%\end{itemize}
%\section{The Material Budget}
-The CBM Micro-Vertex-Detector (MVD) has promised to introduce only a very low material budget of $x/X0 \leq 0.3 \%$ in order to deliver a pointing resolution of $4 \mathrm{\mu m}$ in the xy-plane.
-To reach this ambitious goal, all layers of matter in the acceptance of the detector have to be reduced to their current technological minimum while still being affordable and radiation hard.
+The CBM Micro-Vertex-Detector (MVD) depends on employing a material budget $x/X_0$ per detector station of 0.3 \% (first station) to 0.5 \% (following stations) to allow for a secondary vertex resolution of better than $70 \mathrm{\mu m}$.
+To reach this ambitious goal, all components in the acceptance of the detector have to be reduced to their current technological minimum while still being affordable and radiation hard.
+In addtion, the sensor readout has to be robust with low noise occupancy, which puts strong constraints on the electrical properties of the cables connecting the sensor with the close-by FEE.
The reliability of the data acquisition system must be maintained just as well.
-In the process of this optimization, the cable for the sensors of the MVD has caught our attention.
It is built in the form of a flexible printed circuit (FPC) and provides power to the sensors, allows to control them, and to read out the hits.
The previous generation cable was a two-layer cable without vias with a copper layer of only about $18 \mathrm{\mu m}$.
It was successfully tested in a beamtime with the demonstrator\cite{2012 CERN}.
-In the past year we were working on reducing the material budget of those cables further.
Reducing the dominant factor of the material budget meant reducing the thickness of the copper layer as can be seen in the table \ref{tab:material-budget}.
We redesigned the cable with a readout to the side (see figure \ref{fig:cable-layout}), much smaller feature size ($80 \mathrm{\mu m}$) and thus a reduced total cable width, and a very thin copper layer of only $12 \mathrm{\mu m}$.
-The company \textit{ILFA GmbH} has produced a first batch of 20 cables with those specifications recently.
-Their micro-fine production process is a commercial technology they offer -- but still expensive.
+We had a first batch of 20 cables with those specifications produced for us recently.
+Their micro-fine production process is a commercial technology.
% The big contribution of the copper layers to the material budget of the cable can be seen in the table \ref{tab:material-budget}.
Table \ref{tab:material-budget} shows the material budget for the new single-layer cable.
Some problems may arise from the ultra-thin layout though:
-Without an accompanying ground layer, the traces will not have an excellent controlled impedance $Z0$.
+Without an accompanying ground layer, the traces will not have an excellent controlled impedance.
The transmission at 80 MHz is possibly slow enough to tolerate the resulting degraded signal quality.
In addition, the resistance of the power supply lines becomes substantial.
To compensate for this, their width was increased as can be seen in the layout of the cable shown in figure \ref{fig:cable-layout}.
-In future tests it must be evaluated whether the missing shielding and possible impedance mismatch of signal lines as well as the higher resistance of the power supply lines could be a showstopper for this cable.
+Future tests will evaluate the effect of the missing shielding and possible impedance mismatch of signal lines as well as the higher resistance of the power supply lines.
\begin{table}[htb]
\centering
\begin{tabular}{lrrr}
\hline
- Layer & $d [\mathrm{\mu m}]$ & $x/X0$ & Si-equiv $[\mathrm{\mu m}]$ \\ \hline
+ Layer & $d\ [\mathrm{\mu m}]$ & $x/X_0$ & Si-equiv $[\mathrm{\mu m}]$ \\ \hline
Coverlay & 26 & 0.009 \% & 8.6 \\
- Copper & 12 & 0.033 \% & 31.3 \\
+ Copper (40 \%) & 12 & 0.033 \% & 31.3 \\
Polyimide & 25 & 0.009 \% & 8.2 \\ \hline
\textbf{Sum} & 63 & 0.051 \% & 48.1 \\ \hline
\end{tabular}
%
In order to check the function and performance of the new cable, a new sensor test stand was set into place.
One part of this system is a new environment control hardware: a cooling system to stabilize the sensor temperature.
-Other parts of this system include a readout chain for a special test mode of the sensor which allows to measure transfer functions (or `s curves').
+Other parts of this system include a readout chain for a special test mode of the sensor which allows to measure transfer functions.
This system can thus serve to test the sensors for temporal noise and fixed pattern noise.
The next steps will consist of extensive tests of the new cable with this system.
\hline
\ & Copper & Aluminium \\ \hline
$\sigma$ & $5.96 \cdot 10^7 \ \mathrm{S/m}$ & $3.50 \cdot 10^7 \ \mathrm{S/m}$ \\
- $X0$ & $14.36 \ \mathrm{mm}$ & $88.97 \ \mathrm{mm}$ \\
+ $X_0$ & $14.36 \ \mathrm{mm}$ & $88.97 \ \mathrm{mm}$ \\
\hline
\end{tabular}
-\caption{Material properties of Copper and Aluminium. $\sigma$ denotes conductivity and $X0$ denotes the radiation length.}
+\caption{Material properties of Copper and Aluminium. $\sigma$ denotes conductivity and $X_0$ denotes the radiation length.}
\label{tab:material-properties}
\end{table}
% \ & Copper & Aluminium \\
% \midrule
% $\sigma$ & $5.96 \cdot 10^7 \ \mathrm{S/m}$ & $3.50 \cdot 10^7 \ \mathrm{S/m}$ \\
-% $X0$ & $14.36 \ \mathrm{mm}$ & $88.97 \ \mathrm{mm}$ \\
+% $X_0$ & $14.36 \ \mathrm{mm}$ & $88.97 \ \mathrm{mm}$ \\
% \bottomrule
%\end{tabularx}
%\section{Next steps and Outlook}
%
-In the near future, we will test the properties of the new cables.
-Experimenting with leaving out the coverlay? Spray-on instead?
+% In the near future, we will test the properties of the new cables.
+% Experimenting with leaving out the coverlay? Spray-on instead?
\section{Summary}
A new ultra-thin design of the FPC for the CBM Micro-Vertex-Detector was created and the cables produced.
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