ARTICLE IN PRESS

Nuclear Instruments and Methods in Physics Research A 511 (2003) 132–135

Construction of the ATLAS semi-conductor tracker (SCT)barrel modules in Japan
Y. Katoa,*, T. Kohrikib, K. Haraa, Y. Ikegamib, Y. Iwatac, K. Kobayashia,
T. Kondob, M. Kuritad, M. Minagawaa, T. Miyamotod, S. Morinakad, I. Nakanod,
T. Ohsugic, H. Sengokua, S. Shimmaa, R. Takashimae, R. Tanakad, S. Teradab,
N. Ujiieb, Y. Unnob
aInstitute of Physics, University of Tsukuba, Ten0 nodai 1-1-1, Tsukuba-shi 305-8571, Japan
High Energy Accelerator Research Organisation (KEK),Oho 1-1, Tsukuba 305-0801, Japan
cDepartment of Physical Science, Hiroshima 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, JapandDepartment of Physical Science, University of Okayama 3-1-1,Tsushima-naka, Okayama-shi 700-8530, Japane
Kyoto University of Education, Fukakusa-Fujimori 1, Kyoto-shi 612-8522, Japanb

Abstract
We have developed a semi-automated assembly system and constructed 124 silicon microstrip modules so far for theATLAS SCT barrel. This article describes the assembly procedure, evaluations of precisions and the module survey
results. A precision of B2 mm is achievable with this assembly system.
r 2003 Elsevier B.V. All rights reserved.
Keywords: SCT; Precision module assembly; Silicon microstrip detector

1. Introduction
ATLAS semi-conductor tracker (SCT) [1,2] iscomposed of four barrel layers and nine forward
discs at each end, covering the pseudorapidity
range from 2.5 to 2.5. We, ATLAS Silicon Japan
Group, assemble the third layer of the barrel SCT.
The third barrel is made of about 600 modules,
each of which consists of four 64  64 mm2 silicon
microstrip sensors glued back to back on a TPG
baseboard with a stereo-angle of 40 mrad (Fig. 1).

A ﬂexible Kapton-based hybrid, which is backed
with a carbon ﬁber, bridges over the siliconsensors. For high-precision tracking, strip coordinates have to be known with an accuracy of 10 mmin the direction perpendicular to strips (Y direction), and 25 mm in the direction parallel to strips(X direction). Because ﬁnite accuracy of thestereo-angle also deteriorates the resolution, weassemble the modules with the following precisions:
5 mm in deviation of centroids in Y of outer andinner sensor pairs (midyf),* 10 mm in deviation of centroids in X of outerand inner sensor pairs (midxf),* 0.13 mrad in stereo-angle (stereo/2).
**Corresponding author. Tel.: +81-29-853-4270; fax: +8129-853-4491.
E-mail address: you1ka10@hepsg3.px.tsukuba.ac.jp(Y. Kato).

0168-9002/03/$ - see front matter r 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0168-9002(03)01778-9

ARTICLE IN PRESS
Y. Kato et al. / Nuclear Instruments and Methods in Physics Research A 511 (2003) 132–135

Fig. 1. SCT barrel module consists of four silicon microstrip
sensors glued back to back with a stereo-angle of 40 mrad.

The parameter names in parentheses are parts of
24 which we measure in our module metrology
survey [3].
We have developed an assembly system andconstructed 124 modules so far. We describe thedetails of the system and module survey results.

2. Assembly process and jigs
The assembly steps and required times are:(A) align outer sensor pair (B1 h);(B) align inner sensor pair (B1 h);(C) apply adhesive (BN ﬁlled EP-2011) to thebaseboard and align the sensor pairs (>4 h);(D) metrology survey (B1 h);(E) glue the ASIC hybrid (>4 h);(F) wire-bond between sensor pair and between
sensors and ASIC hybrid (B4 h);(G) metrology survey (B1 h).
The glue curing after steps (C) and (E) requires
at least 4 h. We have multiple three sets of jigs
needed for these steps so that we produce twomodules per day.
Fig. 2 illustrates the steps from (A) to (C).
Details of Step (A) are:(A1) Two sensors are put on the pre-alignment
jig, and aligned to a few 10 mm by pushingsensors against alignment pins. The sensors
are vacuum chucked to a transfer plate.

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Fig. 2. Illustration of the sensors alignment steps and jigs. The
details of this system are given in Ref. [4].

(A2) Transfer the sensors on the assembly station.
(A3) Align sensors precisely using CCD cameras
and XYR stages. The CCD cameras canpattern-recognize the sensor ﬁducial marks,the positions being feedback to piezos to ﬁne
adjust the XYR stages.
(A4) Place a transfer plate on the sensors. It isessential to turn off the vacuum of theassembly station prior to turning on thevacuum chuck of the transfer plate.
(A5) Measure the sensor position again, throughholes made in the transfer plate for thispurpose. If the sensors slip at (A4), repeat
from (A3) again.
Step (B) is identical to the above.
The alignment between the two sensor pairs
relies on the two master pins of the assemblystation, the master pins having an angle of 20 mradwith respect to the strip direction. The two sensor
pairs and baseboard are glued in Step (C) using
another pair of pins which enables movement. The
alignment parameters in Steps (A) and (B) areadjusted after the results of module survey
described in Section 4.

3. Precision of assembly system
Achievable precision depends on CCD camera
resolution, stage stability and master pins accuracy. The CCD pattern-recognition determines theARTICLE IN PRESS134

Y. Kato et al. / Nuclear Instruments and Methods in Physics Research A 511 (2003) 132–135sensor ﬁducial marks within an accuracy of
71 pixel, which is 70.074 mm. The base of theassembly station is moved by servo-motors to lessthan 1 mm linearity over the full module length.
The individual XYR stage is controlled bypiezos. The voltages to the piezos are adjusted
until the measured and set positions agree to lessthan 0.7 mm. The hysteresis characteristic of piezos
can be neglected in this computer-controlled feedback procedure. The jigs have temperature-dependent deformation. We measured this effect to beless than 70.5 mm/ : The assembly room iscontrolled to 2571 . The master pin and hole
are mated via a linear bearing system. The
measured repeatability of the linear bearing system
is about 72 mm.
Finally, the overall assembly precision of about
73 mm should be achievable in midyf, that is after
all the most critical parameter to achieve.

Fig. 3. Histograms of ‘‘optMaxZ’’ and ‘‘stereo/2’’ for 124
modules. Arrows are tolerance limits.

Fig. 4. History and histogram of ‘‘midyf’’ for 124 modules.
Arrows are tolerance limits.

4. Metrology survey method and resultsModules metrology survey is performed with
Mitutoyo Quick Vision Pro250. This machine cansurvey modules three-dimensionally with contrast
edge detection, pattern recognition and focusing.
The machine has a system of one CCD camera andone stage. We improved the stage linearity andcorrected for a shift of optical axis of the CCD
camera when its magniﬁcation changed. Finally,
the survey precision is B1 mm in X and Y ; ando10 mm in Z:
The module precision is expressed in terms of 13
parameters in XY and 11 parameters in Z: We
discuss two (‘‘midfy’’ and ‘‘stereo/2’’) XY parameters and one (‘‘optMaxZ’’) Z obtained from 124modules. The parameter ‘‘optMaxZ’’ is the maximum deviation in Z from a ‘‘standard’’ module
proﬁle. Note that ‘‘midxf’’ is less critical and easierto achieve compared to ‘‘midyf’’.
Fig. 3 shows the histograms of ‘‘optMaxZ’’ and‘‘stereo/2’’. The ‘‘standard’’ shape for ‘‘optMaxZ’’is an average Z-proﬁle determined from the ﬁrst
ﬁve modules. The mean value is shifted by
B0.02 mm because of this limited number ofmodules. Since the distribution is narrow, ‘‘optMaxZ’’ should be well within the speciﬁcation if

we use the ‘‘standard’’ shape re-calculated when
the production is completed.
If ‘‘stereo/2’’ (‘‘midyf’’ or ‘‘midxf’’) is not wellcontrolled, some coordinate calibration would berequired for individual module. The ‘‘stereo/2’’
distribution is well inside the speciﬁcation.
Fig. 4 shows the history and histogram of‘‘midyf’’. In the history, broken lines show when
the assembly parameter which tunes ‘‘midyf’’ isadjusted. We ﬁnd that ‘‘midyf’’ is stable to B2 mm
in each period, and after repeating the survey andparameter adjustment, ‘‘midyf’’ has become accurate to 2 mm, about zero for recent modules.

5. SummaryWe, ATLAS Silicon Japan Group, are assembling SCT modules for the third barrel layer. Our
module assembly system has an excellent accuracy
that fulﬁlls the SCT requirements. From theresults of ﬁrst 124 modules, the assembly system
has proved that it can control ‘‘midyf’’, mostcritical parameter, to B2 mm.
We will produce 700 modules by autumn 2003.

ARTICLE IN PRESSY. Kato et al. / Nuclear Instruments and Methods in Physics Research A 511 (2003) 132–135

References[1] ATLAS Inner Detector Technical Design Report, CERN/
LHCC/97-16 and CERN/LHCC/97-17, 1997.
[2] Y. Unno, Nucl. Instr. and Meth. A 453 (2000) 109.

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[3] ATLAS SCT Barrel Module FDR, SCT-BM-FDR,
2001.
[4] T. Kohriki, et al., Module assembly jigs and assembly stepsof the barrel modules, http://jsdhp1.kek.jp/Bunno/si mod/Jigs/Massembly01May.pdf.