外文翻译水平处理技术创新.docx

外文翻译水平处理技术创新.docx

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外文翻译水平处理技术创新

Aninnovationinhorizontalprocessing

PeterLymnandKenBishop

CEMCOFSLLtd,Waterlooville,UK

Abstract

Purpose–Thepurposeofthispaperistodetailaninnovativenewequipmentenhancementforuseinthehorizontalprocessingofprintedcircuitboards（PCBs）.

Design/methodology/approach–Thepaperdescribesanon-contactlaminarorstreamlineflowprocesschamber.Italsodescribesatransportandguidingmethodsuitableforboththickandthinmaterialsandexpandsonthemechanicsandfluiddynamicsthatfurtherreduceequipmentlengthandoperatingcost.

Findings–Thenewprocesschamberanditsrelatedenhancementsresultinafasterandmoreuniformchemicalreactionthanisobtainablewithconventionalfloodchambers.Thisenablestheequipmenttohavereducedlengthandtoofferreducedoperatingcosts.

Originality/value–Thepaperpresentsanewapproachtohorizontalprocessingthatcanofferreducedequipmentfootprintsandreductionsinoperatingcosts.

KeywordsProcessmanagement,Printedcircuits,Conveyors,Chemicaltechnologyprocess

Introduction

Printedcircuitboard（PCB）fabricatorshaveusedhorizontalrollerconveyerstotransportcoppercladlaminatethroughchemicalspraytreatmentchambersformanyyears.Thesesimpleconveyorisedsprayprocessorshaveevolvedovertimetoaccommodatemuchthinnermaterials,butthecomplicationofguidingandsupportingthemthroughsprayjetsgenerallymeanstwotypesofmachinearerequired;oneforthick,rigidmaterialandanotherlonger,morecomplexsystemforverythinorflexiblesubstrates.Morerecently,thistypeofequipmenthasbeenfurtheradaptedtoincorporateimmersionchambersforplatingandothersurfacetreatmentprocesseswheresprayjetsarenotsuitable.Theneedtocontainthestaticheadabovetherollertransportsystemandtherelativelylongcontacttimesrequiredforimmersionprocessesmakethesesystemsevenlongerandmorecomplex.Thispaperdescribesanon-contactlaminarorstreamlineflowprocesschamberthatresultsinafasterandmoreuniformchemicalreactionthanisobtainablewithconventionalfloodchambers.Italsodescribesatransportandguidingmethodsuitableforboththickandthinmaterialsandexpandsonthemechanicsandfluiddynamicsthatfurtherreduceequipmentlengthandoperatingcost.

Chemicalprocesschamber

Inconventionalimmersionchambers,fluidispumpedfromasumptoadammedrollerconveyorchamber.Thesolutionistypicallyre-circulatedatarateoffivetimesthechambervolumeperminutethroughmanifoldspositionedbetweenconveyorrollers.Transportationisachievedbyusingrollerwheelsto

avoidexcessivemaskingofthepanelbeingprocessed.Thiscombinationoffloodedjetandrollerwheeltransportresultsinchaoticturbulentzoneswithinarelativelystagnantbathandcanleadtovariablechemicalreactionacrossthepanel.The“FluidEngine”immersionchambers,bycontrast,providelaminarflowupto100×thechambervolumeperminuteorinexcessof11mperminute,resultinginfaster,moreuniformreactions.Theenginecomprisestwoplatesclosedateachsidetoformanarrowchamber.Fluidcontainmentrollers,mountedattheentryandexitofthechamber,pushandpullbothflexibleandrigidmaterialsthroughit.Fluidisinjectedatthecentreofeachplateproducingalaminarflowtowardstheentryandexitendsofthechamber（Figure1）.

Thislaminarflowresultsinsteadyboundarylayersaboveandbelowthematerialbeingprocessed,helpingtoguideitthroughtheprocesschamber.TheleadingandtrailingedgesoftheplatesareshapedtoproduceaCoandaeffect,divertingtheboundarylayerdiffusionpointawayfromthepanelentryandexitzones.Thismaintainsthestreamlineflowanddivertsfluidabovetheplates,preventingfloodingandmaterialdeflection.TheCoandaeffectwasdiscoveredbyHenri-MarieCoanda,aRomanianbornaeronauticalengineer,andisnamedafterhim.TheCoanda,orwallattachment,effectisthetendencyforamovingfluidtoattachitselftoasurfaceandflowalongit.Whenafluidmovesacrossasurface,africtionalforceoccursbetweenthefluidandthesurfaceandslowsitdown.Thisresistancetotheflowpullsthefluidtowardsthesurface,causingthefluidtosticktothesurface.Therefore,afluidflowingfromanozzlewillfollowanearbycurvedsurfaceifthecurvatureofthesurfaceisnottoosharp.

Figure1Diagrammaticviewofthefluidengineshowingthelaminar

flowandtheCoandaeffect

Dualfeedengine

Somechemicalprocessesassociatedwiththeprintedcircuitindustryrequireagas（normallyoxygenintheformofair）tobeintroducedatthepointofcontactofthechemicalwiththepanelbeingprocessed.Adualfluidversionofthe“StreamlineFluidEngine”thatsimultaneouslyfeedsgasandliquidtothedischargeslotsprovidesthisfacility,whilemaintainingthecharacteristicsassociatedwiththestandard“FluidEngine”.ThedesignofthisengineisshowninFigure2.

Thegasisfedunderpressuretotheoutergasplenum（showningreen）thatisseparatedfromtheliquidplenumbyapermeablemembrane.Thebaseplatehasaseriesofcloselyspacedholesthatnormallyconnectthebaseplatedirectlytotheliquidplenumacrossthewidth.Inthedualfeedheadtheliquidplenumhasaseriesoftubesthatconnectthegasplenumtothebaseplate.Thesetubesarepitchedsuchthattheylineupwitheveryotherholeinthebaseplateandsealtheholesfromtheliquidintheplenum.Therefore,gasandliquidaredeliveredsidebysideacrossthewidthofthepanelthroughalternateholes.Figure2showshowbothgasandchemicalreachtheoutputjets.Thelowerheadshowsthepaththatthegastakestoreachthejetsandtheupperheadshowshowthechemicaldoes.Gasisshownasgreenandchemicalasblue.

Figure2Dualfluidenginetointroduceagasintothechemicalstream

Fluidknife

Whereitisnecessarytoremovechemicalsfromthepanelbydilution,orwherehighfluidimpingementisrequiredtowetblindfeatures,ashorterversionofthefluidengine,knownasafluidknife,isused.Typically,thisfluidknifeisusedforwaterrinsingafterachemicalprocessorpre-treatingpriortoachemicalprocess（Figure3）.

Thefluidknifeconsiderablyreducesboththeconveyorlengthandthepowerrequiredtopumpsolutionontothepanel.Forexample,asinglefluidknifeprovidesasolutionrateof40Lperminuteusinga110Wpump,comparedtoamoreconventionalsprayrinsethatdelivers28Lperminutefroma750Wpump.Similarly,thefluidkniferequiresonly170mmofconveyorlengthcomparedto240mmforthesprayrinse.Aswiththefluidengine,thinmaterialtransportisassistedbythefluidflowcharacteristics,althoughtheproportionallylowerflowrateavoidstheneedfortheoverheadfluiddeflection,theupperoutflowbeingdeflectedtothesides.TheliquidthatescapestoeachsideofthepanelsisdeflecteddownwardusingtheCoandaeffectguidesonthebottomknifeandajetdeflectorontheexitoftheupperknife.Thisnegatestheneedforsegmentedcontainmentrollersorextendedentryandexitzones（Figure4）.

Figure3Fluidknifeshowingpassageofpanelthroughknifeandflowoffluid

Figure4Fluidknifeshowingfluidflowingtothesideofapanel

passingthroughtheknife

Jetknife

Thejetknifeprovidesmultipleupperandlowerhighimpingementconventionalsprayjetstodisplacesalts,fluxesandother“contaminants”thatarenotreadilydissolved.Theoffsetopposingjetsbalancematerialbetweentherollersandtheportedentryandexitguidesensurecontactlessentryandexittothesprayzone.Drainageholesinthelowerchamberensurethatfluidisdispersedquicklyanddoesnotfloodovertheisolationrollers.Thespacerequiredisthesameasforafluidknife,butitrequiresahigherpowerpump.ThejetknifecanbeseeninFigure5.

Figure5Jetknife

Dryingwithafluidknife

Basedontheknivesoriginallydevelopedandpatentedforhotairlevelling,thesesingleslotknivesareshapedsothatapressuredifferentialisproducedbetweentheupperandlowersurfacesofthepanel.Eachknifehasaseriesofslotscutintheleadingedgeseparatedbynarrowpanelguides.Thecutoutin

thelowerknifeisshapedsothatairleavingthelowerjetexpandsrapidlyproducingalow-pressureareabelowthepanel（Figure6）.

Figure6Dryingknife

Thislow-pressuredrawswaterfromtheholesbeforethepanelreachestheairjetanddirectsittothebottomofthedryingchamber.Theforcecreatedbythepressuredifferenceeithersideofthepanelalsostabilisesthepanel’spositioninrelationtothelowerknifeanditsintegralguidingsystem.Whendryingthickermaterial,problemscanbeencounteredwherewaterisleftonthetrailingedgeofthepanel.Althoughthewaterisremovedfromthesurfacebythejets,asmallamountremainsalongthetrailingverticalfaceofthepanel

andreturnstothehorizontalfaceoncethepanelisclearofthejets.Thethickerthepanel,themorewaterislikelytoremainthere.Afluidknifeincorporatingtheinclinedknifetechnique,describedinanearlierdryerpatent,cansuccessfullyremovewaterfromthetrailingedge.Inthisdesign,theairjetisinclinedacrossthewidthoftheconveyor.Waterisremovedfromthesurfaceanddrivenacrossthepanelandeffectively“wiped”offthetrailingfacebythejets.Eachparalleljetknifesetoccupiesthespaceofjusttworollerpitches.Owingtotheangleoftheslotusedintheinclinedjetknifeproducingawiderunitthisdesignoccupiesfourconveyorslots.Additionalspaceisneededtopreventpressurisationofprecedingchambersbytheairfromthejets,thisspacebeingfilledwithconveyorro