23P021-O
Surface Selective Metallization of PTFE Substrate through AtmosphericPressure Plasma Liquid Deposition Approach
大気圧プラズマ化学液相堆積法によるフッ素ポリマー表面への高密着性金属配線パターン作製
1Kento Ooka, 1Hiroki Akiyama, 1Yuto Yamamoto , 1Yasuhiro Hara, 2Nobuyuki Zettsu
and 1Kazuya Yamamura1
大岡健人, 1 秋山弘貴, 1 山本悠人, 1 原安寛, 2 是津信行, 1 山村和也
1

2Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan
Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603, Japan1
阪大院工 〒565-0871 吹田市山田丘 2-1
2名大院工 〒464-0075 名古屋市千種区不老町

We have demonstrated surface modification of fluoropolymer for adhesion enhancement of
PTFE/electroless copper layer by a combination of an atmospheric pressure plasma treatment with liquid
phase self-assembly, which we named atmospheric pressure plasma liquid deposition. This process allows
one to make high adhesion interface without altering the surface roughness through a graft
copolymerization of P4VP monolayer as a metal-ion trapping layer on a PTFE substrate. The adhesion
strength of the functionalized PTFE sheet binding to an electroless copper layer reached ca. 1.0N/mm. In
this work, we demonstrate the fabrication of patterned copper layer on PTFE substrate.

1. Introduction
Demand for high-frequency and high-speedtransmission have been increased. Fluoropolymer
have attracted a great deal of interest in suchdevices, because of low dielectric and low dielectricloss factor. Poly(tetrafluoroethylene)(PTFE) has
dielectric constant of 2.1 and dielectric loss factorof 0.0002@2GHz in wide temperature range of-40℃ to 250℃ and wide frequency range of
5Hz to 10GHz. Due to its surface inertness,
however, pristine PTFE surface fails to satisfy theadhesive strength against to various metals thatmany of the industries require. Prior surface
treatment before the metallization for making highadhesive PTFE/metal layer interface has beenrequired. Another important requirement is the
direct metallization without seeding PTFE surface
with SnCl2 and Pd(0) catalytic cluster. It has
known that SnCl2 did not work as a catalyst forelectroless plating and inhibited copper deposition.
Therefore, various researches about Pd/Sn
catalyst-free surface metallization process havedemonstrated. In the previous work, we havedemonstrated
surfacemodificationof
fluoropolymer for adhesion enhancement of
PTFE/electroless copper layer by a combination of
an atmospheric pressure plasma treatment withliquid phase self-assembly, which we named
atmospheric pressure plasma liquid deposition(APPLD) approach. This process allows one tomake high adhesion interface without roughening

the surface through a graft copolymerization ofpoly(4-vinylpyridine)(P4VP) monolayer as ametal-ion trapping layer on a PTFE substrate [1-4].
The adhesion strength of the functionalized PTFE
sheet binding to an electroless copper (Cu) layer
reached ca. 1.0N/mm.
In this work, we focused on micro-contact printing(CP) to transfer patterned poly(dimethylsiloxane)(PDMS) stamps to the surface of a PTFE substrate.
As
comparedwith
othersite-selective
methods,CP has several apparent advantages,
such as the convenience of reduplication, simple
procedure, low cost and high speed patterning on alarge substrate area. We demonstrated thefabrication of micropatterned copper layer on PTFE
substrate by APPLD approach.
2. Experimental section
Catalyst-free electroless Cu deposition onto
modified PTFE sheet process composes offollowing five steps: (1) implantation of peroxy
radicals on the PTFE substrate by atmosphericpressure helium (He) plasma treatment; (2) graft
copolymerization of P4VP from the modified PTFE
surface; (3) deposition of copper acetate (CuAc)
thin film onto the P4VP-gtafted-PTFE surface; (4)simultaneous reduction of Cu2+ ion to Cu(0) andspontaneous formation of copper nanoparticles
using atmospheric pressure He plasma; (5)autocatalytic electroless deposition of copper on thePTFE surface seeded with copper nanoparticles.

CuAc(b)Microcontact
printing

PDMS stamp

P4VP-graftedPTFE

(c)

(d)

(e)

Remove stamp

Plasma treatment

Cu electrolessplating

CuAc
thin film

Coppernanoparticle

Intensity/ counts

(a)

970

960
950
940
930
Binding energy/ eVFig. 2. The change in Cu2p XPS spectra ofP4VP-grafted-PTFE sheet before (solid line) and after
stamping CuAc (broken line)
CuAc stamped area

PlatedFig. 1. Schematic of the process steps used to fabricate
patterned copper films on P4VP-grafted-PTFEThe PDMS stamp was fabricated by mixing PDMS
with curative agent by the ratio of 10:1 to various
patterned master silicon substrate and heating to
60℃ for 2h to harden PDMS. Fig. 1 outlines ourapproach to the selective copper metallization ofPTFE substrate: (a) Inking a PDMS stamp withCuAc forms a film of CuAc on the surface of thestamp. (b) CP brings the film of CuAc in contact
with the surface of P4VP-grafted-PTFE. (c) PDMS
stamp is removed and transfers a patterned film ofCuAc to the PTFE surface. (d) Atmosphericpressure He plasma assists to form copper
nanoparticles spontaneously. (e) Immersion in anelectroless copper plating bath deposits copper
selectively over the CuAc transferred regions of thePTFE substrate.
3. Results and discussion
Fig. 2 shows the change in Cu2p XPS spectra ofP4VP-grafted-PTFE sheet before and after CuAc
transcription. By stamping CuAc thin film on theP4VP-grafted-PTFE surface Cu2p1/2 and Cu2p3/2
peak were observed at 952eV and 932eV,
respectively, and transcription of CuAc thin film toP4VP-grafted-PTFE surface was confirmed. We
conducted the exposure to atmospheric pressure He
plasma and the immersion in an electroless copper
plating bath for the PTFE substrate after
transferring CuAc. Fig. 3 shows a photographimage of patterned copper layer on PTFE substrate.
The formation of the electroless copper film wasFig. 3. A image of patterned copper layer on PTFE
substrate. Scale bar is 10mm

confirmed in the CuAc stamped area. From thisresult, it is suggested that selective metallization ofPTFE substrate is possible by patterning of CuAc.
4. Conclusion
We demonstrated the fabrication of patterned
copper layer on PTFE substrate by APPLD
approach. In our process, the formation of theelectroless copper film was confirmed in the CuAc
stamped area. In the future, we will evaluate theproperty of patterning, such as line width andPTFE/Cu adhesion strength.
Acknowledgments
This work was partially supported by a Grant-in-Aidfor challenging Exploratory Research from the Ministryof Education, Science and Culture of Japan (23656105),
which is gratefully acknowledged.
References[1] N. Zettsu, H. Itoh, and K. Yamamura, Thin Solid
Film. 516 (2008) 6683.
[2] N. Zettsu, H. Itoh, and K. Yamamura, Surf. Coat.
Technol. 202 (2008) 5284.
[3] H. Akiyama, N. Zettsu, K. Yamamura, Thin Solid
Film. 518 (2009) 3551.
[4] H. Akiyama, K. Yamamura, N. Zettsu, Trans. Mater.
Res. Soc. Jpn. 35 (2010) 817