How To Design Thermal Reliefs | Tempo Automation

A thermally relieved pad is an SMT pad with the copper around it removed (“relieved”) except for 2–4 traces. Adding thermal relief to pads that will have ... HowtoDesignThermalReliefswithMinimalManufacturingIssues WRITTENBY: TempoAutomation RelatedResource: TheEngineer'sGuidetoPCBAManufacturingComplexity DownloadNow Electroniccomponentsbecomesmallerandsmallereveryyear;themarket,inturn,demandselectronicswithever-shrinkingformfactors.PCBswithdimensionsunderanincharecommonplace,andtheirsurfacesaregrowingmoretightlypackedwithplacements.Somedesigners,intheinterestofsqueezingslightlymorespaceoutofasmallarea,areleavingoutthermalreliefs — butthiscanbeabiggermistakethanitseems. AthermallyrelievedpadisanSMTpadwiththecopperarounditremoved(“relieved”)exceptfor2–4traces.Addingthermalrelieftopadsthatwillhavecomponentssolderedtothemiscrucialindirectingandcontrollingtheflowofheatthroughyourboardduringreflow.Padswithpoorthermalreliefmaynotheatevenlyinthereflowovenandcausetombstoning,no-connects,orpoorsolderjoints,whichrequiremanualrework.Reworkisthenimpededbyalackofthermalreliefaswell.Addingthermalrelieftoyourdesigncanreducequalityproblemsaswellasthetimeneededtorepairthem. Theuseofthermalreliefforthesepadswillmakereworkeasierandquickerbyeliminatingthehigherconductivityandtimeittakestoheatupallormostofacopperpour,aswithasoldermaskdefinedpad.Asinglepadwiththermalreliefwillreachthecorrecttemperaturemuchmorequickly.Iftherearecomponentpadsnexttoeachotherthatsharethesamecopperpour,itcanbeverytime-consumingtoheatupapad,evenforexperiencedtechnicians.Insomecasesreworkmaynotbepossibleduetotheamountofheatandtimeittakestobringapaduptotemperaturewithoutthermalrelief — componentsand/ortheboard’ssurfacecaneasilysufferdamagefromtheextendeduseofasolderingiron.Thermalreliefforpadsiseasytoimplement,andstronglyrecommendedforanyelectricalcomponentthatdoesn’trequireahighvoltagecurrent.Withhighercopperweights,thermalreliefmaysavehoursofreworktimeandalsohelpeasetheinitialsolderingprocess. Formulaefordesigningthermalreliefs ThisisthesuggestedformulafordesigningthermalreliefsthatweuseatTempoAutomation,whichfollowsIPC-2222standards. Thermalconnectingtracewidth: X=OveralllengthoftheXorY-axisofanSMTPad(Imperial/metric). Y=Quantityofthermalconnectingtraces. T=60%ofthepadsize. Z=Tracewidth(T/Y) (X*0.60)/Y=Z Example: Wehavea .040”x .040”SMTpad,sowewilltakethelengthofeithertheX-orY-axisandplugitinto‘X’.(Forthisexample,wetaketheX-axislength.)Weneed4thermalconnectingtraces,so‘Y’willbe4. (.040* .60)/4=Z .024/4=Z .006”=Z Thermalreliefsize: X=OveralllengthoftheX-orY-axisofanSMTPad(imperial/metric). TR=Distancefromthermalreliefpadtocopperpour(thismustnotexceedtheminimumof .005”) X* .25=TR Example: Wehavea .040”x .040”SMTpad,sowewilltakethelengthofeithertheX-orY-axisandplugitinto‘X’.(Forthisexample,wetaketheX-axislength.) .040* .25=TR .010”=TR TheEngineer'sGuidetoPCBAManufacturingComplexity DownloadNow   ReadMore BlogPCBManufacturing PCBLayoutGuidelinesforPowerSupplyApplications BlogIndustrial BuildingCustomElectronicsforIndustrialAutomationandRobotics BlogPCBManufacturing BestPCBDielectricMaterialsforHighSpeedApplications AerospaceAerospace BestTypesofPressureSensorsUsedforAerospaceApplications BlogPCBManufacturing DesigningPressureTolerantElectronicsforHarshConditions AerospaceAerospace AdheringtoSpace-GradeRadiationProductDesignStandardsforElectronics BlogPCBManufacturing TheNextGenerationofElectricPowerGridDesigns ThelatestPCBnewsdeliveredtoyourinbox. PCBAServices TurnkeyAssembly RapidPrototyping On-DemandManufacturing SupplyChainSolutions Capabilities OurCapabilities Certifications TheDigitalThread Industries Automotive Aviation&Defense ConsumerElectronics DesignFirms Energy IndustrialTechnology MedicalDevice Semiconductor Space Resources HowToOrder FrequentlyAskedQuestions VirtualFactoryTour CaseStudies WebinarsandDemos eBooksandWhitePapers Blog AboutUs InvestorRelations WhoWeAre Leadership Careers Newsroom Search SignIn