Thermal Design Consideration for Surface Mount Layouts

《Thermal Design Consideration for Surface Mount Layouts 》由会员上传分享，免费在线阅读，更多相关内容在学术论文-天天文库。

1、ThermalConsiderationsforSurfaceMountLayoutsCharlesMauney,TexasInstrumentsABSTRACTThefocusofthispaperistopresentthetechniquesthatareeffectiveinremovingtheheatfromthesurfacemountedpowerICsandtransferringittothecoolersurroundings.Inthepastthethermaldesignwasassi

2、mpleasaddingthethetavalues(°C/W)ofthepowercomponent,thepadandtheheatsinktogetherandmultiplyingbythepowerdissipatedinthatcomponenttoarriveatthetemperaturerisebetweentheambientandthejunctionoftheIC.Today,withsurfacemounttechnologyandICswithpowerpadsthePrintedCi

3、rcuitBoard(PCB)hasbecomeanintegralpartforremovingtheheat.EveryPCBisdifferentandthetaskofmathematicallyderivingatemperatureprofileforthePCBandeachpowercomponentisbeyondthescopeofthispaper.HoweverthebasicconceptsofwhatmakesagoodthermallyconductivePCB,somefirsto

4、rdermodelingexamplesandevaluationsofanexistingEVMwillhelpthedesignerunderstandthetechniquesinproducingagoodthermallyconductivePCB.Therearethreebasicmethodstomoveheatawayfromthesource,conduction,convectionandradiationheattransfer.Conductionismovingtheheatthrou

5、ghamaterial(PCB)typicallyfromcoppertoFR4tocopperandsoon.Convectionisforremovingtheheatoffthesurfacematerialtotheair.Radiationisformovingtheheatfromonesurfacematerialtoanotherthroughair.TABLE1THERMALCONDUCTIVITYFACTORSI.HEATTRANSFERBYCONDUCTIONMaterialsK(W/m°K

6、)K(W/in°C)ConductionisimportantbecauseitistheCopper3559surfaceareathateventuallydissipatestheheatAluminum1754.44andonlythroughconductiondoestheheatFR40.250.0064spreadouttotherequiredsurfacearea.TheSolder63/67391trendistomigratetowardsmallerpackagesAir0.02750.

7、0007believingthatthedesignareacanbereduced.Therealityisthatasmallerfootprint,withtheAtfirstglanceattheunits,itappearsthatsamepowerdissipation,requiresabetterPCBonewouldmultiplytheThermalConductivityconductiondesignandasimilaramountofFactorbythethermalpathleng

8、thtogetW/°Csurfacearea,foragiventemperaturerise.(1/θ),butthisisnotcorrectsincethiswouldHeatconductionisbetterthroughsomeindicatethelongerthethermalpaththelargermaterials(Copper)thanothers