1. Development of gating foils using FPC production techniques
Masaru Yoshikai (Fujikura Ltd.)
Collaboration study by ILC-TPC Japanese Group
2018/5/29 , ALCW Kyusyu University
自己紹介
xxxxx
I'm happy to talk our activities on this conference.
And Today I introduce our development results for ILC experiment.

2. Prodution of gating foils
Contents
Introduction
Gating foil
Positive ion feedback in ILC-TPC
Prodution of gating foils
Production method
Development results
(3) Summary
- Gating foil for ILC-TPC
(4) Our challenge
First, I explain the contents of my talk.
Today, I mainly explain the Gating foils for ILC-TPC,
and I also introduce our FPC development actvity for High energy physics.
About Gating foils.
I explain
What is the gating foil & Why we need to develop gating foils for ILC TPC
And Next
I explain our development results of Gating foils.
And
I explain the results and current situation.
And Finally
I expain a development of FPC for other experiment of HEP.
2/14

3. Introduction : Gating foil for ILC TPC
■ Time Projection Chamber for ILC TPC
International Large Detector (ILD) is used as a particle detector of ILC.
Time projection Chamber (TPC) with a micro pattern gas detector (MPGD) readout has been proposed as a central tracker.
ILD
TPC
On this page I explain "Why we need the gating foil ?"
Gating foils is special electrode foils for ILC TPC.
TPC(Time projection chamber) using micro pattern gas detector readout has been proposed as a central tracker of the ILC detector.
On this dectaor, We need to amplify the electorn to get signal on the readout of TPC.
So Gas Electorn Multiplier (we call it "GEM") is planned to be used as a gas electron amplification device.
GEM has many good points for the TPC, but has a problem of "Ion Feedback problem".
Fig.1-1 Image of ILD
Fig.1-2 Image of particle tracks
Positive ions in TPC reduce point resolution.
→"Ion feedback problem"
"Gating Foil" is a device to solve the ion feedback problem!!
3/14

4. Gating foil ■ Gating foil for ILC TPC Operated in low voltage
＊GEM : Gas Electron Multiplier
★ Image of gating foil
Cathode
without gating foil
with gating foil
Gating foil E E
GEM
Readout PAD
Fig 2. Image of Gating foil in TPC
★ Function of Gating foil
Transmit electrons
Stop the feedback of ions
- Next I explain about the gating device.
- We mount the foil structure gating device on the amplification module like this figure.
- Gating foil have GEM-like structure like this figure.
- We already know we can get high electron transmission when we operate the GEM in low voltage mode.
- So we can close and open gate by reversing electric filed.
Gate OPEN
Gate CLOSE
★ Operation of gating foil
Operated in low voltage
Open and close by reversing voltage
Fig 3. Electric field of gating foil
4/14

5. Requirement for gating foil
Requirement for gating foil of ILC TPC
Gating foil has GEM-like structure, but required specs are different.
Rim width
70μm
Fig 4-1. Picture of GEM
Item
Amplification GEM
Gating foil
Optical aperture ratio
22.7%
≧80%
Hole size
70μm
≦ 300μm
Hole pitch
140μm
≦335μm
Rim width
≦35μm
Insulator thickness
50μm or 100μm
12.5μm
Foil size
170mm x 220mm
I explain requirement for the gating foil.
over 80% electron transmission is required to satisfy the performance of ILC-TPC.
From the simulation results, the electron transmission is closely related to optical aperture of the gate.
This table shows the details of the requirement, gating foil is required narrow rim and thin thickness insulator structure.
Table 1. Requirement spec for gating foil and amplification GEM of ILC TPC
5/14

6. Production techniques of FPC and GEM
■Flexible Printed Circuit (FPC)
- Fujikura is one of major FPC manufacturer in the world.
FPC (Flexible Printed Circuit)
■Why does Fujikura develop Gating foil?
GEM is producted by FPC production techniques.
Difference of production is the mask design on photolithography process.
Next I explain about the production of Gating foil
First I explain why does fujikura try to develop the gating foil.
Fujikura is one of major FPC maker in the world, and production techniques of amplification GEM are the same as FPC production.
This table shows the production techniques using on GEM and FPC production.
Single mask, Double mask use the photolithography and insulator removing, in case of FPC production this techniques are used in circuit formation.
Key process
GEM production
FPC production
Photolithography
Hole design
Circuit design
Table 2. Production method of FPC and GEM
We think we can apply FPC techniques to gaintg foil processing
6/14

7. Difficulty of gating foil processing
(1) Very fine structure
Item
Gating foil
Optical aperture ratio
≧80%
Hole size
≦ 300μm
Hole pitch
≦335μm
Rim width (Hole pitch - Hole size)
≦35μm
Insulator thickness
12.5μm
Foil size
170mm x 220mm
35μm
Fig5-1. Hole image of the gating foil
Table 3. Required specs of gating foil
(2) Size is very large
Endplate of TPC prototype
100mm
Next what is the difficulty of gating foil production.
Gating foil have very fine structure, narrow rim and thin thickness
Processing of the gating foil is so challenging even for FPC manufacturers.
Fig5-2. Size of FPC and Gating foil
Gating foil development is very challenging!!
7/14

8. Process of gating foil ■Process of gating foil
We tested many process to make the gating foil.
■Process image
(1) Laminate the photoresist film on copper
Copper (Thick)
Photoresist film
Polyimide
Copper (Thin)
Important point
(2) Form Honeycomb structure circuit on the thick copper side
circuit width < 35um
今回いろいろトライしたけれど、最終的に製造したやり方を説明します。
Copper (Thick)
Polyimide
Copper (Thin)
Honeycomb structure
8/14

9. Process of gating foil ■Process of Gating foil
(3) Remove the polyimide by UV-YAG Laser
Laser shot on all area
Defocus beam
of UV-YAG laser
Using the circuit as Laser mask
(4) Etch the copper from both side by etching liquid
Etching speed is 2 times faster
Etcher
Gating foil structure
9/14

10. Circuit formation problem
Development Results
■Defect of process
【Material problem】
【Process problem】
【Others】
Burr
Circuit formation problem
Creasing
Contamination
■Completed process
We already solved all problems.
Optical aperture ratio 82.3%
Thick copper side
Thin copper side
10μm
304μm
12.5μm
31μm
2μm
Fig6-1. Apperance of gating foil
Fig6-2. Cross section of rim
10/14

11. Development Results (1) ILC-TPC module size (170 mm x 220 mm)
The gating foil with large size is developped by using FPC techniques.
Gating foil
Fig7-1. Gating foil
Fig7-2. Gating foil on module
Fig7-3. Magnification of gating foil
(2) Electron transmission ratio
Electron transmission ratio over 80% is conformed by ILC-TPC Group.
Gating foil
please ask the test results to ILC-TPC Group.
fig7-4. Gating foil on the Test module
11/14

12. Gating foil development is required to solve the ion feedback problem.
Summary
Gating foil development is required to solve the ion feedback problem.
We tried to develop the gating foil by using FPC techniques.
We faced many problems in the processing. We succeeded to make gating foil of ILC-TPC module size.
12/14

13. Our New challenge
■FPC for g-2/EDM experiment
We make FPC for g-2/EDM experiment with collaboration of Kyushu University and KEK.
【Specs of FPC】
Min Line / Space = 35 um/35 um
Circuit Q'ty : 2048 lines
Longest line :
L/S = 40 um/40 um & 200 mm
(4) 　FPC Size : 100 mm x 270 mm
(5) 　Structure : Combine 2 FPCs
210 mm
conbine 2 FPCs
95 mm
Fig8-1. Detector of g-2/EDM experiment
Fig8-2. Characteristics of FPC for g-2 experiment
13/14

14. Fin. FPC technology ■Fine pitch ■Multi-layer ■Heat diffusing
　■Millimeter-wave
　■Noize sheild
FPC technology
　■Component Assembly
This is comercial.
　■High-Speed transmission
14/14

15. Back up

16. Introduction : Positive Ion feedback in ILC TPC
Positive-ion feedback from the gas-amplification region to the drift region can deteriorate the position resolution of TPC.
Distortion Maximum 90um
(Simulation results)
Cathode
Charged particle
Positive Ion from GEM
GEM
GEM
GEM
amplification area(GEM)
Readout PAD
Position Ion is made from GEM
Fig 2-1. Positive ion feedback in ILC TPC
Fig 2-2. Image of ILC-TPC
Required point resolution : better than 100 μm for long drift (~2m)