led

Introduction

Light-emittingdiodesarereferredtoasLEDsforshort.Itismadeofcompoundscontaininggallium(Ga),arsenic(As),phosphorus(P),nitrogen(N),etc.

Whenelectronsandholesrecombine,itcanradiatevisiblelight,soitcanbeusedtomakelight-emittingdiodes.Usedasindicatorlightincircuitsandinstruments,orcomposedoftextordigitaldisplay.Galliumarsenidediodesemitredlight,galliumphosphidediodesemitgreenlight,siliconcarbidediodesemityellowlight,andgalliumnitridediodesemitbluelight.Duetochemicalproperties,itisdividedintoorganiclight-emittingdiodeOLEDandinorganiclight-emittingdiodeLED.

Workingprinciple

Likeordinarydiodes,light-emittingdiodesarecomposedofaPNjunction,whichalsohasunidirectionalconductivity.Whentheforwardvoltageisappliedtothelight-emittingdiode,theholesinjectedfromthePareatotheNareaandtheelectronsinjectedfromtheNareatothePareaarerespectivelyincontactwiththeelectronsintheNareaandthevoidsinthePareawithinafewmicronsofthePNjunction.Theholesrecombineandproducespontaneousemissionfluorescence.Theenergystatesofelectronsandholesindifferentsemiconductormaterialsaredifferent.Whenelectronsandholesrecombine,theenergyreleasedissomewhatdifferent.Themoreenergyreleased,theshorterthewavelengthoftheemittedlight.Commonlyusedarediodesthatemitred,greenoryellowlight.Thereversebreakdownvoltageofthelight-emittingdiodeisgreaterthan5volts.Itsforwardvolt-amperecharacteristiccurveisverysteep,anditmustbeusedinserieswithacurrent-limitingresistortocontrolthecurrentthroughthediode.

Thecorepartofthelight-emittingdiodeisawafercomposedofP-typesemiconductorandN-typesemiconductor.ThereisatransitionlayerbetweenP-typesemiconductorandN-typesemiconductor,whichiscalledPNjunction.InthePNjunctionofcertainsemiconductormaterials,whentheinjectedminoritycarriersandthemajoritycarriersrecombine,theexcessenergyisreleasedintheformoflight,therebydirectlyconvertingelectricalenergyintolightenergy.WithreversevoltageappliedtothePNjunction,itisdifficulttoinjectminoritycarriers,soitdoesnotemitlight.Whenitisinapositiveworkingstate(thatis,apositivevoltageisappliedtobothends),whenthecurrentflowsfromtheLEDanodetothecathode,thesemiconductorcrystalemitslightofdifferentcolorsfromultraviolettoinfrared.Theintensityofthelightisrelatedtothecurrent.

Thefollowingaretheinorganicsemiconductormaterialsusedintraditionallight-emittingdiodesandthecolorstheyemit

FeaturesofLEDlights

LEDlightsarelight-emittingdiodesthatusesolidsemiconductorsThechipisaluminescentmaterial.Comparedwithtraditionallamps,LEDlampsareenergy-saving,environmentallyfriendly,andhavegoodcolorrenderingandresponsespeed.

(1)EnergysavingisthemostprominentfeatureofLEDlamps

Intermsofenergyconsumption,theenergyconsumptionofLEDlampsisone-tenthofthatofincandescentlampsandaquarterofthatofenergy-savinglamps.one.ThisisoneofthebiggestfeaturesofLEDlights.Peoplenowadaysadvocateenergysavingandenvironmentalprotection.ItispreciselybecauseofthisfeatureofenergysavingthattheapplicationrangeofLEDlightsisverywide,makingLEDlightsverypopular.

(2)Itcanworkinhigh-speedswitchingmode

Weusuallywalkontheroad,andwewillfindthateveryLEDscreenorpictureisunpredictable.ThisshowsthatLEDlightscanbeswitchedonandoffathighspeed.However,fortheincandescentlampsweusuallyuse,itcannotachievesuchaworkingstate.Innormallife,iftheswitchisswitchedtoomanytimes,itwilldirectlycausethefilamentoftheincandescentlamptobreak.ThisisalsoanimportantreasonforthepopularityofLEDlights.

(3)Environmentalprotection

TheLEDlampdoesnotcontainanyheavymetalmaterialssuchasmercury,buttheincandescentlampcontainsit,whichreflectstheenvironmentalprotectioncharacteristicsoftheLEDlamp.Nowadays,peopleattachgreatimportancetoenvironmentalprotection,somorepeoplearewillingtochooseenvironmentallyfriendlyLEDlights.

(4)Fastresponsespeed

AnoutstandingfeatureofLEDlightsisthattheresponsespeedisrelativelyfast.Assoonasthepoweristurnedon,theLEDlightwilllightupimmediately.Comparedwiththeenergy-savinglampsweusuallyuse,theresponsespeedisfaster.Whenthetraditionallightbulbisturnedon,itoftentakesalongtimetoilluminatetheroom,anditcanonlylightupafterthelightbulbhascompletelyheatedup.

(5)Comparedwithotherlightsources,LEDlightsaremore"clean"

Theso-called"clean"doesnotrefertothecleansurfaceandinteriorofthelamp,butthelampisThecoldlightsourcedoesnotgeneratetoomuchheatandwillnotattractinsectsthatlikelightandheat.Especiallyinsummer,therewillbealotofbugsinthecountryside.

Someinsectsloveheatbynature.Incandescentlampsandenergy-savinglampswillgenerateheatafteraperiodofuse.Thisheathappenstobelikedbyinsects,anditiseasytoattractinsects.Thiswillundoubtedlybringalotofpollutantstothesurfaceofthelamp,andtheexcrementofinsectswillmaketheroomverydirty.However,theLEDlampisacoldlightsourceandwillnotattractinsects,sothatnoinsectexcrementwillbeproduced.Therefore,LEDlightsaremore"clean".

Relatedparameters

TheimportantaspectsoftheopticalparametersofLEDsare:luminousflux,luminousefficiency,luminousintensity,luminousintensitydistribution,andwavelength.

Luminousefficiencyandluminousflux

Luminousefficiencyistheratioofluminousfluxtoelectricpower,andtheunitisgenerallylm/W.Luminousefficiencyrepresentstheenergy-savingcharacteristicsofthelightsource,whichisanimportantindicatortomeasuretheperformanceofmodernlightsources.

Luminousintensityandluminousintensitydistribution

LEDluminousintensityisacharacterizationofitsluminousintensityinacertaindirection,becausetheLEDisindifferentspatialanglesThereisalotofdifferenceinlightintensity,andthenwestudiedthelightintensitydistributioncharacteristicsofLEDs.ThisparameterisofgreatpracticalsignificanceanddirectlyaffectstheminimumviewingangleoftheLEDdisplaydevice.Forexample,large-scalecolorLEDdisplayscreensinstadiums,iftheselectedLEDsingletubedistributionrangeisverynarrow,thentheaudiencefacingthedisplayscreenatalargeranglewillseeadistortedimage.Moreover,thetrafficsignlightsalsorequirealargerrangeofpeopletobeabletorecognize.

Wavelength

ForthespectralcharacteristicsoftheLED,wemainlyseewhetheritsmonochromaticityisgood,andwemustpayattentiontored,yellow,blue,green,WhetherthemaincolorssuchaswhiteLEDarepure.Becauseinmanyoccasions,suchastrafficsignallights,thecolorrequirementsaremorestringent.However,itisobservedthatsomeoftheLEDsignallightsinourcountryareblueingreenanddeepredinred.Fromthisphenomenon,wehaveconductedspecialresearchonthespectralcharacteristicsofLEDs.Verynecessaryandverymeaningful.

Mainclassification

Light-emittingdiodescanalsobedividedintoordinarymonochromaticlight-emittingdiodes,high-brightnesslight-emittingdiodes,ultra-high-brightnesslight-emittingdiodes,color-changinglight-emittingdiodes,flashinglight-emittingdiodes,voltagecontroltypeLight-emittingdiodes,infraredlight-emittingdiodesandnegativeresistancelight-emittingdiodes,etc.

ThecontrolmodeofLEDhastwokindsofconstantcurrentandconstantvoltage.Therearemultipledimmingmethods,suchasanalogdimmingandPWMdimming.MostoftheLEDsarecontrolledbyconstantcurrent,whichcanmaintainThestabilityoftheLEDcurrentisnotsusceptibletothechangeofVF,whichcanprolongtheservicelifeoftheLEDlamp.

MonochromaticLED

OrdinarymonochromaticLED

OrdinarymonochromaticLEDhassmallsize,lowworkingvoltage,Ithastheadvantagesoflowworkingcurrent,uniformandstableluminescence,fastresponsespeed,longlife,etc.ItcanbedrivenbyvariousDC,AC,pulseandotherpowersourcestolightup.Itisacurrent-controlledsemiconductordevice,andsuitablecurrent-limitingresistorsneedtobeconnectedinserieswhenused.

Thelight-emittingcolorofordinarymonochromaticlight-emittingdiodesisrelatedtothelight-emittingwavelength,andthelight-emittingwavelengthdependsonthesemiconductormaterialusedtomanufacturethelight-emittingdiode.Thewavelengthofredlight-emittingdiodesisgenerally650-700nm,thewavelengthofamberlight-emittingdiodesisgenerally630-650nm,thewavelengthoforangelight-emittingdiodesisgenerallyabout610-630nm,thewavelengthofyellowlight-emittingdiodesisgenerallyabout585nm,andthewavelengthofgreenlight-emittingdiodesGenerally,itis555~570nm.

High-brightnessmonochromaticlight-emittingdiodes

High-brightnessmonochromaticlight-emittingdiodesandultra-high-brightnessmonochromaticlight-emittingdiodesusesemiconductormaterialsandordinarymonochromaticlightThediodeisdifferent,sotheintensityofthelightisalsodifferent.Generally,high-brightnessmonochromaticlight-emittingdiodesusegalliumaluminumarsenide(GaAlAs)andothermaterials,ultra-high-brightnessmonochromaticlight-emittingdiodesusematerialssuchasgalliumindiumarsenide(GaAsInP),andordinarymonochromaticlight-emittingdiodesusegalliumphosphide(GaP).)Orgalliumarsenidephosphorous(GaAsP)andothermaterials.

Color-changinglight-emittingdiodes

Color-changinglight-emittingdiodesarelight-emittingdiodesthatcanchangethecoloroflight.Color-changinglight-emittingdiodescanbedividedintotwo-colorlight-emittingdiodes,three-colorlight-emittingdiodesandmulti-color(red,blue,green,andwhite)light-emittingdiodes.

Thecolor-changinglight-emittingdiodescanbedividedintotwo-terminalcolor-changinglight-emittingdiodes,three-terminalcolor-changinglight-emittingdiodes,four-terminalcolor-changinglight-emittingdiodesandsix-terminalcolor-changinglight-emittingdiodesaccordingtothenumberofpins.

Blinkinglight-emittingdiode

Blinkinglight-emittingdiode(BTS)isaspeciallight-emittingdevicecomposedofCMOSintegratedcircuitsandlight-emittingdiodes,whichcanbeusedforalarmindicationandundervoltageandovervoltageindication.

Whentheflashinglight-emittingdiodeisinuse,thereisnoneedtoconnectothercomponents,aslongasanappropriateDCworkingvoltage(5V)isaddedtobothendsofitspin,itcanflashandemitlight.

Infraredlightemittingdiode

Infraredlightemittingdiodeisalsocalledinfraredemittingdiode.Itisalightemittingdevicethatcandirectlyconvertelectricalenergyintoinfraredlight(invisiblelight)andradiateout.ItsmainapplicationInallkindsoflightcontrolandremotecontroltransmittingcircuits.

Thestructureandprincipleofinfraredlight-emittingdiodesaresimilartothoseofordinarylight-emittingdiodes,exceptthatthesemiconductormaterialsusedaredifferent.Infraredlight-emittingdiodesusuallyusegalliumarsenide(GaAs),galliumaluminumarsenide(GaAlAs)andothermaterials,andarepackagedinfullytransparentorlightblue,blackresin.

Thecommonlyusedinfraredlight-emittingdiodesincludeSIRseries,SIMseries,PLTseries,GLseries,HIRseriesandHGseries.

Ultravioletlight-emittingdiodes

Ultravioletlight-emittingdiodes(UVLEDs)basedonsemiconductormaterialshavetheadvantagesofenergysaving,environmentalprotectionandlonglife,andareimportantinthefieldsofsterilizationanddisinfection,medicaltreatmentandbiochemicaltesting.Applicationvalue.Inrecentyears,semiconductorUVoptoelectronicmaterialsanddeviceshaveattractedmoreandmoreattentionaroundtheworldandhavebecomearesearchanddevelopmenthotspot.OnDecember9-12,2018,thethird"InternationalSymposiumonUltravioletMaterialsandDevices"(IWUMD-2018)hostedbytheInstituteofSemiconductorsoftheChineseAcademyofScienceswasheldinKunming,Yunnan.Morethan270representativesfrom12countriesattendedThemeeting.Thisconferencebroughttogetherthelatestresearchanddevelopmentresultsreportsofmanytopexpertsathomeandabroadintherelatedfieldsofultravioletlight-emittingdiodematerialsanddevices.

Currently,ultravioletlight-emittingdiodesarethemaintrendinthedevelopmentofnitridetechnologyandthedevelopmentofthird-generationsemiconductormaterialtechnology,andhavebroadapplicationprospects.Inordertospeedupthedevelopmentofthethird-generationsemiconductorsolid-stateultravioletlightsource,theMinistryofScienceandTechnologyofChinaisstrivingtoimplementthespecialkeyresearchanddevelopmentplanofthe"third-generationsemiconductorsolid-stateultravioletlightsourcematerialanddevicekeytechnology"(2016YFB0400800).ThesupportofthenationalkeyresearchanddevelopmentplanandtheholdingoftheInternationalUVMaterialsandDevicesSeminarwillacceleratetherealizationofthemarketapplicationofmycountry’sthird-generationsemiconductorUVlightsources,anddrivethedevelopmentofmycountry’sUVsemiconductorlight-emittingdiodematerialsanddevicetechnologiestocreateaffinityandindustrialization.positiveeffect.

OrganicLight-EmittingDiodes

In1987,KodakCompanyDengQingyunandotherssuccessfullypreparedlow-voltage,high-brightnessorganiclight-emittingdiodes(OLED),showingtheworld'sfirstCommercialapplicationprospects'".In1995,Kidopublishedanarticleonwhitelightorganiclight-emittingdiodes(wOLED)inSciencemagazine.Althoughitisnotefficient,itopenedthepreludetoOLEDlightingresearch.Afterdecadesofdevelopment,Atpresent,theefficiencyandstabilityofOLEDhavealreadymettherequirementsofsmall-sizedisplays,andithasbeenfavoredbymanyhigh-endinstrumentation,mobilephoneandmobileterminalcompanies,andlarge-sizetechnologyisgraduallyimproving.

ThedevelopmentofOLEDmaterialsistheOLEDindustryThebasisforvigorousdevelopment.TheearliestOLEDlight-emittingmaterialsarefluorescentmaterials,butduetospininhibition,theupperlimitofthetheoreticalinternalquantumefficiencyoffluorescentmaterialscanonlyreach25%.In1998,MaandForrestandThompsonsuccessivelyreportedtheuseofphosphorescentmaterials.TheapplicationofOLEDmaterialshasopenedthewayforbreakingthelawofspinstatisticsandusing100%oftheenergyofallexcitons.However,phosphorescentmaterialsalsohavecertainproblems,becausetheycontainpreciousmetals,thepriceishigh,andthebluelightmaterialshavelong-termstabilityStagnant.

In2009,ProfessorAdachiofKyushuUniversityinJapanintroducedthermallyactivateddelayedfluorescence(TADF)materialsintoOLEDsforthefirsttime.Suchmaterialshaveextremelylowsingletripletenergygapsandcanpasstripletstates.Thereverseintersystemcrossingofexcitons(RISC)achievesatheoreticalinternalquantumefficiencyof100%.Thematerialsystemanddevicestructurearebecomingmoreandmoreperfect,makingOLEDsstandoutinthedisplayfield.Ontheotherhand,WOLEDshavehighluminousefficiencyandadjustablespectrum.Aseriesofadvantagessuchaslowbluelightcomponentandsurfacelightsource.Asahigh-efficiencylightsourcewithlowcolortemperatureandnobluehazard,itisexpectedtobecomeanewtrendofhealthylightinginthefuture.

Production

Materialsh3>

ThefivemajorrawmaterialsofLEDare:chip,bracket,silverglue,goldwire,epoxyresin

chip

Composition:Itiscomposedofgoldpad,Ppole,Npole,PNjunction,andbackgoldlayer(doublepadwaferwithoutbackgoldlayer).ThewaferiscomposedofP-layersemiconductorelements,andN-layersemiconductorelementsarerearrangedandcombinedbythemovementofelectrons.PNcombination.Itisthischangethatenablesthewafertobeinarelativelystablestate.Whenthewaferisappliedwithacertainvoltagetotheforwardelectrode,theholesintheforwardPareawillcontinuouslyswimtotheNarea.TheelectronsintheareawillmoverelativetotheholestotheParea.Whiletheelectronsandholesmoverelativetoeachother,theelectronsandholespairwitheachothertoexcitephotonsandgeneratelightenergy.

Mainclassification,surfaceemittingtype:Mostofthelightisemittedfromthesurfaceofthechip.Five-sidedluminoustype:Therearemorelightemittedonthesurfaceandsidesaccordingtotheluminouscolor,red,orange,yellow,yellow-green,puregreen,standardgreen,blue-green,andblue.

Stent

Thestructureofthestentis1layerofiron,2layersofcopperplating(goodelectricalconductivity,fastheatdissipation),3layersofnickelplating(anti-oxidation),4Silver-platedlayer(goodreflectivity,easytowire)

Silverglue(duetomoretypes,wetakeH20Easanexample)

AlsocalledwhiteGlue,milkywhite,conductiveadhesion(bakingtemperature:100°C/1.5H)silverpowder(conductive,heatdissipation,fixedchip)+epoxyresin(curedsilverpowder)+thinner(easytostir).Storageconditions:Silvergluemanufacturersgenerallystoresilverglueat-40°C,andapplicationunitsgenerallystoresilverglueat-5°C.Singleagentis25°C/1year(inadryandventilatedplace),mixedagentis25°C/72hours(butduetootherfactors"temperature,humidity,andventilationconditions"duringonlineoperation,toensurethequalityoftheproductisaverageTheusetimeofthemixtureis4hours)

Bakingconditions:150°C/1.5H

Stirringconditions:Stirringinonedirectionfor15minutes

Goldwire(takeφ1.0milasanexample)

ThegoldwireusedbyLEDisφ1.0mil,φ1.2mil,thematerialofgoldwire,andthematerialofgoldwireforLEDGenerally,thegoldcontentis99.9%.Theuseofgoldwire

Usingitshighgoldcontent,softmaterial,easytodeform,goodelectricalconductivity,andgoodheatdissipationcharacteristics,aclosedcircuitisformedbetweenthechipandthesupport.(Conversionrelationship:1mil=0.0254mm,1in=25.4mm)

Epoxyresin(takeEP400asanexample)

Composition:A,Btwocomponents:

Aglue:isthemainagent,composedofepoxyresin+defoamer+heat-resistantagent+diluent

Bagent:isacuringagent,composedofAcidic+releaseagent+accelerator

Conditionsofuse:

Mixingratio:A/B=100/100(weightratio)

Mixedviscosity:500-700CPS/30°C

Geltime:120°C*12minutesor110°C*18minutes

Availableconditions:roomtemperature25°Cabout6hours.Generally,accordingtotheproductionneedsoftheproductionline,wesetitsuseconditionas2hours.

Curingconditions:Initialcuringat110°C—140°Cfor25-40minutes

Latercuringat100°C*6-10hours(flexibilityadjustmentscanbemadeaccordingtoactualneeds)

Process

Chipinspection

Microscopicinspection:Whethertherearemechanicaldamagesandpitsonthesurfaceofthematerial,lockhillchipsizeandelectrodeWhetherthesizemeetstheprocessrequirementsandwhethertheelectrodepatterniscomplete.

LEDexpansion

BecausetheLEDchipsarestillarrangedtightlyafterdicing,thespacingisverysmall(about0.1mm),whichisnotconducivetotheoperationofthesubsequentprocess.Thefilmexpandingmachineisusedtoexpandthefilmofthebondingchip,sothatthedistancebetweentheLEDchipsisstretchedtoabout0.6mm.Manualexpansioncanalsobeused,butitiseasytocauseundesirableproblemssuchaschipdropandwaste.

LEDdispensing

PutsilverglueorinsulatingglueonthecorrespondingpositionoftheLEDbracket.ForGaAs,SiCconductivesubstrates,red,yellow,andyellow-greenchipswithbackelectrodes,silverglueisused.ForblueandgreenLEDchipswithsapphireinsulatingsubstrates,insulatingglueisusedtofixthechips.

Thedifficultyoftheprocessliesinthecontroloftheamountofglue.Therearedetailedtechnologicalrequirementsfortheheightofthecolloidandthepositionoftheglue.Sincesilverglueandinsulatinggluehavestrictrequirementsforstorageanduse,remind:thewaking,mixing,andusetimeofsilvergluearemattersthatmustbepaidattentiontointheprocess.

LEDgluepreparation

Incontrasttodispensing,gluepreparationistouseagluepreparationmachinetofirstcoatthesilverglueonthebackelectrodeoftheLED,andthenapplythebackTheLEDwithsilverglueisinstalledontheLEDbracket.Theefficiencyofgluepreparationismuchhigherthanthatofgluedispensing,butnotallproductsaresuitableforthegluepreparationprocess.

LEDmanualpiercingpiece

PlacetheexpandedLEDchip(withorwithoutglue)onthefixtureofthepiercingpiecetable,andplacetheLEDbracketUnderthefixture,useaneedletopiercetheLEDchipstothecorrespondingpositionsonebyoneunderthemicroscope.Comparedwithautomaticrackmounting,manualpiercingpiecehasanadvantage,itisconvenienttochangedifferentchipsatanytime,anditissuitableforproductsthatneedtoinstallmultiplechips.

AutomaticLEDmounting

Automaticmountingisactuallyacombinationofthetwostepsofglue(dispensing)andchipmounting,firstontheLEDbracketPutonthesilverglue(insulatingglue),andthenusethevacuumsuctionnozzletosuckupthemovingpositionoftheLEDchip,andthenplaceitonthecorrespondingbracketposition.Intheprocessofautomaticracking,itismainlynecessarytobefamiliarwiththeequipmentoperationprogramming,andatthesametimeadjusttheglueandinstallationaccuracyoftheequipment.Intheselectionofnozzles,bakelitenozzlesshouldbeusedasmuchaspossibletopreventdamagetothesurfaceoftheLEDchip,especiallybakelitemustbeusedforblueandgreenchips.Becausethesteelnozzlewillscratchthecurrentdiffusionlayeronthesurfaceofthechip.

LEDsintering

Thepurposeofsinteringistocurethesilverpaste.Thesinteringrequirestemperaturemonitoringtopreventpoorbatchperformance.Thesinteringtemperatureofsilverpasteisgenerallycontrolledat150°C,andthesinteringtimeis2hours.Accordingtotheactualsituation,itcanbeadjustedto170°Cfor1hour.Insulatingglueisgenerally150°Cfor1hour.

Thesilvergluesinteringovenmustbeopenedevery2hours(or1hour)accordingtotheprocessrequirementstoreplacethesinteredproducts,andnotopenatwill.Thesinteringovenmustnotbeusedforotherpurposestopreventpollution.

LEDpressurewelding

ThepurposeofpressureweldingistoleadtheelectrodetotheLEDchiptocompletetheconnectionoftheinnerandouterleadsoftheproduct.

ThebondingprocessofLEDhastwotypes:goldwireballbondingandaluminumwirebonding.TheprocessofaluminumwirebondingistofirstpressthefirstpointontheelectrodeoftheLEDchip,thenpullthealuminumwireontothecorrespondingbracket,pressthesecondpointandthentearthealuminumwire.Thegoldwireballbondingprocessburnsaballbeforepressingthefirstpoint,andtherestoftheprocessissimilar.

Press-weldingisakeylinkinLEDpackagingtechnology.Themainthingsthatneedtobemonitoredintheprocessaretheshapeofthepressure-weldedgoldwire(aluminumwire),theshapeofthesolderjoint,andthetensileforce.

LEDencapsulation

LEDencapsulationismainlyglued,potted,andmolded.Basically,thedifficultiesofprocesscontrolarebubbles,lackofmaterial,andblackspots.Thedesignismainlytheselectionofmaterials,andthechoiceofepoxyandbracketsthatarewell-combined.(GeneralLEDcannotpasstheairtightnesstest).

LEDdispensingTOP-LEDandSide-LEDaresuitablefordispensingpackaging.Manualdispensingpackagingrequireshighlevelsofoperation(especiallywhiteLEDs).Themaindifficultyisthecontrolofthedispensingvolume,becausetheepoxywillthickenduringuse.DispensingforwhitelightLEDsalsohastheproblemofphosphorprecipitationcausingcolordifferenceinlightoutput.

LEDpottingpackageLamp-LEDpackageadoptspottingform.ThepottingprocessistofirstinjectliquidepoxyintotheLEDmoldingcavity,theninsertthepressure-weldedLEDbracket,putitintotheoventocuretheepoxy,andthentaketheLEDoutofthecavitytoform.

LEDmoldingpackagePutthepressure-weldedLEDbracketintothemold,clamptheupperandlowermoldswithahydraulicpressandvacuum,andputthesolidepoxyintotheentranceoftheinjectionchannelandusethehydraulicjackforheating.Therodispressedintothemoldgluechannel,andtheepoxyfollowsthegluechannelintoeachLEDmoldinggrooveandcures.

LEDcuringandpost-curing

Curingreferstothecuringofencapsulatedepoxy.Thegeneralepoxycuringconditionsareat135°Cfor1hour.Moldedpackagesaregenerallyat150°Cfor4minutes.Thepost-curingistofullycuretheepoxywhilethermallyagingtheLED.Post-curingisveryimportanttoimprovethebondingstrengthbetweenepoxyandPCB.Thegeneralconditionsare120°C,4hours.

LEDcuttinganddicing

BecausetheLEDsareconnectedtogetherinproduction(notasingle),LamppackagedLEDsusecuttingribstocuttheLEDTheconnectingbarsofthebracket.SMD-LEDisonaPCBboardandrequiresadicingmachinetocompletetheseparationwork.

LEDtest

TestthephotoelectricparametersoftheLED,inspecttheappearancesize,andsorttheLEDproductsaccordingtocustomerrequirements.

Application

Inthe1990s,LEDtechnologymadegreatprogress.Notonlydidtheluminousefficiencysurpassincandescentlamps,thelightintensityreachedthecandlelightlevel,andthecolorsalsocoveredfromredtoblue.Theentirevisiblespectralrange.Thistechnologicalrevolutionfromindicatorleveltobeyondthelevelofgenerallightsourceshasledtoavarietyofnewapplications,suchascarsignallights,trafficlights,largeoutdoorfull-colordisplayscreens,andspeciallightingsources.

Withthedevelopmentofhigh-brightnessandmulti-colorlight-emittingdiodes,theapplicationfieldisalsoexpanding.Fromthelowerluminousfluxindicatortothedisplayscreen,andthenfromtheoutdoordisplaytothemediumluminousfluxpowersignallampandThewhitelightsourceforspeciallightingfinallydevelopedtothehigh-luminousfluxgenerallightingsourceintheupperrightcorner.Theyear2000isthedividinglineoftime.In2000,thesignaldisplayproblemsandlightingproblemsofallcolorshavebeensolved,andspeciallightingapplicationswithlowandmediumluminousfluxeshavebegun.However,asgenerallightingapplicationsforhighluminousfluxwhitelightlighting,itseemsthatthereisstilltime.InJapan,theluminousfluxneedstobefurtherincreasedsignificantlybeforeitcanberealized.Ofcourse,thisisalsoaprocess,whichwillbegraduallyrealizedasthebrightnessincreasesandthepricedecreases.

LEDdisplayscreen

Sincethemid-1980s,therehavebeenmonochromeandmulti-colordisplayscreens,initiallytextscreensoranimatedscreens.Intheearly1990s,thedevelopmentofelectroniccomputertechnologyandintegratedcircuittechnologyenabledtherealizationofthevideotechnologyofLEDdisplayscreens.TVimagesweredirectlyonthescreen.Especiallyinthemid-1990s,blueandgreenultra-highbrightnessLEDsweresuccessfullydevelopedandputintoproductionquickly.Greatlyexpandtheapplicationofoutdoorscreens,withanarearangingfrom100to300m.

Currently,LEDdisplaysarewidelyusedinstadiums,squares,venues,andevenstreetsandshoppingmalls.TheNasdaqfull-colorscreenonTimesSquareintheUnitedStatesisthemostfamous,withanareaof​​120feet×90feet,Equivalentto1005m,madeof19millionultra-brightblue,greenandredLEDs.Inaddition,securitiesmarketscreens,bankexchangeratescreens,andinterestratescreensalsoaccountforalargeproportionofapplications.Recently,therehasalsobeenalargedevelopmentininformationscreensonexpresswaysandelevatedroads.Theapplicationoflight-emittingdiodesinthisfieldhasbecomeascale,forminganewindustry,andarelativelystablegrowthcanbeexpected.

Trafficsignallights

ThenavigationlightshaveusedLEDsasthelightsourceformanyyears.Thecurrentworkistoimproveandperfect.Roadtrafficsignallightshavemadegreatprogressinrecentyears,withrapidtechnologicaldevelopmentandrapidapplicationdevelopment.Chinacurrentlyhasabout40,000setsofordersperyear,whileCaliforniaintheUnitedStatesreplaced50,000setsoftraditionalLEDtrafficlightsinthepastyear.Accordingtotheuseeffect,thesignallampofthelightsourcehasalonglife,powersavingandmaintenance-freeeffect.ThecurrentpeakwavelengthsofLEDsusedarered630nm,yellow590nm,andgreen505nm.Itshouldbenotedthatthedrivingcurrentshouldnotbetoolarge,otherwisethehightemperatureconditionsunderthesummersunwillaffectthelifeoftheLED.

Recently,LEDairport-specificsignallightsusedinairportsasbeacons,floodlightsandomnidirectionallightshavealsobeensuccessfulandputintouse,andtheresultshavebeenverygoodinmanyways.Ithasindependentintellectualpropertyrightsandhasobtainedtwopatents.Ithasgoodreliability,energysaving,maintenance-free,andcanbepromotedandappliedtovariousairports.Itcanreplaceoldsignallightsthathavebeenusedfordecades.Itnotonlyhashighbrightness,butalsobecauseofthepurityofLEDlightcolorGood,veryclear,easytoidentifythesignal.

Carlights

Ultra-brightLEDcanbemadeintocarbrakelights,taillightsanddirectionlights,andcanalsobeusedforinstrumentlightingandinteriorlighting.Itisresistanttovibrationandsavesenergy.Ithasobviousadvantagesoverincandescentlampsintermsofelectricityandlonglife.Usedasabrakelight,itsresponsetimeis60ns,whichismuchshorterthanthe140msofanincandescentlamp.Drivingonatypicalhighwaywillincreasethesafetydistanceof4-6m.

LCDbacklightsource

LEDasthebacklightsourceofliquidcrystaldisplay,itcannotonlybeusedasgreen,red,blue,white,butalsoasacolor-changingbacklight.TherearemanyproductsEntertheproductionandapplicationstage.Recently,theLCDscreenonthemobilephoneismadeofLEDbacklight,whichhasimprovedthequalityoftheproduct,andtheeffectisverygood.A15-inch(1inch≈2.5cm)LCDscreenbacklightmadeof8blue,24green,and32redLuxeonLEDscanreach120W,2500lm,andbrightness18000nits(nits,cd/m²).22LCDscreenbacklighthasalsobeenmade,only6mmthick,notonlyhasagoodcolormixingeffect,butalsohasacolorrenderingindexofmorethan80.Althoughlarge-scalebacklightsourcesarecurrentlyinthedevelopmentstage,theyhavegreatpotential.

Lighting

Duetotheincreaseinthebrightnessoflight-emittingdiodesandthedecreaseinprice,coupledwithlonglifeandpowersaving,itiseasiertodriveandcontrolthanneonlights.Itcannotonlyflicker,butalsochangecolor.Therefore,monochromatic,multi-colorandevencolor-changinglight-emittingcolumnsmadeofultra-high-brightnessLEDsareequippedwithlight-emittingunitsofothershapestodecoratelandscapeprojectssuchastallbuildings,bridges,streetsandsquares.Asceneoftwinklingstarsandcolorfulstreamers.ManycompanieshaveproducedLEDlightbeamsofmorethan10,000metersandtensofthousandsofcoloredlights.Theyarecurrentlybeinggraduallypromoted,anditisestimatedthattheywillgraduallyexpandtoformasingleindustry.

Lightingsource

TheLEDlightsourceusedasthelightingsourceshouldbewhitelight.Atpresent,asmilitarywhitelightLEDlightingfixtures,somevarietieshavebeenputintomassproduction.SincetheLEDlightsourcehasnoinfraredradiation,itiseasytoconceal,anditalsohastheadvantagesofvibrationresistance,suitableforbatterypowersupply,solidstructureandconvenientcarrying,etc.,therewillbegreaterdevelopmentinspeciallightingsources.Lawnlampsandundergroundlampsforcivilianusehavebeenproducedonalargescale.Theyarealsousedasmicroscopefieldlighting,flashlights,surgeons'headlights,museumsorartexhibitions,andreadinglamps.

Greenhousesupplementlight

Lightisoneofthemostimportantenvironmentalfactorsforplantgrowthanddevelopment,andithaseffectsonplantgrowth,morphogenesis,photosynthesis,materialmetabolismandgeneexpression.Therefore,thegreenhouselightsupplementisanimportantwaytoachievehigh-qualityandhigh-yieldplants.Inrecentyears,theapplicationoflight-emittingdiodesinplantfactorieshasbecomemoreandmoreextensive.TheadvantagesofLEDlightsource'snarrowwavewidth,lowenergyconsumption,smallsize,highefficiency,agingresistance,andlowheatconsumptionhavemadeitalotoflightqualityresearchers.Newlightsourceused.Sofar,alargenumberofLEDlightsourceshavebeenusedtostudytheeffectsoflightenvironmentonthemacroscopicmorphology,yield,andqualityofplants,aswellastheeffectsoncellmicrostructure,plantdifferentiation,andsecondarymetabolites.

Heatdissipationofthelight-emittingdiodepackage

Insemiconductorlightingdevices,high-powerandhigh-brightnesslight-emittingdiodes(LEDs)areusuallyusedaslightsources.Whencurrentispassedthroughthelight-emittingdiodes,Electronsandholeswilldirectlyrecombine,therebyreleasingenergytoemitlight.Ithastheadvantagesoflowpowerconsumptionandlongservicelife,andiswidelyusedinthefieldoflighting.However,thecurrentphotoelectricconversionefficiencyislow,andalargeproportionisconvertedintoheatenergy,sothepowerdensityontheLEDchipishigh.Thehighpowerdensityalsoputsforwardhighrequirementsontheheatdissipationofthedevice,andtheheatdissipationproblemofthepackageinthelightemittingdiodehasbecomeamajorproblemaffectingitsindustrialdevelopment.

Coolingmethodofheatdissipation

TheheatdissipationmechanismofLEDgenerallyhastheseseveralforms:

1.TheuseofthermallyconductivemetalorheatdissipationfinsandtheLEDpackagetoattachheatdissipation.

2.Installafantoforceheatdissipation.

3.Acirculatingliquidisprovidedinthepackagetodissipateheat.

4.Thecombinationoftheheatpipeinthepackagecanabsorbordissipateheatenergywhentheworkingmediumintheheatpipechangesphase.

Principlesandfeatures

Heatpipesusetheprincipleofphasechangeforheatdissipation,andhavethecharacteristicsofabsorbingordissipatinghighheatenergy,whichmakestheheatpipeadevicewithextremelyhighheatconductionefficiency.Coolingmainlyusestheevaporationandcondensationoftheworkingfluidinavacuumtotransferheat.Whenoneendoftheheatpipeisheated,theworkingliquidinthecapillarywickevaporatesandvaporizes,andthesteamflowstotheotherendunderthepressuredifferencetoreleaseheatandcondenseintoaliquid.Thentheporousmaterialflowsbacktotheevaporationendbycapillaryaction,andtheheatcanbequicklytransferredalongtheheatpipe.

Perovskitelight-emittingdiodes

TraditionalinorganicLEDtechnologyisrelativelymatureandhashighluminousefficiency.Itiswidelyusedinthefieldoflighting,butthepreparationprocesssuchasepitaxialgrowthrestrictsitsdifficultyinlargeareasAndflexibledevicepreparation.OrganicorquantumdotLEDshaveadvantagessuchaseasyfilmformationonalargeareaandflexibility,buttheproblemsoflowefficiencyandshortlifeunderhighbrightnessstillneedtobesolvedurgently.Metalhalideperovskite-typematerialshavemanyadvantagesofbothinorganicandorganicmaterials."Suchaslargeareapreparationbysolutionmethod,adjustablebandgap,highcarriermobility,andhighfluorescenceefficiency.Therefore,basedonperovskitematerialsComparedwithtraditionallight-emittingdiodes,theLEDhasmanyadvantages,especiallylow-cost,large-areapreparationofhigh-brightness,high-efficiencylight-emittingdevices,whichisofgreatsignificancefordisplayandlighting.

Perovskitelight-emittingdiodesThedevelopmentisrapid.SinceCambridgeUniversityreportedthefirstthree-dimensionalperovskitelight-emittingdevicewithanexternalquantumefficiency(EQE)of0.76%in2014,afterjustfiveyearsofdevelopment,near-infrared,redandgreenlight-emittingperovskitelight-emittingdevicesTheexternalquantumefficienciesofallofthemhaveexceeded20%.ItisworthmentioningthatChinesescientistshavepioneerednewresearchmethodsinmanydirectionsinthefieldofperovskiteluminescence.

In2015,NanjingUniversityofTechnologyandZhejiangTheuniversityteamcooperatedtoreporttheperovskitelight-emittingdiodewithanexternalquantumefficiencyof3.5%,whichwasthehighestrecordatthetimeandthefirstdomesticpaperinthisfield.Subsequently,BeijingInstituteofTechnologyandNanjingUniversityofScienceandTechnologysuccessivelyreportedonquantumdot-basedPerovskiteLED.In2016,NanjingUniversityofTechnologyusedperovskitewithamulti-quantumwellstructuretoachieveanear-infraredperovskiteLEDwithanexternalquantumefficiencyofover10%.Therelatedresultswerepublishedin"NaturePhotonics"in2016.AdoptedInasimilarway,theInstituteofSemiconductorsoftheChineseAcademyofSciencesincreasedtheexternalquantumefficiencyofthegreenperovskiteLEDto14.36%.In2018,NanjingUniversityofTechnologyincreasedtheexternalquantumefficiencyofthenear-infraredperovskiteLEDto20.7%forthefirsttime,whichiscomparabletotheperformanceofindustrialization.OrganicandquantumLEDs.Inthesameyear,HuaqiaoUniversity’sStateraisedtheEQEofgreenperovskiteLEDsto20.3%.

Thesetwodomesticachievementswerecommentedbyfieldexpertsinvitedby"Nature"as"breakthroughachievements","amilestoneintheapplicationofperovskitematerialsinlight-emittingdiodes",and"makeperovskiteLEDtechnologybreaksthroughperformancebarriersandwillpromotetheindustrialdevelopmentofperovskiteLEDs."Generallyspeaking,ChinaiscurrentlytheworldleaderinperovskiteLEDresearch,especiallyinhigh-brightness,high-stabilityperovskitelight-emittingdevices,hasobtainedindependentintellectualpropertyrights.Innovativeachievementswithworldinfluence.

AlthoughtheresearchofperovskiteLEDhasmadegreatprogress,itsdevelopmentstillfacesmanychallenges.Firstofall,thestabilityproblemoftheperovskiteLEDneedstobesolved.Atpresent,methodssuchasmaterialdesign,devicestructureandinterfaceoptimizationhavegreatlyimprovedthestabilityofperovskiteLEDs,buttheyhavenotyetreachedtherequirementsofindustrialization.Secondly,thetoxicityofleadinperovskitematerialsmaybeanobstacletoitsindustrialization.Studieshavefoundthatmanyelements(suchastin,copper,germanium,andsilver)canreplaceleadinperovskitematerials,buttheperformanceofdevicespreparedusingtheseelementsisnotasgoodaslead-basedperovskiteLEDs.Inaddition,thelarge-areamodularpreparationofperovskiteLEDsisstillinitsinfancy,andhowtodevelopapreparationprocessforcontrollablelarge-areaproductionstillneedstobesolved.

Inshort,perovskiteluminescentmaterialsanddeviceshaveattractivedevelopmentprospects.Inthefuture,withthein-depthunderstandingofmaterialsandtheprogressofprocesstechnology,itisexpectedthattheefficiencyandstabilityofdeviceswillbefurtherimprovedandtheindustrywillbepromoted.Process.Inthenearfuture,perovskiteLEDswillbecomeastrongcompetitorofanewgenerationofdisplayandlightingwiththeirexcellentperformanceandlowcost,andwilloccupyanimportantpositioninthefuturelightinganddisplayindustry.