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1、補(bǔ)充說明:因隨著製程的發(fā)展本教材中部分參數(shù)可能和實(shí)際狀況有偏差,請參考材料的spec.ProfileCurveForSMTREFIOW形式(HEATER分佈)183oC170oCPreheatingSoakingPeakCoolingPreheating:Solventevaporation溶劑揮發(fā)Soaking:FluxreducesandMetaloxides助焊劑還原金屬氧化物Peak:Solderballsmelt,wettingandwickingbegin.&Soldermeltingcompletes,surfacetensiontakesover.錫球熔化,浸潤
2、開始,焊接進(jìn)行,表面張力起作用Cooling:Cooldownphase.快速冷卻階段140oCReflow的製程條件針對IntelRG82845BGAsoakzonetime:50~65sec;xxxxxx規(guī)範(fàn):PreheatingZone:*SolderPastes’Viscosity錫膏黏度:1.Solventevaporationcauseviscosityhigher.溶劑揮發(fā)使黏度變大2.Heatingsolventwillcauseviscositydown.加熱溶劑會使黏度降低HighheatingrateViscosityLowheatingrateTempe
3、rature預(yù)熱段各種錫膏在預(yù)熱段要求的升溫速律及進(jìn)入恆溫區(qū)的溫度並不盡相同，其主要取決於溶劑(Solvent)的揮發(fā)溫度以及松香(Rosin)的軟化點(diǎn)。因松香在進(jìn)入恆溫區(qū)的建議溫度時(shí)間時(shí)軟化，錫膏裡的溶劑尚是液態(tài)，此時(shí)錫膏為固液態(tài)，因此黏度最低，錫膏流動特性最佳，若預(yù)熱段升溫速率過高，錫膏黏度太低，流動特性太好，易造成Slump效應(yīng)，進(jìn)而產(chǎn)生短路及R/C旁擠出邊球，此時(shí)可適度將預(yù)熱段溫度降低，將有助於減少短路及SideBoll產(chǎn)生。*Fluxsoftnesspoint:Fluxsoftnesspointwilldecreasesolderpasteviscosity.助焊劑(
4、松香)軟化會降低錫膏黏性HighheatingrateLowheatingrateVerylowheatingrateViscosityTemperatureSoakingZone:1.Solventevaporatecompletely溶劑完全揮發(fā)2.Fluxactivationandoxidation助焊劑被激活並去氧化3.Soakingtimeandtemperature3.1ForN2oventheSoakingtimecanbelonger.3.2ForAiroventheSoakingtimeshouldshorterthanN2oven4.PCBboardbend
5、ingcontrolPCB板彎控制BeforeSoakingAfterSoakingPCBPCB恆溫區(qū)恆溫區(qū)其目的再於使PCB上所有的零件溫度達(dá)到均溫，簡少零件熱衝擊，恆溫區(qū)的長度則取決於PCB面積的大小。 此時(shí)錫膏內(nèi)劑不斷揮發(fā)，活性劑持續(xù)作用去氧化，松香軟化並披覆在銲點(diǎn)上，具有熱保護(hù)及熱傳媒的作用。恆溫區(qū)*PlasticBGAAfterSoakingPlasticBGAPCBbending由於PP的軟化溫度點(diǎn)為140℃,故如可考慮縮短Over140℃的時(shí)間來改善空焊,此為一嶄新觀念,其實(shí)這種方法在實(shí)踐中被証明是有效的.SoakingZone:*Homologousheatin
6、g(PCB,Componentsandsolderpaste)溫度達(dá)到一致(機(jī)板,零件,錫膏)*Solderpasteviscositycontrol錫膏黏性控制*Solderwettingandwickingbegin.錫膏浸潤開始*Surfacesolderballsmelting.表面焊料金屬熔融SoakingZonePlasticBGAsubstrate(Tg:1750C)PCBbending1232Lead>1Body>3PadNormalsolderingWickingBridgebywickingMoreheatfromthebottomLessheatfromt
7、hetop2Lead>1Body>3Pad3Pad>2Lead>1BodyParametersetting:Tombstoning:T1T3dT2Conditionwhichcausestombstoningshallbe:T1+T2>T3Inordertoovercometheproblem,themomentumrelationmustbecomeasbelow;T1+T2=T3T1+T2>T3T1T3dT2Partialmelting*PeaktemperatureandReflowt
