BTU-回流焊冷却斜率控制

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1、ControllingReflowOvenCoolingRatesNepconShanghaiApril25,2007RobDiMatteoProductManagerBTUInternationalCoolingControlWhyit’simportant?•Integralpartofthereflowprocess•Solderjointisnotformeduntilsolderiscooledbelowliquidustemperature•Longtermreliabilityinfluencedbycoolingrate•Producthandling–exittemperat

2、uresLeadFreeSoldersIt’sallaboutcontrol:TemperatureuniformityProcessrepeatabilityHeatingandcoolingratesAtmospherecontrolMaterialconsistencyReflowProfileCoolingStagesPeaktoliquidusLiquidustoexitExittoambientCoolingoccursfromPeakTemperaturedowntoambient!HeatingtheProductAllaboutBTU’sMovingthermalHeater

3、senergyfromtheheatertotheproductProductBeltCoolingtheProductAllaboutBTU’sRemovingthermalenergyfromtheproduct.ProductBeltCoolingRates•TypicalSMTCoolingRate–2-4°C/second•SlowCooling–0.5–1.9°C/second•FastCooling–4–6°C/secondTypicalCoolingProfilePeaktoLiquidus-2.0°C/second300250LiquidustocoolerexitC200-

4、2°C/secondSEER150GE100DExittemperature50-90°C0012345678MINUTESSlowCoolingProfilePeaktoLiquidus-0.5°C/second300250Liquidustoexit200-0.8°C/secondCSE150ERG100EDExittemperature50-150°C0012345678MINUTESFastCoolingProfileUltraFastCooling-5.0°C/second300250CoolingsectionCS200-2°C/secondEER150GED100Exittemp

5、erature50-80°C0012345678MINUTESCoolingRates•SlowCooling•FastCooling–Increasedformationof–Decreasesformationofintermetallicsintermetallics–Longertimeabove–Smallergrainsizeofliquidusthesolder–Reducedmaterial–Shortertimeabovestressliquidus–Higherexit–Materialstresses–temperaturesexpansioncoefficients–L

6、owerexittemperaturesOvenCoolingSystemsExternalCoolingZonesInternalCoolingZones•Directaircooling•WatercoolingviafanAdvantagesAdvantages•Simpledesign•Minimaltransitionareabetween•Lowercostpeakandcooling•Lessmaintenance•Helpswithnitrogencontainment•IncreasedheatremovalDisadvantages•Increasedadjustabili

7、ty–waterflowandtemperature•Heatexhaustedtoroom•DependantuponambienttemperatureDisadvantages•Limitedadjustability•Requireswatersource•Increasedmaintenance•Heatoftenmigratesoriscarriedintocoolerbyproduc