- Email: [email protected]
Experience in the assembly of the large area silicon tracker for the AMS experiment
ARTICLE IN PRESS
Nuclear Instruments and Methods in Physics Research A 513 (2003) 222–225
Experience in the assembly of the large area silicon tracker for the AMS experiment Maria Ionica*,1 INFN Sezione di Perugia, Via A. Pascoli, Perugia, I-06100 and IMT-Bucharest, Romania
Abstract The Alpha Magnetic Spectrometer (AMS), installed on the International Space Station will provide precise measurements of the cosmic ray spectra in the GeV to TeV energy range, and will search for cosmological antimatter and dark matter. A first version of the detector was operated successfully during a precursor flight on the space shuttle Discovery in June 1998 (STS-91). The magnetic spectrometer uses a large area ð7:2 m2 Þ silicon microstrip detector providing 10 mm spatial resolution for the bending coordinate. Here we briefly report on the design of the AMS tracker, its construction status and some innovative assembly techniques we have developed. r 2003 Elsevier B.V. All rights reserved. PACS: 29.40.Gx; 29.40.Wk; 96.40.De Keywords: Silicon sensors; Tracking and position-sensitive detectors; Astroparticle physics
1. Introduction The aims of the AMS experiment are twofold: to search for new physics in the form of antimatter and dark matter of cosmological origin and to measure with high precision the cosmic ray energy spectra [1]. During a precursor flight in 1998 both the experiment and the silicon tracker performed as expected. In addition, important physics results were obtained [2]. Fig. 1 shows a sketch of the final version of the detector to be installed on the International Space
*Address for Correspondence. IMT-Bucharest, Erou Iancu Nicolae Str. 32, Bucharest R-72996, Romania. Tel.: +39-755852756; fax: +39-75-44666. E-mail address: [email protected] (M. Ionica). 1 Permanent address: IMT-Bucharest, Erou Iancu Nicolae Str. 32, R-72996, Bucharest, Romania.
Station (ISS). The AMS tracker consists of eight layers of double-sided silicon microstrip detectors, mounted on light-weight support planes made of carbon fibre and an Al honey comb. Six layers of silicon sensors, mounted on three 1 m diameter support planes are located inside a 0:8 T superconducting magnet. Two additional layers each mounted on a 1:25 m diameter support plane are placed at the entrance and exit of the magnet. The total sensitive area of the silicon is 7:2 m2 : The AMS microstrip silicon sensors, produced by C.S.E.M. (Centre Suisse d’Electonique et de Microtechnique) [3] are based on the design used for the L3 microvertex detectors at CERN [4]. The main component of the tracker is the ladder, which consists of between 7 and 15 silicon sensors, two low-mass upilex (a polyamide like Kapton) routing cables originally developed for L3-SMD [5], and a pair of front-end hybrids to
0168-9002/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2003.08.036
ARTICLE IN PRESS M. Ionica / Nuclear Instruments and Methods in Physics Research A 513 (2003) 222–225
Fig. 1. The Alpha Magnetic Spectrometer for ISS.
223
silicon microstrip vertex detector of the L3 experiment [4]. A reduced version of the tracker (AMS01) was tested successfully during the shuttle flight STS91. We are now assembling the final version of the tracker for the ISS (AMS02). Both the detector size and readout requirements are significantly increased between the two versions (Table 1). A comparison between the silicon detectors of various space and accelerator experiments is presented in Fig. 3 [9]. Given the large area of the AMS silicon detector an industrial approach is required with a careful optimization of the assembly procedures. A microelectronics company has been chosen (G&A-Site Technology, Italy) which is responsible for the assembly for half of the AMS tracker ladders. A description of the industrial approach for the large area silicon detector assembly is given in Ref. [8]. Table 1 Statistics for SMD, AMS01 and AMS02
Fig. 2. Exploded view of a ladder.
read out the signals of the two sides of the detector (Fig. 2). The front-end hybrids are connected to the ladder via the flexible upilex cables. The hybrids are located at the ladder end near the magnet wall perpendicular with respect to the plane to reduce the non-active area within the magnet bore, and limit the material thickness in the acceptance of the detector. More details of the AMS silicon tracker can be found in Refs. [6–8]. The total number of ladders in the tracker is 192.
No. of ch./ladder No. of bonds/ch. No. of Si/ladder No. of ladders Total no. of ch. Total no. of bonds Total no. of Si Surface ðm2 Þ
L3-SMD
AMS01
AMS02
1 536 12 288 2 48 73 728 589 824 96 0.3
1 024 13 874 12.5 62 63 488 860 160 778 2
1 024 13 216 11.9 192 196 608 2 537 472 2 286 7.2
2. Experience with large area silicon detectors The AMS tracker is based on the experience gained designing, building and operating the
Fig. 3. Surface area of different silicon detectors existing and planned [9].
ARTICLE IN PRESS 224
M. Ionica / Nuclear Instruments and Methods in Physics Research A 513 (2003) 222–225
The technical solutions adopted for the processes of alignment, gluing, and bonding are reported in the next section.
3. Assembly problematic and solutions 3.1. Bonding and gluing Bonding is the most complicated and timeconsuming process. To simplify the process the bonding pad dimensions were increased and aligned to optimize the bonding geometry. A Delvotec ultrasonic bonding machine [10] has been chosen because of its Bond Process Controller (BPC) which allows the modification and control of all relevant parameters, with the capability to record all pre-set parameters and measured values for each bond. Speed has not been sacrificed: 60 wire bonds per minute are made on average. For the AMS ladder bonding we use the same flat wedge as in the L3SMD detectors and 25 mm diameter AlSi1% wire. A thicker wire requires higher bonding power which could damage the silicon sensors in case of bond failures, while too thin wires with low breaking load are dangerous in a space experiment where it will undergo significant vibration. Simplified bonding geometries were implemented (Fig. 4). However, on the n-side of the ladders, at the extremities of each bonding group, a few bonds are made on an unsupported region due to a
Fig. 4. Schematic views of the ladder; critical regions are shown on n-side (up) and p-side, respectively (down).
Fig. 5. Ultrasonic wire bonding failure statistics.
groove in the jig, which accommodates the bonds on the opposite side. In these regions, the first and the last 3–4 wires are very often deformed and in most cases these wires must be removed and remade. These failures represent 61% of the total number of bond failures on both sides. Fig. 5 shows the total number of failures and subtotals on the n- and p-sides. In addition to the problem of the unsupported bonds the most significant contribution to bonding failure was defective upilex metallization on the n-side cables. All failed bonds are recorded and remade. Three percent of the ladders have been rejected in AMS01 because of bad bonding. For gluing operations, we have chosen a precise commercial volumetric dispenser that, together with custom tools, automatically ensures the repeatability and uniformity of the glue dispensing. A small fraction (1.5%) of the rejected ladders was due to the gluing operation [8]. 3.2. Alignment & Metrology A reliable alignment in a ladder is achieved by a precise pin alignment method for the silicon sensors, thanks to the very precise cutting line of the sensors (less than 5 mm for the AMS01 overall production). The AMS mechanical alignment is a simple, cost effective alternative to relatively sophisticated, active positioning systems developed in the context of the large LHC detectors. The precision results obtained in AMS01 (less than 5 mm; Fig. 6) with this method are very encouraging. In the context of AMS02 additional attention has been given to the geometry of the fiducial marks used to record the silicon sensors alignment
ARTICLE IN PRESS M. Ionica / Nuclear Instruments and Methods in Physics Research A 513 (2003) 222–225
225
flight. An industrial approach and the technological solutions developed in the first phase have been validated by the successful operation during the test flight. Fifty AMS02 silicon ladders are already built; the remaining ladders are scheduled to be completed by the middle of 2003. The AMS experiment is scheduled to begin operation aboard the ISS in 2005.
Acknowledgements I express my sincere thanks to the AMS Perugia Tracker Group for their hospitality. I would like to thank William J. Burger and Michele Pauluzzi for their contributions to the preparation of this presentation.
Fig. 6. Alignment precision obtained on the AMS01 ladders built in Perugia.
in the ladders (from crosses to circles) in order to fully automize the metrology. In light of this improvement, a new Mitutoyo 3D metrology machine [11] has been incorporated in Perugia assembly line. The operator involvement is reduced and good repeatability of the measurements is achieved.
4. Conclusions The AMS01 Silicon Tracker has been built and it performed well during the 10 days of the STS-91
References [1] [2] [3] [4]
[5] [6] [7] [8] [9] [10] [11]
R. Battiston, Nucl. Phys. B 65 (1998) 19. AMS Collaboration, Phys. Rep. 366 (2002) 331. C.S.E.M.—Neuch#atel, Switzerland. M. Acciari, et al., Nucl. Instr. and Meth. A 351 (1994) 300; M. Acciari, et al., Nucl. Instr. and Meth. A 360 (1995) 103. G. Ambrosi, et al., Nucl. Instr. and Meth. A 361 (1995) 97. J. Alcaraz, et al., Il Nuovo Cimento 112A (11) (1999) 1325. M. Pauluzzi, Nucl. Instr. and Meth. A 383 (1996) 35. M. Pauluzzi, Nucl. Instr. and Meth. A 473 (2001) 67. Harmuth F.-W. Sadrozinski, talk given at IEEE2000, http://scipp.ucsc.edu/~hartmut/ F&K DELVOTEC Bondtechnik GmbH, Ottobrunn, D-85521. Mitutoyo Italiana s.r.l., 20020 Lainate (Milano), Italy.
Nuclear Instruments and Methods in Physics Research A 513 (2003) 222–225
Experience in the assembly of the large area silicon tracker for the AMS experiment Maria Ionica*,1 INFN Sezione di Perugia, Via A. Pascoli, Perugia, I-06100 and IMT-Bucharest, Romania
Abstract The Alpha Magnetic Spectrometer (AMS), installed on the International Space Station will provide precise measurements of the cosmic ray spectra in the GeV to TeV energy range, and will search for cosmological antimatter and dark matter. A first version of the detector was operated successfully during a precursor flight on the space shuttle Discovery in June 1998 (STS-91). The magnetic spectrometer uses a large area ð7:2 m2 Þ silicon microstrip detector providing 10 mm spatial resolution for the bending coordinate. Here we briefly report on the design of the AMS tracker, its construction status and some innovative assembly techniques we have developed. r 2003 Elsevier B.V. All rights reserved. PACS: 29.40.Gx; 29.40.Wk; 96.40.De Keywords: Silicon sensors; Tracking and position-sensitive detectors; Astroparticle physics
1. Introduction The aims of the AMS experiment are twofold: to search for new physics in the form of antimatter and dark matter of cosmological origin and to measure with high precision the cosmic ray energy spectra [1]. During a precursor flight in 1998 both the experiment and the silicon tracker performed as expected. In addition, important physics results were obtained [2]. Fig. 1 shows a sketch of the final version of the detector to be installed on the International Space
*Address for Correspondence. IMT-Bucharest, Erou Iancu Nicolae Str. 32, Bucharest R-72996, Romania. Tel.: +39-755852756; fax: +39-75-44666. E-mail address: [email protected] (M. Ionica). 1 Permanent address: IMT-Bucharest, Erou Iancu Nicolae Str. 32, R-72996, Bucharest, Romania.
Station (ISS). The AMS tracker consists of eight layers of double-sided silicon microstrip detectors, mounted on light-weight support planes made of carbon fibre and an Al honey comb. Six layers of silicon sensors, mounted on three 1 m diameter support planes are located inside a 0:8 T superconducting magnet. Two additional layers each mounted on a 1:25 m diameter support plane are placed at the entrance and exit of the magnet. The total sensitive area of the silicon is 7:2 m2 : The AMS microstrip silicon sensors, produced by C.S.E.M. (Centre Suisse d’Electonique et de Microtechnique) [3] are based on the design used for the L3 microvertex detectors at CERN [4]. The main component of the tracker is the ladder, which consists of between 7 and 15 silicon sensors, two low-mass upilex (a polyamide like Kapton) routing cables originally developed for L3-SMD [5], and a pair of front-end hybrids to
0168-9002/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2003.08.036
ARTICLE IN PRESS M. Ionica / Nuclear Instruments and Methods in Physics Research A 513 (2003) 222–225
Fig. 1. The Alpha Magnetic Spectrometer for ISS.
223
silicon microstrip vertex detector of the L3 experiment [4]. A reduced version of the tracker (AMS01) was tested successfully during the shuttle flight STS91. We are now assembling the final version of the tracker for the ISS (AMS02). Both the detector size and readout requirements are significantly increased between the two versions (Table 1). A comparison between the silicon detectors of various space and accelerator experiments is presented in Fig. 3 [9]. Given the large area of the AMS silicon detector an industrial approach is required with a careful optimization of the assembly procedures. A microelectronics company has been chosen (G&A-Site Technology, Italy) which is responsible for the assembly for half of the AMS tracker ladders. A description of the industrial approach for the large area silicon detector assembly is given in Ref. [8]. Table 1 Statistics for SMD, AMS01 and AMS02
Fig. 2. Exploded view of a ladder.
read out the signals of the two sides of the detector (Fig. 2). The front-end hybrids are connected to the ladder via the flexible upilex cables. The hybrids are located at the ladder end near the magnet wall perpendicular with respect to the plane to reduce the non-active area within the magnet bore, and limit the material thickness in the acceptance of the detector. More details of the AMS silicon tracker can be found in Refs. [6–8]. The total number of ladders in the tracker is 192.
No. of ch./ladder No. of bonds/ch. No. of Si/ladder No. of ladders Total no. of ch. Total no. of bonds Total no. of Si Surface ðm2 Þ
L3-SMD
AMS01
AMS02
1 536 12 288 2 48 73 728 589 824 96 0.3
1 024 13 874 12.5 62 63 488 860 160 778 2
1 024 13 216 11.9 192 196 608 2 537 472 2 286 7.2
2. Experience with large area silicon detectors The AMS tracker is based on the experience gained designing, building and operating the
Fig. 3. Surface area of different silicon detectors existing and planned [9].
ARTICLE IN PRESS 224
M. Ionica / Nuclear Instruments and Methods in Physics Research A 513 (2003) 222–225
The technical solutions adopted for the processes of alignment, gluing, and bonding are reported in the next section.
3. Assembly problematic and solutions 3.1. Bonding and gluing Bonding is the most complicated and timeconsuming process. To simplify the process the bonding pad dimensions were increased and aligned to optimize the bonding geometry. A Delvotec ultrasonic bonding machine [10] has been chosen because of its Bond Process Controller (BPC) which allows the modification and control of all relevant parameters, with the capability to record all pre-set parameters and measured values for each bond. Speed has not been sacrificed: 60 wire bonds per minute are made on average. For the AMS ladder bonding we use the same flat wedge as in the L3SMD detectors and 25 mm diameter AlSi1% wire. A thicker wire requires higher bonding power which could damage the silicon sensors in case of bond failures, while too thin wires with low breaking load are dangerous in a space experiment where it will undergo significant vibration. Simplified bonding geometries were implemented (Fig. 4). However, on the n-side of the ladders, at the extremities of each bonding group, a few bonds are made on an unsupported region due to a
Fig. 4. Schematic views of the ladder; critical regions are shown on n-side (up) and p-side, respectively (down).
Fig. 5. Ultrasonic wire bonding failure statistics.
groove in the jig, which accommodates the bonds on the opposite side. In these regions, the first and the last 3–4 wires are very often deformed and in most cases these wires must be removed and remade. These failures represent 61% of the total number of bond failures on both sides. Fig. 5 shows the total number of failures and subtotals on the n- and p-sides. In addition to the problem of the unsupported bonds the most significant contribution to bonding failure was defective upilex metallization on the n-side cables. All failed bonds are recorded and remade. Three percent of the ladders have been rejected in AMS01 because of bad bonding. For gluing operations, we have chosen a precise commercial volumetric dispenser that, together with custom tools, automatically ensures the repeatability and uniformity of the glue dispensing. A small fraction (1.5%) of the rejected ladders was due to the gluing operation [8]. 3.2. Alignment & Metrology A reliable alignment in a ladder is achieved by a precise pin alignment method for the silicon sensors, thanks to the very precise cutting line of the sensors (less than 5 mm for the AMS01 overall production). The AMS mechanical alignment is a simple, cost effective alternative to relatively sophisticated, active positioning systems developed in the context of the large LHC detectors. The precision results obtained in AMS01 (less than 5 mm; Fig. 6) with this method are very encouraging. In the context of AMS02 additional attention has been given to the geometry of the fiducial marks used to record the silicon sensors alignment
ARTICLE IN PRESS M. Ionica / Nuclear Instruments and Methods in Physics Research A 513 (2003) 222–225
225
flight. An industrial approach and the technological solutions developed in the first phase have been validated by the successful operation during the test flight. Fifty AMS02 silicon ladders are already built; the remaining ladders are scheduled to be completed by the middle of 2003. The AMS experiment is scheduled to begin operation aboard the ISS in 2005.
Acknowledgements I express my sincere thanks to the AMS Perugia Tracker Group for their hospitality. I would like to thank William J. Burger and Michele Pauluzzi for their contributions to the preparation of this presentation.
Fig. 6. Alignment precision obtained on the AMS01 ladders built in Perugia.
in the ladders (from crosses to circles) in order to fully automize the metrology. In light of this improvement, a new Mitutoyo 3D metrology machine [11] has been incorporated in Perugia assembly line. The operator involvement is reduced and good repeatability of the measurements is achieved.
4. Conclusions The AMS01 Silicon Tracker has been built and it performed well during the 10 days of the STS-91
References [1] [2] [3] [4]
[5] [6] [7] [8] [9] [10] [11]
R. Battiston, Nucl. Phys. B 65 (1998) 19. AMS Collaboration, Phys. Rep. 366 (2002) 331. C.S.E.M.—Neuch#atel, Switzerland. M. Acciari, et al., Nucl. Instr. and Meth. A 351 (1994) 300; M. Acciari, et al., Nucl. Instr. and Meth. A 360 (1995) 103. G. Ambrosi, et al., Nucl. Instr. and Meth. A 361 (1995) 97. J. Alcaraz, et al., Il Nuovo Cimento 112A (11) (1999) 1325. M. Pauluzzi, Nucl. Instr. and Meth. A 383 (1996) 35. M. Pauluzzi, Nucl. Instr. and Meth. A 473 (2001) 67. Harmuth F.-W. Sadrozinski, talk given at IEEE2000, http://scipp.ucsc.edu/~hartmut/ F&K DELVOTEC Bondtechnik GmbH, Ottobrunn, D-85521. Mitutoyo Italiana s.r.l., 20020 Lainate (Milano), Italy.