Alternative glues for the production of ATLAS silicon strip modules for the Phase-II upgrade of the ATLAS Inner Detector
Luise Poley, Ingo Bloch, Sam Edwards, Conrad Friedrich, Ingrid-Maria Gregor, Tim Jones, Heiko Lacker, Simon Pyatt, Laura Rehnisch, Dennis Sperlich, John Wilson
aa r X i v : . [ phy s i c s . i n s - d e t ] A p r Alternative glues for the production of ATLAS siliconstrip modules for the Phase-II upgrade of the ATLASInner Detector
Luise Poley a,b , Ingo Bloch a , Sam Edwards c , Conrad Friedrich a , Ingrid-MariaGregor a , Tim Jones d , Heiko Lacker b , Simon Pyatt c , Laura Rehnisch b , DennisSperlich b , John Wilson c a Deutsches Elektronen Synchrotron, 22607 Hamburg and 15738 Zeuthen b Humboldt Universit¨at zu Berlin, 12489 Berlin c University of Birmingham, B15 2TT Birmingham d University of Liverpool, L69 7ZE Liverpool
Abstract
The Phase-II upgrade of the ATLAS detector for the High Luminosity LargeHadron Collider (HL-LHC) includes the replacement of the current Inner Detec-tor with an all-silicon tracker consisting of pixel and strip detectors. The currentPhase-II detector layout requires the construction of 20,000 strip detector mod-ules consisting of sensor, circuit boards and readout chips, which are connectedmechanically using adhesives. The adhesive used initially between readout chipsand circuit board is a silver epoxy glue as was used in the current ATLAS Semi-Conductor Tracker (SCT). However, this glue has several disadvantages, whichmotivated the search for an alternative.This paper presents a study of six ultra-violet (UV) cure glues and a gluepad for possible use in the assembly of silicon strip detector modules for theATLAS upgrade.Trials were carried out to determine the ease of use, thermal conduction andshear strength. Samples were thermally cycled, radiation hardness and corrosionresistance were also determined. These investigations led to the exclusion ofthree UV cure glues as well as the glue pad.Three UV cure glues were found to be possible better alternatives than silverloaded glue. Results from electrical tests of first prototype modules constructed
Preprint submitted to Elsevier April 27, 2016 sing these glues are presented.
1. Introduction
Plans for the Large Hadron Collider (LHC) include an upgrade to be com-pleted around 2025 reaching a luminosity of L = 6 · cm − s − comparedto a nominal luminosity of L = 1 · cm − s − , reached in 2011. The LHCexperiments (ALICE [1], ATLAS [2], CMS [3] and LHCb [4]) also need to beupgraded for the high luminosity phase in order to be able to cope with anincreased primary and secondary interaction rate. For the ATLAS detector,the construction of a new tracking detector is foreseen, since the current InnerDetector (consisting of a pixel detector, a strip-based SemiConductor Tracker(SCT) and a Transition Radiation Tracker (TRT)) is not suited for the antic-ipated high track density and radiation levels. In the current upgrade plans,the tracker will consist only of a pixel tracker and a strip tracker, arranged in acentral region, where silicon sensors are aligned parallel to the beam axis (bar-rel), and a forward region, where sensors are aligned perpendicular to the beamaxis (end-cap). For the silicon strip tracker, the current design foresees about11,000 modules in the central region and about 8,000 modules in the forwardregion. Each module is composed of a silicon sensor, one or more circuit boards(hybrids) and readout chips (application-specific integrated circuits (ASICs)).Using a silver-loaded epoxy glue, ASICs are glued on to a hybrid, which,later in the module production process, is glued directly on to a silicon sensorusing a non-conductive epoxy glue. Electrical connections between the compo-nents are made via ultrasonic wire bonds. In this paper the focus lies on theglue used to connect ASICs and hybrid. The silver-loaded epoxy glue (TRA-DUCT R (cid:13) ≥
70 % (by mass) silver. The high silver contentleads to several disadvantages compared to a non-loaded epoxy glue: a highactivation by irradiation, a short radiation length X and possible corrosion ofcomponents consisting of less noble materials. In addition, the glue requiresa minimum curing time of six hours, which leads to long construction times2or each module. The silver-loaded epoxy glue was chosen in an early phase ofthe module design, when ASICs had to be electrically grounded via their back-planes. Since the ASICs in the current design layout are connected to groundby wire bond connections to the hybrid, a conductive glue is no longer required.Therefore the possibility of replacing the silver epoxy glue with a non-conductingadhesive was investigated and is reported in the following.
2. Selection of alternative adhesives
To be accepted as a possible replacement a glue should not have any ofthe disadvantages of the silver epoxy glue. Thus it is required to have a shortcuring time, a large radiation length and to show neither a high activation afterirradiation nor corrosive effects on other components.In addition, the replacement glue should exhibit a similar or better perfor-mance than for silver epoxy glue for the construction and operation of modules.The glue is required to be able to attach ASICs to hybrids (i.e. to attach siliconto gold) with sufficient strength to withstand forces up to 3 . · − N duringoperation and up to 4 . · − N during transport, to have a low toxicity classi-fication, to be easily dispensed and to show flexibility after curing. As well as asufficiently strong connection, low thermal impedance and reasonably low rela-tive coefficients of thermal expansion between the components, the operation ofmodules in the ATLAS detector requires a working temperature range (includ-ing shocks) of -45 ◦ C to +80 ◦ C and a high radiation tolerance were consideredmandatory.Candidates were selected by searching for commercially available glues match-ing the specified criteria. First, all selected glues were tested for suitability forthe construction process and prototype hybrids, assembled with the replacementcandidates, were produced. The prototypes were then subjected to irradiationand thermal cycling. Afterwards the performance of the glues (in particular,their thermal conduction and shear strength) was investigated. A long-termstudy of possible corrosive effects on aluminium was conducted in parallel to3 igure 1: Overview of the tests performed with selected glues in chronological order: afterglues (UV cure and glue pad) had matched the preselection criteria and were found suitablefor the construction of hybrids, prototypes were built and then subjected to tests of theperformance required for the future ATLAS Tracker. Possible corrosive effects on aluminiumwere investigated in parallel. the tests performed with prototypes. An overview of the different stages of thisstudy is shown in Figure 1.
Four glue types were considered during the first selection process:1. multi-component adhesives (where mixing two or more adhesive compo-nents starts a chemical reaction that leads to a curing of the glue)2. UV cure adhesives (where the glue is cured by applying UV light)3. heat curing adhesives (where a curing process is started by heating theglue)4. pressure sensitive tape (an adhesive film which binds together two com-ponents after pressure has been applied)Adhesives whose curing is started by mixing two or more components werenot selected because their curing times were either too long for an efficientproduction stream or too short for the glue to be dispensed effectively..UV cure glues, which are cured by applying UV or blue light, are rarely usedin combination with gold and have a low thermal conductivity, which limitedthe number of glues that were available. Six UV cure glues were selected forfurther investigations. 4eat cure glues, where heating activates the curing process, usually requiretemperatures of O (100 ◦ C), which exceed the components’ heat tolerance. More-over, increased temperatures can lead to deformations of the positioning toolswhich would complicate the adjustment of glue thicknesses. These glues weretherefore not further investigated.Adhesive films are usually available in thicknesses of several 100 µ m, whichexceed the intended glue thickness of 80 µ m between ASIC and hybrid. Despitethis, one adhesive film (thickness 300 µ m) was selected as a test of principle. The radiation lengths of different unloaded adhesives were estimated to beabout 40 cm or ≈
40 g · cm − (for a density of 1 g · cm − ).For silver epoxy glue with a silver content of 70-90 % the radiation length X was estimated by: 1 X = X i f i X ,i , (1)(where f i are the mass fractions of different components of a material and X ,i their radiation lengths) to be between X = 1 .
22 cm for 70 % silver and X = 0 .
95 cm for 90 % silver.This corresponds to a radiation length a factor 30-40 smaller than for anunloaded glue. In the current detector layout, a particle will pass throughapproximately one glue layer between ASIC and hybrid, when traversing thefuture silicon strip detector, which corresponds to about 100 µ m, equivalent to1 % of the silver epoxy glue radiation length of about 1 cm. A summary of the glues selected for further tests is shown in Table 1. AllDYMAX R (cid:13) glues are declared free of halogens (i.e. ≤
500 ppm) and heavymetals by the manufacturer. For the POLYTEC R (cid:13) and LOCTITE R (cid:13) glues noinformation about the heavy metal content could be obtained.5ure type Viscosity Density[mPa · s] [g · cm − ]TRA-DUCT R (cid:13) R (cid:13) R (cid:13) R (cid:13) UV 2133 [11] UV not specified 1.783M R (cid:13) Table 1: Overview of silver epoxy glue, used on the current SCT modules to connect ASICswith a hybrid, and possible replacements with selected properties
3. Construction of module components with alternative glues
The initial construction method was developed using the silver loaded glue(TRA-DUCT 2902) between ASIC and hybrid. A first series of tests was con-ducted in order to determine if a glue’s mechanical properties were suitable forhybrid construction.In order to be glued on to a hybrid, groups of ASICs are picked up usinga vacuum tool. A thin metal sheet stencil is placed on to the back sides ofthe ASICs and through precision openings in the stencil, glue is applied. Afterremoving the stencil, each ASIC carries a glue volume of 1.9 mm consisting offive glue dots with heights of 120 µ m.The ASICs are then positioned above a hybrid at a defined distance of be-tween 60 and 80 µ m, which leads to the 120 µ m glue layer thickness being com-pressed by 33 to 50 %, so that the five dot pattern forms an effective connectionbetween the components. The ASICs are held on the vacuum tool at a fixedheight above the hybrid until the glue is cured.After gluing, ASICs and hybrid are connected electrically by aluminium wirebonds (wire bonding step). 6 .1. Glue dispensing The standard stencil was designed for Tra-Duct 2902 R (cid:13) , which has a highviscosity of 20,000 mPa · s. The UV cure glues under investigation have differentviscosities ranging from highly viscous to highly fluid (see Table 1). In aninitial series of tests it was found that only one candidate (POLYTEC R (cid:13) UV2133, with a high viscosity) could be used with the glue stencil. Highly fluidglues (DYMAX R (cid:13) • a microlitre pipette, which allows a predefined amount of glue to be dis-pensed manually • an automatic glue dispenser, where glue is dispensed by applying pressurefor a specified amount of time to drive the plunger of a glue syringeThe method used must be precise enough that the glue thickness is between60 µ m and 80 µ m, that the glue covers a sufficient area of the ASIC but doesnot squeeze out from underneath the chip.An estimation of the required volume precision can be made by requiringthat the glue, at a thickness of between 60 µ m and 80 µ m, covers a sufficientarea under an ASIC (7 . · . ), but does not squeeze out from underneaththe chip.While a microlitre pipette showed a sufficient volume precision for highlyfluid glues, positioning was done manually and only one-dot glue patterns couldbe achieved. Although the microlitre pipette was used for the construction ofprototypes, alternatives for dispensing the glue were investigated. Automaticglue dispensers used at the Universities of Birmingham and Glasgow were foundto be able to produce dot patterns with high precision alignment for glues withdifferent viscosities (see Figure 2) with good testing results.7 igure 2: UV cure glues dispensed with a microlitre pipette on red plastic (left, DYMAX R (cid:13) R (cid:13) R (cid:13) Both dispensing methods were found to produce good prototypes with noglue squeezing out from below the ASICs. Also the glue dispenser and themicrolitre pipette were found to show smaller variations in the amount of UVcure glue per ASIC than the stencil did with the silver epoxy glue.
In order to cure the UV glue between ASICs and hybrid, UV light wasdirected at the 80 µ m glue layer gap using four light guides (each of diameter2 mm) connected to a commercially available mercury arc lamp. It was foundthat in all trials the glue was completely cured after applying UV light for atotal of 200 s.UV LEDs were investigated as a potentially more cost-efficient UV lightsource. UV LEDs [13], with a 1 W rating and operating at 350 mA with anemitted wavelength of 405 nm, were chosen to match the curing wavelength(350-420 nm) of the chosen glues [7, 8, 6]. The UV LEDs were positioned in analuminium frame with one LED next to each ASIC, with the option to connectthem to a cooling unit and to install them on a vacuum jig surrounding a hybrid.8 igure 3: Scheme of UV curing setups for gluing ASICs on to a hybrid using light guidesconnected to a mercury arc lamp (left) and UV LEDs mounted on an aluminium bar (right),not to scale. While the use of a mercury arc lamp requires the light guides to be moved alongthe edge of the hybrid in order to reach all ASICs (dashed lines), UV LEDs could be used ina static setup where one UV LED was positioned next to the centre of each ASIC. In bothsetups, UV light is applied from the only accessible edge of the ASICs i.e. from the outeredges of the hybrid. Figure 3 shows UV curing setups using UV LEDs and light guides connectedto a mercury arc lamp in comparison.For both setups, a sufficient curing of the whole glue area under each ASICwas confirmed by disassembling the glued components after curing and inspect-ing the glue layers visually or by trying to remove uncured glue with acetone.Figure 4 shows an example of an ASIC glued with LOCTITE R (cid:13) It was found that, after curing, the UV glue layers were still moderatelyelastic, so that bending the hybrid slightly did not loosen the ASICs glued to9 igure 4: Backside of an ASIC glued with LOCTITE R (cid:13) it. This flexibility is a useful feature of UV cure glues. However, a glue layer ofhigh elasticity could potentially cause problems during the wire bonding step asrigid surfaces are required to ensure a sufficiently strong wire bond connectionand to allow the wire bonding machine to operate at maximum speed.All UV cure glues and the glue pad under investigation were found to providegood wire bond connections between ASIC and hybrid. Hybrids glued with UVcure glue (LOCTITE R (cid:13) R (cid:13) After testing glue application, curing and wire bonding, all glues were foundto be suitable for the construction of hybrids. Except for the method of glueapplication and curing, using UV cure glues as alternatives to Tra-Duct R (cid:13) − ≈
20 [14]Copper Hybrid 16.5TRA-DUCT R (cid:13) R (cid:13) R (cid:13) R (cid:13) R (cid:13) R (cid:13) R (cid:13) UV 2133 UV cure glue 35.0 [11]3M R (cid:13) Table 2: List of materials used in components for silicon strip detector modules with co-efficients of thermal expansion (CTE). The adhesives show significantly higher CTE thanconstituents of components. DYMAX R (cid:13) UV cure glues with no specified CTE can be as-sumed to have values of CTE comparable to LOCTITE R (cid:13) UV cure glue because of theirsimilar viscosity, density and composition.
4. Thermal and mechanical glue properties before and after irradia-tion and thermal cycling
After hybrids are constructed at room temperature, their operational tem-perature in the detector will be -20 ◦ C, corresponding to a temperature changeof about 40 K, which can induce stress in components with different coefficientsof thermal expansion. Table 2 summarises the coefficients of thermal expansion(CTE) for several UV cure glues under investigation in comparison with modulecomponent constituents. The different CTE could, over the lifetime of a hybrid,lead to different possible failure scenarios: large mechanical stresses could leadto damaged ASICs or hybrids or failing glue joints, which would result in low11hear strengths or a possible overheating of ASICs. In order to evaluate theseeffects on glue joints, different tests were performed: • single ASIC to hybrid glue joints were shear tested after irradiation andthermal cycling (see section 4.5) • full hybrids were populated, partially irradiated and their thermal perfor-mances monitored during operation (see section 4.8)No adverse effects originating from the mechanical stress induced by the dif-ferent CTE values could be determined. Based on these observations the lesspositive CTE range of the UV cured adhesives was not considered a criterionfor exclusion. The possible long-term weakening of glue joints, caused by repeated tem-perature changes, was investigated in a climate chamber. Each hybrid wassubjected to the same thermal cycling tests as the ATLAS upgrade prototypesensors [15],100 cycles of 14 hrs length per cycle were performed with temperature vary-ing between -20 ◦ C and +50 ◦ C over 60 min and in a controlled low relativehumidity ( ≤
15 %).One hybrid, glued with silver epoxy glue, and two hybrids, each glued withUV cure glue and glue pads, were subjected to this thermal cycling. Of theselatter two, one was constructed using glass dummy ASICs to allow for opticalinspection of the glue joints. Each hybrid was populated with 20 ASICs or glassdummy ASICs.After thermal cycling all glue connections were still intact. Visible changeswere observed for one glue (POLYTEC R (cid:13) UV 2133). Here the glue dot surfaceexposed to the air had turned white, indicating a structural change on thesurface. No visible changes were observed for any other glue.Both the hybrid glued with silver epoxy glue and the hybrid glued witheither UV cure glues or glue pad, were subjected to shear tests after (presented12n section 4.5) thermal cycling in order to determine possible impacts of thethermal cycling on the glue joints.
Information concerning the impact of irradiation on the performance of theadhesives under study was not provided by the manufacturers. A total fluenceof up to 10 n eq /cm (1 MeV neutron equivalent), mainly from hadrons, isexpected in the future ATLAS strip tracker after a runtime of ten years [2]. Asthis fluence is ten times that expected for the current ATLAS SCT, radiationhardness is one of the main requirements for all materials used for construction.the irradiation corresponded to twice the expected total ATLAS fluence. Ir-radiaton of polymers, such as glues, can lead to either a better cross-linking ofthe polymers or a worse interconnection by breaking up large molecules intoshorter chains, depending on the irradiation type and energy, material com-position and temperature [16]. Irradiation tests were performed with 23 MeVprotons at the Karlsruhe Kompaktzyklotron (KAZ) at a temperature of -20 ◦ C.Three test structures were constructed for irradiation: two hybrids, pop-ulated with 20 ASICs each, and a polyethylene plate. One hybrid was gluedwith silver epoxy while the other was constructed with UV cure glues and aglue pad. Glue spots were also dispensed on to a polyethylene plate in order tocheck directly for visible changes in the glue.After irradiation with 2 · n eq /cm it was found that no ASICs had becomedetached from their respective hybrids. Visible changes could be observed for allUV cure glues: POLYTEC R (cid:13) UV 2133 had turned from light brown to white,the DYMAX R (cid:13) and LOCTITE R (cid:13) glues, which are transparent with differentshades of yellow, had turned to a darker shade of yellow, with the extent ofthe colour change varying for the different glues. Although the observed colourchanges were difficult to quantify, the thermo-mechanical characteristics of theglue joints (shear strength and thermal conduction) before and after irradiationwere compared (see sections 4.5 and 4.8).13 .4. Activation of test structures after irradiation The level of activation of an irradiated hybrid was determined by measuringthe spectrum of photons emitted by the sample in the keV to MeV range. Hy-brids glued either with silver epoxy glue or with UV cure glues showed similarlevels of activation. Comparing the gamma spectra of irradiated hybrids, theone with silver epoxy glue shows an additional peak. Due to the complex com-position of the hybrid and the dominant contributions of its metal components,mainly copper, the comparably small activation contribution of the silver (3-4 %of the overall hybrid mass) could not be identified.The measurements suggest that the use of unloaded glues does lead to lowerlevels of activation, but not significantly.
In addition to mechanical stress caused by contraction and expansion dueto temperature changes, gravity and acceleration during transport act on gluejoints. For an ASIC with a weight of 0.04 g, gravity exerts up to 4 . · − N asshear force or pull force during transport, depending on a hybrid’s alignmentangle.Shear tests were performed in order to determine the connection strengthof an ASIC on a hybrid glued with a specific adhesive. For the shear test, ahybrid was screwed down on a holding structure and aligned vertically under amovable shear tool (spatula). The tool’s position was adjusted manually withmicroscrews so that the spatula made contact with the upper edge of the ASIC.After positioning, a steering programme was started which lowered the spat-ula at a predefined rate of 0.5 mm/s and measured the force required to move thespatula at this constant rate against an ASIC. A shear test was stopped whenthe force dropped by 80 %, which usually occured when an ASIC was removedfrom a hybrid. The resulting peak force was taken as a quality criterion for aglue joint’s shear strength. For the initial series of tests b-grade componentswere used, i.e. ASICs with small mechanical damages, such as cracks or brokenedges, so that applying a shear force in some cases caused an ASIC to splinter14eak shear force, [N]after irradiation after thermal cyclingHybrid HybridI II I IITRA-DUCT R (cid:13) R (cid:13) R (cid:13) R (cid:13) R (cid:13) R (cid:13) R (cid:13) UV 2133 - - 20 853M R (cid:13) ≤ ≤ ≤ ≤ Table 3: Peak shear forces for ASICs glued with silver epoxy glue (TRA-DUCT R (cid:13) R (cid:13) UV 2133and 3M R (cid:13) or break instead of being removed from a hybrid. In these cases the determinedshear force was taken only as a lower estimate for the actual shear strength ofa glue joint.The resulting peak shear forces or highest force reached before an ASIC broke(numbers in parentheses) are shown in Table 3. One of the glues (POLYTEC R (cid:13) UV2133) had become brittle after irradiation, so that the glued ASICs fell off thehybrid already during handling. The glue joint was found to have failed insidethe glue rather than at the joint between glue and ASIC or hybrid. Thus thisglue was rejected as possible replacement for the silver epoxy glue.In the case of the glue pad, the spatula moved against an ASIC with the pre-set minimum force of 2 N, moving it continuously downwards. As a consequence,the glue pad was rejected as a valid glue alternative, too.All remaining five UV cure glues under investigation had a sufficiently high15hear strength and even exceeded the results for silver epoxy glue connections.
Using a glue which contains a large amount of silver can lead to diffusionbetween a noble and a less noble metal. This can lead to corrosion of the lessnoble material, when the material with a higher standard electrode potential,draws electrons from the less noble material.In order to monitor possible corrosive effects of the glues under investigation,each glue was dispensed on an aluminium foil in a clean room environment.After several weeks, the contact area between one glue (LOCTITE R (cid:13) R (cid:13) For the remaining four UV cure glues, additional considerations were takeninto account (see Table 4): • Glass transition temperature, i.e. the temperature which marks the tran-sition from solid to the glass-like fluid state. In order to avoid glass tran-sition of a glue layer under an operated ASIC, a glue’s glass transitiontemperature should be high (cf. to 52 ◦ C [5] for silver epoxy glue). Glasstransition temperatures were only provided in the data sheets of two glues:74 ◦ C for DYMAX R (cid:13) ◦ C for LOCTITE R (cid:13) • A high toxicity classification could require additional safety measures forhandling and would thus complicate the construction process. While16lue Rejected Additional considerationsDYMAX R (cid:13) R (cid:13) R (cid:13) R (cid:13) R (cid:13) R (cid:13) UV 2133 brittle after irradiation3M R (cid:13) Table 4: Overview of test results of seven glues under investigation: three glues were rejectedas possible replacements. Among the remaining four UV cure glues DYMAX R (cid:13) DYMAX R (cid:13) R (cid:13) R (cid:13) R (cid:13) R (cid:13) R (cid:13) ◦ C and afterwards removed from thesubstrate. All UV cure glues led to easily removable ASICs after heating andprovided a better reworkability than the silver filled epoxy glue.
During operation, the heat dissipated in the ASICs is transferred to thecooling structure via a thermal path which includes the glue joint between ASICand hybrid. 17pecific thermal conductivities were provided by the manufacturers for theglue pad (3.0 Wm · K ) and one of the UV cure glues (0.1 Wm · K for LOCTITE R (cid:13) Wm · K .In order to investigate the thermal conductivity of the remaining UV cureglues of interest, functional components were used to construct electrically work-ing hybrids. Using either silver epoxy glue or one of the most promising UVcure glue candidates (DYMAX R (cid:13) R (cid:13) R (cid:13) · n eq /cm using 23 MeVprotons.Afterwards, each hybrid was operated on an FR4 circuit board, placed ona cooling jig cooled down to 15 ◦ C. Temperatures of ASICs and hybrid wereestimated from emissions registered using a microbolometer based thermal cam-era [18]. Temperatures were monitored on each ASIC, in comparison with thetemperature of the hybrid, the circuit board and the cooling jig, were measuredbefore and during operation of the hybrid (see figure 5).For each ASIC area, an average temperature was calculated and its minimumand maximum temperatures were used to estimate the temperature uncertainty.Afterwards, the temperature profiles of ASICs glued with UV cure glues werecompared to the temperatures observed on a hybrid glued with silver epoxyglue. Figure 6 shows the comparison for a hybrid glued with DYMAX R (cid:13) igure 5: Thermal image, taken with a microbolometer based thermal camera, of a silverepoxy glued hybrid in operation. The hybrid (outline indicated with dashed white line) isconnected to power (solid white line) and data readout (fine dashed white line) on a testingcircuit board (blue area), positioned on a cooling jig. ASIC temperatures were monitored bymarking their outlines on the thermal camera image (dashed black lines, fine dashed lines forirradiated ASICs) and using their average, calculated by the thermal camera analysis software.Irradiated ASICs (bottom) were found to reach higher temperatures during operation thanunirradiated ASICs. The hybrid temperature was monitored in a similar measurement areabetween the ASICs (solid black line). after irradiation. The silver epoxy glue showed a smaller temperature differencebetween hybrid and ASICs than the UV glued hybrids. Although there is asignificant temperature variation from ASIC to ASIC, the overall difference forthe UV glues is acceptable. This is understandable, as the glue thickness is60-80 µ m and is therefore only one in many contributions to the thermal pathfrom the active area of the ASIC to the centre of the hybrid.In summary, all UV cure glues still considered at this point provided a sat-isfactory thermal connection between ASICs and hybrid which was reasonablyclose to the thermal connection provided by silver epoxy glue.
5. Conclusion and Outlook
Seven glues (six UV cure glues and one glue pad) were investigated, as pos-sible alternatives to the silver epoxy glue currently in use, to connect ASICs andhybrids for silicon strip modules in the ATLAS detector. All glues were tested19
SIC on hybrid
M32 S33 S34 S35 S36 E37 M64 S65 S66 S67 S68 E69 C ] ° T e m pe r a t u r e d i ff e r en c e [ -4-202468101214 Temperature profiles during operation
Temperature difference between ASICs and hybrid T, silver epoxy glue hybrid ∆ T, UV cure glue hybrid ∆ Unirradiated ASICs
Irradiated ASICs
Temperature profiles during operation
Figure 6: Comparison of the temperature profiles measured on a hybrid glued with silverepoxy glue and a hybrid glued with UV cure glue (DYMAX R (cid:13) ◦ C. R (cid:13) UV2133 and 3M R (cid:13) R (cid:13) R (cid:13) R (cid:13) R (cid:13) R (cid:13) R (cid:13) R (cid:13) R (cid:13)
6. Acknowledgements
This work was supported by the Helmholtz-Alliance “Physics at the Teras-cale“ project “Enabling Technologies for Silicon Microstrip Tracking Detectors21t the HL-LHC”.The authors would like to thank Dr. Alexander Dierlamm and Felix B¨ogelspacherfor their help with the planning and realisation of the irradiations conductedfor this study at Karlsruhe Kompaktzyklotron (KAZ).Additional thanks goes to the ATLAS strip tracker community, especiallyDr. Tony Affolder, for providing support and advice for the conducted study.
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