpeningAspect Ratio =2 x (L + W) x TW x L=Area of Aperture WallsArea of Aperture OpeningArea Ratio = , ,1:1(Note:1:1isrecommendedonperipherylea dfingersandnotthecenterthermalpad ).Forfine-pitchQFN/SONcomponentsof0,5mma ndbelowitmaybenecessarytoreducethestenci lapertureby20%topreventshortingbeneathth eQFN, , ,4mmpitchcomponents,apadwidthof0,2mmisre commendedtoaidsolder-pasteprintingandtoa chieveagapof0, ,ona0,5mmpitchdevicewith0,85mmx0,28mmwid epads,astencilapertureof0,23mmx0,8mmandt hicknessof0,125mmshouldbeusedtoachievead equateprintvolumeandarearatiorequirement sasoutlinedinIPC-7525(seeFigure10).Incas eswheretheboardlandpatternmustbeminimize d, , (seeFigure10) (seeIPC-7525).

6 Thehigherthearearatio,thebetterthesolder pastewillrelease, ,thehigherthearearatiowillbe,ultimatelyr esultinginarobustsolder-pasterelease.(Re fIPC-7525) , ,thesolder-pastecoverageisapproximately5 0%to70%ofthepadarea(seeFigure11).Designi nganaperturethatprintssolder1:1withtheex posedpadresultsinexcessivemetalvolumetha twill float thepart, ,theamountofvoidingpostreflowinthetherma lpadsolderjointshouldnotexceed50%inhighp owerapplications(tobeverifiedusinganx-ra y).BasedonaJEDECHighKboardstackup,25%has beendeterminedtobeapointofdiminishingthe rmalperformancereturns,butTIprefersalimi tof50%tobeset(referenceJESD51-7).SLUA271 A June2002 RevisedSeptember2007 June2002 (theta) (lessthan50percentoffthepadcenter)automa ticallyselfalignduringreflow(seeFigure12 ).Grosslymisalignedpackages(greaterthan5 0percentoffpadcenter)mustberemovedpriort oreflow,astheymaydevelopelectricalshorts resultingfromsolderbridges, : Packagesilhouette,alsocalled backlighting.

7 Thevisionsystemlocatesthepackageoutline. Lead-framerecognition,alsocalled frontlighting. , , , ,iftherearemultiplepackagesontheboard, ,locationofthedeviceontheboard, , (seeFigure13) , , (assumingtheuseofadouble-sidedPCB) June2002 RevisedSeptember2007 ReflowDuring ReflowAfter Reflow183165 Time135 Temperature ( C)Min. 60 120 235 C, Min. 195 C Min. 30 90 60 120 260 C, Min. 230 C Min 30 90 ( C)Pb-Free Temperature Profile ExampleSnPb Temperature Profile ,no-cleansolderpasteisused, (CFC), , scontrol, , , ,x-rayinspectionisusedtoestablish14 QFN/SONPCBA ttachmentSLUA271A June2002 ,shorts,opens, (AOI). , , , ,suchasfluxactivity,soldervolumes, scontrol, , ,thesolderjointunderneathisnotaffected(s eeFigure14). June2002 RevisedSeptember2007 (HotGasConvectionandManual) (HotGasConvectionandManual) ,suchascomponentremoval,siteredress,sold erpaste/fluxapplication,alignment,compon entplacement, ,suchascharacterizingandstoringindividua lcomponentreflowprofiles, , , , , , , , , C,nozzlewarmingup20%airflow,125 20%airflow,225 C, 20%airflow,335 C, 25%airflow,370 C, ,lowervacuumnozzle, 40%airflow,25 C, , June2002 (HotGasConvectionandManual)OncetheQFN/SO Nhasbeenremoved, , , ,oneofthesetwomethodscanbemoreadvantageo us, , ,thesolderpasteisshownappliedtothepartus ingafixturecourtesyofPhotoStencil.

8 ,theinsertiontooleliminatesmanualhandlin gofthecomponent, , , (Figure16) , June2002 RevisedSeptember2007 Air-Vac Rework Nozzlefor QFN Package sizes between mm to mm NMX188 DVG- .188 Exhaust Opening-- VTMX020-35 Vacuum TipA larger nozzle will be requiredfor larger package to recommended nozzle sizesby package dimensionUsed for QFN Package sizesbetween mm to mmHot Gas Convection NozzleReworkGuidelines(HotGasConvectiona ndManual) June2002 (HotGasConvectionandManual) , C,nozzlewarmingup20%airflow,125 20%airflow,225 C, 20%airflow,335 C, 25%airflow,370 C, 40%airflow,25 C,50sIfmanualtouchupisrequired,itishighl yrecommendedtobakeouttheboardandreplacem entcomponentspriortorework, (seeFigure17) ,thesolderingirontipsizeandpotentialfort emperatureovershootcanbereduced, , , (seeFigure18).Ifmanualsolderingisused, June2002 RevisedSeptember2007 (HotGasConvectionandManual) June2002 RevisedSeptember2007 SubmitDocumentationFeedbackIMPORTANTNOTI CET exasInstrumentsIncorporatedanditssubsidi aries(TI)reservetherighttomakecorrection s,modifications,enhancements,improvement s, , , ,eitherexpressorimplied,isgrantedunderan yTIpatentright,copyright,maskworkright,o rotherTIintellectualpropertyrightrelatin gtoanycombination,machine, , ,conditions,limitations, (suchaslifesupport)whereafailureoftheTIp roductwouldreasonablybeexpectedtocausese verepersonalinjuryordeath, ,andacknowledgeandagreethattheyaresolely responsibleforalllegal,regulatoryandsafe ty-relatedrequirementsconcerningtheirpro ductsandanyuseofTIproductsinsuchsafety-c riticalapplications, , "enhancedplastic.

9 " 'srisk, ,iftheyuseanynon-designatedproductsinaut omotiveapplications, :TexasInstruments,PostOfficeBox655303,Da llas,Texas75265 Copyright 2007,TexasInstrumentsIncorporat


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