Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 51 (2018)

Development of long multi-layered flexible cable of silicon sensor
detector for sPHENIX experiment
M. Tsuruta,∗1,∗2 Y. Akiba,∗1 D. Cacace,∗5 E. Desmond,∗5 T. Hachiya,∗1,∗3 Y. Kawashima,∗1,∗2 T. Kondo∗4E. Mannel,∗5 H. Masuda,∗1,∗2 G. Mitsuka,∗1 I. Nakagawa,∗1 R. Nouicer,∗5 R. Pisani,∗5 K. Shiina,∗1,∗2 andY. Yamaguchi∗1
The progress in the new development of the bus
extender 1) for the sPHENIX intermediate tracker(INTT) is reported. The INTT composed of silicon stripsensors. Due to a tight space budget around the collision area, the space to run signal cables for INTT isstrictly limited. Thus, high density signal transfer cables are required to send signals from silicon sensors to
the front-end readout electronics by 1.3 m. The additional requirements to the cable are ﬂexibility and theimpedance matching with circuits to be connected to.
As deﬁned in the Eqs. (1) and (2), one of the key essencesis the signal line width and pitch.
()
S(1)
Zdif = 2 × Z0 exp 1 − 0.374e−2.9 D60
Z0 = √ lnϵr

(4D0.67π(0.8W + d))(2)Here, Zdif and Z0 are diﬀerential and characteristic
impedance, and ϵr is the relative dielectric constant. For
given impedance, the narrower the line width, the thinner the cable can be. Thus we need to design the signal
line width as narrow as possible for the cable to be ﬂexible.
In order to judge the technological limit of a ﬁnest
width and pitch of the signal line of long ﬂexible print cables (FPCs), we measured a 1.3-m long sample FPC, as

Fig. 1. Cross section of diﬀerential signal lines. S and W
are line width and pitch, respectively. D and d are thickness between ground planes and thickness of signal layer,
respectively.

Fig. 2. Sample FPC
∗1
∗2
∗3
∗4
∗5Fig. 3. Observed line width (y-axis) of the sample FPC(black) and its mask(red). The x-axis is the transverse
distance from the edge of the sample FPC.

RIKEN Nishina Center
Department of Physics, Rikkyo University
Division of Natural Sciences, Nara Womens University
Tokyo Metropolitan Industrial Technology Research InstituteBrookhaven National Laboratory

Fig. 4. Observed line widths of the new prototype FPC(blue) superimposed on these of the sample FPC.

shown in Fig. 2, manufactured by the Print-Electronics
Laboratory. The measurement was conducted for 32 signal lines whose width were designed to be 120 µm.
The observed line widths are plotted in Fig. 3 (blacksymbols). As can be guided by the curve showing asine function ﬁtting, the observed line-width oscillates
by 10 µm with a constant (< 1 mm) repetition. Most
likely, the origin is propagated from the mask itself used
at an exposure process. As shown by black symbols, almost exact pattern was observed in the mask. Therefore,
we employed a higher precision mask printer to produce
the next-round prototype FPC. The resulting line-width
data are superimposed in Fig. 4 on top of previous measurements of the sample FPC. As is apparent from theFig. 4, the new mask successfully provided much better
precision (3 µm) of the line width. There found 10 µm
oﬀset in the line width between the FPC and the mask.
This oﬀset can be diminished by design the line width
10 µm narrower for the mask on purpose.
References- 161 -1) T. Hachiya et al., in this report.
2) I. Nakagawa et al., in this report.