SMT缺陷及防范措施

2020/3/271SMTdefectsandcountermeasureSMT缺陷及防范措施2020/3/272IdentifySMTdefectsIdentifytheSMTdefectsaccordingtoIPC-A-610(Rev:D)根据IPC-A-610(Rev:D)确定缺陷．Thisstandardisacollectionofvisualqualityacceptabilityrequirementsforelectronicassemblies.IPC-A-610是关于电子组装外观质量验收条件要求的文件．2020/3/273ComponentPlacement15%ReflowsolderandCleaning15.2%SolderPasteScreening63.8%IncomingComponent5.7%Majorcontributortodefects缺陷的主要分布Source:MPM’sAuser’sguidetomorePreciseSMTprinting2020/3/274Knowthecommondefect了解常见缺陷类型Analysizethepossiblecause分析可能的原因Countermeasureforthedefects基于以上原因采取的对策LearningObjectives学习目的2020/3/275•Chipcomponentsstandingonaterminalend(tombstoning).片式元件末端翘起（墓碑）Tombstoning/立碑2020/3/276Countermeasure/对策Mechanism:Surfacetensionincomponentterminalisuneveninreflow.原理:在回流过程中零件两末端的表面张力不均衡.1.Componentterminalheatdistributedunevenly零件两末端受热分布不均衡.Insufficientsoaktime:Reflowprofileoptimization.保温区时间太短:优化回流曲线参数.2.PCBPaddesignissue(thepadsdistanceistoobig):improvePCBpaddesign.PCB焊盘设计问题(焊盘间距太大):改善PCB焊盘设计.Tombstoning/立碑2020/3/277Countermeasure/对策3.Componentterminaloxidizationorcontamination:SolderabilitytestifnecessaryandRTVthedefectmaterial.元件末端氧化或者受污染:根据情况做可焊性实验并且退还缺陷物料.4.Printingmisalignment:adjustprintingmachineparameters.丝印偏位:校正丝印机的参数.5.Placementmisalignment:OptimizetheP&Pmachineparameters.贴片偏位:优化贴片机的参数.6.Stencilaperturedesignissue:studyandimprovetheaperturedesign.钢网开孔的设计问题:研究并且改善开孔设计.Tombstoning/立碑2020/3/278•Asolderconnectionacrossconductorsthatwasjoined.焊锡在导体间非正常连接.•Solderhasbridgedtoadjacentnon-commonconductororcomponent.焊锡桥连到相邻的非导体或元件.Solderbridge/桥联2020/3/279Countermeasure/对策1.Screenprintingissue/丝印问题:a)PasteheightoutofUCL:Adjusttheprintertocontrolthepasteheight.锡膏高度超出控制上线:校正丝印机,控制锡膏高度.b)Pasteprintingmisalignmentorbridging:Finetuneprintingmachine./锡膏印刷偏位或者桥联:优化丝印机.c)Icicleprinting:Finetuneprintingmachineorchangetolowerviscositypaste.丝印拉尖:优化丝印机或者使用低粘性的锡膏.d)Solderpastecollapse:changetohigherviscositypaste./锡膏塌陷:使用高粘性的锡膏.e)Nonstandardstencilapertureopening:Studyandimprovetheaperture./不标准的钢网开孔:研究并改善开孔.Solderbridge/桥联Icicleprinting丝印拉尖Pastecollapse锡膏塌陷Bridging桥联Misalignment印刷偏位2020/3/2710Countermeasure/对策2.Pick&Placement/贴片a)Componentplacingmisalignment:FinetunetheP&Pmachine.元件贴片偏位:优化贴片机的参数.b)Highpressureforplacement:reducepressuretopropervalue.贴片压力过大:减少压力到适当的参数.3.Wavesoldering/波峰焊a)Lowconveyorramp:Raisetheconveyorrampperactualstatus.传送带角度过小:根据实际情况加大传送带角度b)Lessfluxonboard:Increasethefluxsprayvolumeonboardbeforegoingthroughwavesoldering.板上的助焊剂较少:波峰焊接之前加大助焊剂的喷射量Solderbridge/桥联2020/3/2711Componentdamaged(Nicks,cracks,orstressfractures)/元件损坏Nicks,cracks,orstressfractures.缺口，裂纹，压痕2020/3/2712Countermeasure/对策1.Rawmaterialdamaged:purgethebatchmaterial./来料损坏:清除这批来料.2.DamagedduringSMTprocess(Fixtureormachinetouchit):Investigateandtakecorrectiveactionsfornonstandardoperation.在SMT流程中损坏(夹具和设备接触):调查分析并且对不规范的操作作出矫正行动.3.Fastcoolingrateonreflowprocess:Controlthecoolingratetobelow4degreepersecond.在回流过程中冷却速率过快:控制冷却速度使斜率保持在每秒4度以下.Typicalreflowprofile/回流曲线典例:PreheatstageSoakstageReflowstagePeaktemp.Cooldown4oC/sComponentdamaged(Nicks,cracks,orstressfractures)/元件损坏2020/3/2713Misalignment偏位2020/3/2714Countermeasure/对策1.P&Pmachinefunctionunstable:FinetunetheP&Pmachine.贴片机性能不稳定:优化贴片机性能参数.a)FinetuneX,Ydata/调整X,Y坐标b)Optimizepickandplacementparameters./校正吸料和贴片的参数.2.Componentterminationoxidization:Solderabilitytestifnecessary.Purgethefailedmaterial/元件末端氧化:可焊性实验,清除不合格的来料.3.Operatortouchthecomponentpriortoreflow:Standardizetheoperatorhandling(documentcontrol)/在回流炉前目检操作员碰到贴片元件:标准化操作员操作(文件控制)4.Airflowrateinthereflowovenissohighthatthecomponentsaremoved.回流炉内空气流量太高以致吹偏了元件.Misalignment偏位2020/3/2715Componentleadlifted元件引脚翘高Oneleadorseriesofleadsoncomponentisoutofalign-mentandfailstomakecontactwiththeland.元件一个或多个引脚变形不能与焊盘正常接触．2020/3/2716Componentleadlifted元件引脚翘高Countermeasure/对策1.Componentleadbentbeforeplacement:Sortthedefectivepartandreturnittovendor.贴片前元件引脚变形:挑选出缺陷元件,退回供应商．2.Manualplacementtheloosepart:Inspectthepartbeforepassittoreflow.手放散料:回流前目检．2020/3/2717Solderball锡珠Solderballsarespheresofsolderthatremainafterthesolderingprocess.Solderballsviolateminimumelectricalclearance.焊锡球是焊接后形成的呈球状焊锡.Solderfinesaretypicallysmallballsoftheoriginalsolderpastemetalscreensizethathavesplatteredaroundtheconnectionduringthereflowprocess.焊锡残渣是在回流中形成的小的球状或不规则状焊锡球.2020/3/2718Solderball锡珠Countermeasure/对策1.StencilAperturedonotfocustopad:improvestencilapertureopening.钢网开孔没有对准焊盘中心:改善钢网开孔.2.Printingmisalignment:Finetuneprintmachine.丝印偏位:调整丝印机状态.3.Excesspaste:Cpkcontrol.多锡:Cpk控制.4.DampPCB:BakethePCBbeforeloadingittoSMT.PCB焊盘受潮:SMT组装流程之前烘烤PCB.6.Stencilpolluted:cleanthestencil.钢网脏污:清洗钢网.7.Profilerampupistoofast:Optimizereflowprofile.回流曲线升温速度过快:优化回流曲线.8.Pasteoxidized:exchangewithfreshsolderpaste.锡膏氧化:更换新锡膏.9.Chipwaveorsolderwaveheightistoohighcausedexcesssoldertotopside:adjustthewavesolderingheighttoproperlevel(wavesolder).波峰高度设置的太高致使多余的焊锡到顶面:校正波峰焊设置到适当的高度(波峰焊接).2020/3/2719Non-Wetting,Dewetting/虚焊，半润湿•Solderhasnotwettedtothelandorterminationwheresolderisrequired.虚焊:需要焊接的引脚焊盘不润