II-9. Instrumentation

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Electrical and mechanical properties of the bus-extender
M. Morita,∗1 Y. Akiba,∗2 D. Cacace,∗3 K. Cheng,∗4 T. Hachiya,∗2,∗1 S. Hasegawa,∗5 D. Imagawa,∗9 H. Imai,∗9T. Kondo,∗6 C. Kuo,∗4 H. -S. Li,∗7 R. -S. Lu,∗8 E. Mannel,∗3 C. Miraval,∗3 I. Nakagawa,∗2 Y. Namimoto,∗1S. Nishimori,∗1 R. Nouicer,∗3 G. Nukazuka,∗2 R. Pisani,∗3 M. Shibata,∗1 C. Shih,∗4 M. Stojanovic,∗7W. -C. Tang,∗4 and X. Wei∗7
The sPHENIX experiment at the Relativistic Heavy
Ion Collider (RHIC) is scheduled to start in 2023 inBrookhaven National Laboratory (BNL). The INTermediate Tracker (INTT)1) is a silicon sensor strip detector to be implemented in the central rapidity region.
The massive raw data generated in INTT need to betransmitted to downstream readout electronics througha quite narrow and curving cabling path for 1.2 m. As
there is no commercial cable available, a high-signaldensity cable was developed using ﬂexible printed cabletechnology. The cable is called “bus-extender” and has
62 pairs of 130-µm-width signal lines. The bus extender
mainly transmits digital signals. The development of thebus extender is in the ﬁnal stage.2)
Owing to the long path length of high-density ﬂexible
printed cables, the poor performance of signal transmission of high-frequency data is a major concern. A simulation predicts 30% attenuation for a 200 MHz signal.
An eye diagram is a useful tool to visually inspect theattenuation and distortion of the signal pulse. We measured the eye diagram by overlaying the waveforms ofvarious bit patterns. The transmission eﬃciency can beevaluated qualitatively by the size of the opening of theeye. Figure 1(a) and (b) show the eye diagram of the lowvoltage diﬀerential signaling (LVDS) signals before andafter passing the bus-extender. From the comparison,
the attenuation of the signal is determined as 33%. The
result is consistent with the simulation. It is found thatthe eye opening after the bus-extender is too small to receive the signals at the readout electronics. To solve theproblem, we increase the drawing current of the LVDS

Fig. 1. Eye diagrams (a) before and (b) after the busextender in the readout chain.
∗1
∗2
∗3
∗4
∗5
∗6
∗7
∗8
∗9Department of Mathematical and Physical Science, Nara
Women’s University
RIKEN Nishina Center
Physics Department, Brookhaven National Laboratory
Department of Physics, National Central 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

Fig. 2. (a) Stress concerning the U-shaped curvature of testpieces. (b) Peeling strength as a function of the peeled
length, evaluated in the region covered by a red circle.

signals from 2 mA to 8 mA to eﬀectively obtain a suﬃciently wider eye opening.
The mechanical properties are also important to assess
the long-term stability and radiation hardness. The bus
extender needs to survive at least three years of operation in a high-radiation environment. The bus-extenderis made using a liquid crystal polymer (LCP) as substrate, instead of a polyimide, which is generally usedfor ﬂexible cables. LCP is a new material used for highenergy physics experiments. Therefore, we studied its
mechanical properties by comparing it with polyimide.
In addition, this study provides a baseline to assess theradiation hardness.
We measured two quantities: (1) ﬂexibility and (2)peeling strength between layers of the multilayered cable. Here, the results of the 2-cm-wide specimen used
are shown instead of results per unit. The former ismeasured by bending the cable in the middle by 180◦ asit forms a “U-shape” inside view. The stress from thecable is recorded for several test samples as a function ofcurvature and is plotted in Fig. 2(a). The ﬂexibility isevaluated by the slope of a 4 N increase in the curvature
region from 0.02 to 0.11/mm. This result is further compared to that from cables exposed to radiation, and no
drastic change was found.3) Therefore, we could obtain
the reference value for ﬂexibility. The latter is measured
by recording the stress of peeling oﬀ the cable as a function of the stroke. The result plotted in Fig. 2(b) showsa peeling strength of 34 to 44 N. This value is twice thatof the polyimide.
We plan to start the mass production of bus-extenders
in 2021. The continuity of all signal lines will be tested
using newly developed test equipment.4)
References

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

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