tg（GlassTransitionTemperature）：玻璃态转换温度，温度一旦高于tg，物理变化非常明显，如同玻璃加热融化。看下面详细的Animportantmaterialpropertyoftendiscussedinsemiconductorpackagingcirclesistheglasstransitiontemperature,orsimplyTg。
BelowaresomekeypointsaboutTg:1)Theglasstransitiontemperature(Tg)ofanon-crystallinematerialisthecriticaltemperatureatwhichthematerialchangesitsbehaviorfrombeing'glassy'tobeing'rubbery'。
'Glassy'inthiscontextmeanshardandbrittle(andthereforerelativelyeasytobreak),while'rubbery'meanselasticandflexible。2)NotethattheconceptofTgonlyappliestonon-crystallinesolids,whicharemostlyeitherglassesorrubbers。
Aglassisdefinedasamaterialthathasnolong-rangeatomicormolecularorderandisbelowthetemperatureatwhicharearrangementofitsatomsormoleculescanoccur。
Ontheotherhand,arubberisanon-crystallinesolidwhoseatomsormoleculescanundergorearrangement。3)Non-crystallinesolidsarealsoknownas'amorphousmaterials'。
Amorphousmaterialsarematerialsthatdonothavetheiratomsormoleculesarrangedonalatticethatrepeatsperiodicallyinspace。4)Atroomtemperature,hammeringapieceofglasswillbreakit,whilehammeringapieceofrubberwon't。
Therubberwouldsimplyabsorbtheenergybymomentarilydeformingorstretching。However,ifthesamepieceofrubberissubmergedinliquidnitrogen(LN2),itwillbehavelikebrittleglass-easytoshatterwithahammer。
ThisisbecauseLN2-cooledrubberisbelowitsTg。5)Forallamorphoussolids,whetherglasses,organicpolymers,orevenmetals,Tgisthecriticaltemperaturethatseparatestheirglassyandrubberybehaviors。
6)IfamaterialisatatemperaturebelowitsTg,large-scalemolecularmotionisnotpossiblebecausethematerialisessentiallyfrozen。IfitisatatemperatureaboveitsTg,molecularmotiononthescaleofitsrepeatunit(suchasasinglemerinapolymer)takesplace,allowingittobe'soft'or'rubbery'。
7)SincethedefinitionofTginvolvesatomicormolecularmotion,timedoeshaveaneffectonitsvalue,i。e。,themechanicalbehaviorofanamorphousmaterialdependsonhowfastaloadisappliedtoit。
Simplyput,thefasteraloadisappliedtoamaterialatitsTg,themoreglass-likeitsbehaviorwouldbebecauseitsatomsormoleculesarenotgivenenoughtimeto'move。
'Thus,evenifanamorphousmaterialisatitsTg,itcanbreakina'glass-like'fashioniftheloadingrateappliedtoitistoohigh。
8)Inthesemiconductorindustry,knowledgeoftheTg'softhevariousmaterialsusedinpackaging(suchasdieattachmaterials,moldingcompounds,andencapsulatingresins)isimportantnotonlyinoptimizingmanufacturingprocesses,butinunderstandingthereliabilityimplicationsofexposureoftheproductstothermo-mechanicalstressesaswell。