II-4. Hadron Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Bus-extender development for sPHENIX INTT detectorsPHENIX is a major upgrade of the PHENIX experiment at RHIC, and it aims to study the properties of quark-gluon plasma by measuring jet and upsilon productions and their modiﬁcations. An intermediate tracker (INTT) is a silicon strip barrel detector for sPHENIX.1) A bus-extender is a special cableused for signal transfer between the INTT detector andread-out electronics placed at least 120 cm away fromthe INTT. The bus-extender has the following requirements: (1) ﬂexibility, (2) length, (3) high-density signalline (128 lines/5 cm), and (4) high-speed signal transfer(by LVDS).
We developed a bus-extender in the past threeyears.2) We found that the prototype of our 120 cmlong bus-extender exhibits good electrical performancein terms of signal loss and reﬂection. Some issues werefound in the prototype. The ﬁrst issue is the formation of the through hole. The bus-extender comprises afour-layer ﬂexible printed cuicuit, and the through holeis used to connect the signal lines between layers. We
found that the through hole had a nodule structure,
which can cause instability during long-term use. Figure 1 shows the layer structure of the bus-extender (left)
and the cross section view of the through hole (middle);
the nodule structure is formed in the through hole. We
attempted the production procedure by changing thedrilling methods and Cu-plating methods to remove
the nodules; however, they still existed. We changedResistance (Ω)

T. Hachiya,∗1,∗4 Y. Akiba,∗1 D. Cacace,∗2 K. Cheng,∗3 S. Hasegawa,∗5 D. Imagawa,∗9 H. Imai,∗9 T. Kondo,∗6C. Kuo,∗3 H. -S. Li,∗7 R. -S. Lu,∗8 E. Mannel,∗2 C. Miraval,∗2 M. Morita,∗4 I. Nakagawa,∗1 Y. Namimoto,∗4
S. Nishimori,∗4 R. Nouicer,∗2 G. Nukazuka,∗1 R. Pisani,∗2 M. Shibata,∗4 C. Shih,∗3 M. Stojanovic,∗7
W. -C. Tang,∗3 and X. Wei∗7∗2
∗3
∗4
∗5
∗6
∗7
∗8
∗9sample2

sample3

3.0
2.5
2.0
1.5
1.0
2020/10/5

2020/10/15

2020/10/25

2020/11/4

2020/11/14

2020/11/24Fig. 2. Result of the thermal cycling test (1000 cycles in 50days).

the glue used to laminate the multiple layers; this newglue works eﬀectively. Figure 1 (right) shows the crosssection of the hole with the new glue.
We performed a thermal cycling test to test its longterm stability. The test employs the application of high(75◦ C) and low (−15◦ C) temperatures for 30 min each;the temperature are changed at short time intervals(5 min). We repeated this test for 1000 cycles. We prepared three samples and measured the resistance of thethrough holes to evaluate the stability. These samples
had 400, 600, and 1000 through holes that are daizy
chained. During the test, the polymer of the sample
expands and shrinks because of changes in temperature. This results in cracks in the through hole. If
the through holes have cracks, the resistance becomesa large value. Figure 2 shows the result of the thermal
cycling test. The resistances changes repeatedly within
a valid range because of the changes in temperature forthe entire periods. This indicates that the through hole
has suﬃcent stability.
The second issue is that the peel strength of the prototype is about 4 N. This value is very small comparedwith the standard FPC (20 N). We found that the newglue improved the peel strength to 30–40 N. The results
are summized in Ref. 3).
The radiation hardness and yield rate of the busextender are also studied. The current status of thestudies are summarized in the Refs. 4, 5).
We successfully developed the bus-extender, and weplan to start mass production in 2021.

Fig. 1. (left) Layer structure of the bus-extender. (middle)
Cross section of the through hole made by the originalglue; nodules are formed. (right) Cross section of thehole with the new glue.
∗1

sample1

3.5

RIKEN Nishina Center
Physics Department, Brookhaven National Laboratory
Department of Physics, National Central University
Department of Mathematical and Physical Science, Nara
Women’s University
Japan Atomic Energy Agency
Tokyo Metropolitan Industrial Technology Research InstituteDepartment of Physics and Astronomy, Purdue University
Department of Physics, National Taiwan University
Department of Physics, Rikkyo University

References

1) I. Nakagawa et al., in this report.
2) T. Hachiya et al., in this report.
3) M. Morita et al., in this report.
4) H. Imai et al., in this report.
5) D. Imagawa et al., in this report.

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