NuclearInstrumentsandMethodsinPhysicsResearchA MultiChipModulestechnologies P
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NuclearInstrumentsandMethodsinPhysicsResearchA MultiChipModulestechnologies P

erlachCLinderBecks Fachbereich PhysikBer ischeUni ersit at WuppertalGaussstrasse 20D42097WuppertalGermany Abstract Inthepastfewyearsimpressiveprogressesinelectronicdevicesandtheirpackaginghavebeenachievedighenergy physicists bene64257t from this bein

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NuclearInstrumentsandMethodsinPhysicsResearchA MultiChipModulestechnologies P




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NuclearInstrumentsandMethodsinPhysicsResearchA473(2001)102–106 MultiChipModulestechnologies P.$erlach%,C.Linder,(.)*.Becks Fachbereich Physik,Ber ischeUni ersit at Wuppertal,Gaussstrasse 20,D-42097Wuppertal,Germany Abstract Inthepastfewyears,impressiveprogressesinelectronicdevicesandtheirpackaginghavebeenachieved.*ighenergy physicists benefit from this, being able to minimise the amount of material in their 2ertex)4etectors. Although the environmentof2ertex)4etectorsismuchmorecontrolledandstabilisedthanintheindustry)orend)user)applications,

therequirementsofmaterial)budgetanddevicecomplexityarehigher. 6hispapertriestogiveashortoverviewoftheexistingMultiChipModuletechnologiesusedin2ertex)4etectorsand focuses on the prototyping results of an upcoming Multi Chip Module technology, called Multi Chip Module) 4eposited(MCM)4),asitisplannedtobeusedfortheinnermostpartoftheA6LA7Pixeldetector. 20018lsevier 7cienceB.2.Allrightsreserved. Keywords: A6LA79Bumpbonding9:lipchip9MCM)49MultiChipModule96hinfilm9Pixel92ertex)4etector 1. Introduction 6herearetwodevelopmentsthathelpadesigner of a 2ertex)4etector to implement an increasing

numberoffeaturesinthesystem.Intheindustry, the first is known as ;;7ystem on a Chip’’ (7oC), meaning that all features are implemented in one integrated circuit. 6his is achieved by enhancing the manufacturing process (mixed signal, BiCMO7,embeddedRAM,etc.). 6heotherwayistobuildthedifferentfunction) alities in separate integrated circuits, using the appropriate process for each part (Bipolar, CMO7, PROM, RAM, N2RAM, etc.) and to build the specific device by mounting the parts needed in a single but complex package. 6his package provides the necessary connections be)

tweenthepartsandtheouterworld. :or 2ertex)4etectors, the requirements on the modulesarequitedifferenttothenormalindustry ones.Coolingissues,forexample,arewellknown in industry, but the temperature and power consumption ranges and the need for material reduction leads to completely different solutions. :ortheplannedhighenergyphysicsexperiments, additional requirements like radiation hardness havetobefaced,whicharemoreorlessunknown in other fields. Protection against environmental impactsmaybereducedtoaminimumin2ertex) 4etectors,causingonetotalkabout hybridisation insteadof

packa in Althoughencapsulationisnotneededin2ertex) 4etector environments, the number of hybrids to be built and installed in the planned high energy physics experiments are orders of magnitudes higher than in the existing ones. *ere, the production process and handling issues become %Correspondingauthor. E-mailaddress: peter.gerlach@cern.ch,gerlach@whep. uni)wuppertal.de(P.$erlach). 016@)A002B01BC)seefrontmatter 20018lsevier7cienceB.2.Allrightsreserved. PIID7 016@)A002(01)0112@)7
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crucialfortheproEects.Inaddition,therisingfrequ)

enciesthatwereusedrequireadefinedbehaviourof theconnectinglines,meaningthatthethicknessof dielectricsandthewidthofsignallineshavetobe verywellcontrolled.6hisleadstothechallengeof improving all the connections within the module, the modules intra-connections , to a robust system withahighqualityfrequencybehaviour. 2. Multi Chip Module techniques 6herearetwowidespreadMCMtechniqueswell knownintheindustry,theMCM)Ceramicandthe MCM)Laminated. 4riven by the rising needs of telecommunication devices, a third one called MCM)4eposited is currently reaching a high volumeproductionstate. 2.1.

M(M-(eramic 6he MCM)Ceramic (sometimes called MCM) Cofiered) provides the most robust modules, demonstrated by its usage in car)engine environ) ments. 6hree types of this technology are usedD 6hick :ilm, *igh 6emperature Cofiered Ceramic (*6CC)andLow6emperatureCofieredCeramic (L6CC). As dielectric materials, Al AlN or glass and as conductors, 6g, Cu or Au are used. 6hemaindifficultyistheshrinkageofthematerial during the firing process, resulting in a difficult dimensional control and the impossibility of building ground)planes due to warpage. On the

otherhand,morethanG0)layersubstratesarebuilt usingthistechnique. 2.2. M(M-)aminated *ere, the layers are built separately and laminated together. 6his allows rigid and flexible modules to be built. 8nhanced lamination steps allow through holes, to connect non)adEacent conductor layers. Copper is used as conductor and as dielectric materials (apton and Ipilex dominate the market9 both are available in a plurality of mutants. Common to both is the absorption of moisture in the range of 1–2 wtJ, resultinginarisingdielectricconstant 6his advanced and flexible technique with a large

number of manufacturers will be used in many planned high energy physics proEects, as it maybefoundintheseproceedings. 2.3. M(M-Deposited 6heMCM)4epositedprovidesthehighestcon) nection density by depositing dielectric and con) ductormaterialsonasubstrate.6hisisdoneusing thinfilmprocessingtechniques. AlorCuisusedasconductormaterial.Copper may be deposited in two different methods. A subtractive method is to sputter the desired thickness of the layer. It is structured afterwards bymaskedetching.Anadditivemethodusesathin sputtered seed)layer as plating base. 6he layer thickness is

achieved by electro)plating the struc) turesneeded.Onlytheseed)layerhastobeetched afterwards.6hefinalmetallisationofthetoplayer may be tuned to the mounting technique. As an example,forsolderbump)bondingitmaybeNiDP withanAucover. 6hethreemainlyavailabledielectricmaterialsare shown in 6able 1. 7ome of them are photo) sensitive,thusreducingthenumberofprocesssteps. Asasummary,6able2showsacomparisonof theMultiChipModuletechniques. 3. The ATLAS MCM-D Pixel Detector Module concept 6he A6LA7 Pixel 4etector will consist of two different types of hybrid pixel modules K1L. :ollowing the

current plans, the larger part will 6able1 4ielectricmaterialsusedforMCM)4eposited Material 6radename Manufacturer Curetemp. PI Pyralin 4uPont 3.3 3G0–400 8poxy Probelec Ciba 4.1 120 BCB C yclotene 4ow 2.6G 2G0 (aptonisaregisteredtrademarkof4owChemical. IpilexisaregisteredtrademarkofIB8. P. Gerlachetal./,uclear-nstruments andMethodsinPhysics.esearch/473 020011102–103 103
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consistofanMCM)Lbasedhybrid.4etailsofthis design may be found in Ref. K2L. 6he innermost barrellayerataradiusofGcmwillberemovable, sohandlingissuesbecomemoreimportant.6aking thisinto account, amoduleconcept

basedonthe MCM)4technologywasprototyped. 6he main idea of the A6LA7 MCM)4 Pixel 4etectorModuleconceptistousethesensor(see Ref.K11L)assubstrateforthethinfilmstructures. 6hesestructuresprovideallmoduleintra)connec) tions. As illustrated in :ig.1, this allows the integration of the signal)lines and the power) supply connections within the module, using bump)bonding flip)chip as the only assembly technique. 6he signal)lines are placed above a ground)planeinamicro)stripconfiguration,guar) anteeing a defined impedance. All the module intra)connections are placed on an

additional, insensitive area of the sensor, which is covered after flip)chipping by the data)buffering and collecting part of the electronic circuits (see Refs. K3,4,10L). MaEor requirements for the thin film techniqueareD highestprocesstemperaturebelow300 G0 micro)stripsignallines, lowpower)supplyconnectionresistance, highinter)connectiondensity. 6hefirstitemiscausedbythesensitivityofthe high resistive, oxygen)enriched silicon substrate. (Above 300 Cthe generation of thermal donors starts.) 6he second and third items are needed to

ensuretheproperfunctionalityofthemodule.6he last item is caused by the need for a connection between each sensor cell through the thin films towards the bump)bond connecting the corre) spondingelectroniccell.6heseconnections,called ;;feedthroughs’’inthefollowing,havetobebuilt withaG0 mpitchintheA6LA7pixelgeometry. :eedthroughsgiveanadditionalcapacitiveand resistiveloadtotheelectronicsfront)end.Butthey givethefreedomtosegmentisethesensorequally, determined only by the area and the number of channels provided by theelectronics.Inaddition, the feed throughs may be used to connect the

readoutcellstoasensorsegmentedina;;bricked way, improving the mean resolution in the long directionofthepixels. 6o achieve the items given above, a process using BenMocyclobutene (BCB, see Chapter 2 3) and electro)plated copper was chosen. In colla) boration with the Fraunho4er -nstitut 4 ur Zu erl assi keitundMikrointe ration (INM,Berlin, $ermany) a successful prototype program has :ig.1. 7chematiccross)sectionofthefourlayerbusandsignalsystem.Ontheright)handside,thefeedthroughconnectionsfromthe detectortothereadoutchipareillustrated. 6able2 8xemplary numbers of the different Multi Chips

Module techniques MCM)C MCM)L MCM)4 Max.no.oflayers G0 20 G 4efinedwaveguides 4ifficult Possible 8asy Min.line)width space 7G 200 7G 7G 10 20 Min.via)diam. pitch A0 200 G0 100 20 G0 Max.proc.temp. @G0–1300 3G0 2G0 7–10 3–4 2.6G Moistureabsorption(wtJ) 1–2 0.2 P. Gerlachetal./,uclear-nstruments andMethodsinPhysics.esearch/473 020011102–103 104
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been carried out, showing that high performing modulescanbebuiltfollowingthisconcept. 3.1. Prototypin results 6o determine the influence of the thin film structures on the performance of the module, a comparison has

been done with the results of the measurements of ;;conventional’’ hybrids. *ere, only the results of the testbeam measurements of thechargecollectionandthespacialresolutionare shownfortheMCM)4hybrids.6heresultsofthe conventionalhybridscanbefoundinRef.KGLand detailed information about other measurements donewithMCM)4hybridsinRefs.K6–AL. 3.1.1. (har e collection 6he increased coupling capacity between adEa) centpixelsmayresultinareducedchargeseenby each electronic cell individually. 6he charge seen may be reconstructed using the calibrated pulse heightinformationgivenbythepixelunitcellK4L.

7electing the appropriate single and double hit events of a testbeam measurement, the Landau distribution can be reconstructed as shown in :ig.2. 6he maxima of these distributions are at the expected value and not changed compared to ;;conventional’’hybrids.6hemaximaofthesingle and the added double hit information is at the same value, meaning that there is no additional chargelossfordoublehits.6heratiobetweenthe number of single and double hits is also not changed. 3.1.2. 6pacial resolution 6he position of a hit pixel may be subtracted fromthetrackpositiongivenbythetestbeamset)

up.6hisresidualgivesthespacialresolutionofthe pixelsystem.In:ig.3,theresolutionsintheshort pixeldimensionofG0 mareshown.6hesinglehit resolution,shownontheleft)handside,resultsina plateauof37 representingthemiddleofthe pixel.*ere,singlehitsaremostprobable.6hetails with a width of G m are caused by the increasing charge sharing between the neighbour) ingpixels. 6herefore,thenumber ofsinglehitsin thisregiondecreases.:ordoublehits,ontheright) hand side of :ig.3, the coordinates of the hit pixels may be weighted with the charge informa) tion,resultinginaresolution ofG Boththe single and double hit

resolutions agree with the onesmeasuredwithconventionalhybridsK2,GL. 4. Conclusion 6he technologies developed in connection with electronicpackaging(asMCM)4)maybeadapted totheneedsof2ertex)4etectors.Buttheirspecific requirements are not always covered by industry, i.e. there is still no flexible MCM)L using aluminium as commercially available conductor. 6heupcomingdevelopmentsdrivenbythemobile telecommunicationhavethepotentialtointegrate passive components in the modules intra)connec) tion structures and new dielectric materials, and largeareaprocessingtechniqueswillresultinnew

waysofbuilding2ertex)4etectors. :ig.2. ReconstructedenergydepositionseenbyanMCM)47ingleChipassembly. P. Gerlachetal./,uclear-nstruments andMethodsinPhysics.esearch/473 020011102–103 10G
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Acknowledgements 6he prototyping program of MCM)4 pixel detectormodules has beendone inthecontext of the A6LA7 Pixel ProEect (C8RN), in close collaboration with the Fraunho4er -nstitut 4 ur Zu erl assi keitundMikrointe ration (INM,Berlin, $ermany). References K1L A6LA7 Pixel 4etector, 6echnical 4esign Report, C8RN L*CC A@)13,(G 1AA@). K2L :. Ragusa, Recent 4evelopments in the A6LA7 Pixel

4etector, Proceedings of the 8ighth International Oork) shopon2ertex4etectors,28R68PAA,20–2GJune1AAA, 6exel, Netherlands, Nucl. Instr. and Meth. A 447 (2000) 1@4. K3L (. 8insweiler, et al., On the performance and limitations ofadualthresholddiscriminatorpixelreadoutcircuitfor L*C, Proceedings of the I888 Nuclear 7cience 7ympo) sium,6oronto,Canada,1AA@. K4L 7.I. Meuser, Pixel Readout Chip for the A6LA7 experi) ment, Proceedings of the I888 Nuclear 7cience 7ympo) sium,6oronto,Canada,1AA@. KGL C. 6roncon, 4etailed studies of the A6LA7 Pixel 4etector, Proceedings of the I888 Nuclear 7cience

7ymposium, October 1AAA, 7eattle, Oash., I888 6rans. Nucl.7ci.47(2000)737. K6L (.)*. Becks, et al., A Multi Chip Module, the basic building block for large area pixel detectors, Procee) dingsof the I888 Mutli)Chip Module Conference, 1AA6, p.16. K7L (.)*. Becks, et al., A MCM)4 type module for the A6LA7Pixel4etector,ProceedingsoftheI888Nuclear 7cience7ymposium,6oronto,Canada,1AA@. K@L M. 6 opper, et al., :abrication of a high)density system using BCB Cu technology, Proceedings of the Interna) tionalConferenceon*igh4ensityPackagingandMCMs, 4enver,Colorado,April1AAA. KAL

C.$rah,Pixel4etectorModulesusingMCM)4technol) ogy, Proceedings of the Pixel 2000, $enova, Italy, 2000 Nucl.Instr.andMeth.A46G(2001)211. K10L R.Beccherle,6heModuleControllerChip(MCC)ofthe A6LA7Pixel4etector,ProceedingsoftheI888Nuclear 7cience7ymposium,6oronto,Canada,1AA@. K11L M.7.Alam,etal.,6heA6LA7siliconsensors,Nucl.Instr. andMeth.A4G6(2001)217. :ig.3. Residuals expected measured position of single hits and weighted double hits, with the latter resulting in a resolution of P. Gerlachetal./,uclear-nstruments andMethodsinPhysics.esearch/473 020011102–103 106