Metallization of insulators (plastics) using polypyrrole as precoat

1
Metallization of insulators (plastics) using
polypyrrole as precoat D. Yfantis, N. Vourdas, A.
Yfantis, S. Kakos,A. Katsori, N. Yfantis, D.
Schmeisser
Faculty of Chemical Engineering, Dept. III
Materials Science and Engineering, National
Technical University of Athens, Zografou Campus
157 73, Athens Greece Dept. of Applied
Physics, Technical University of Cottbus, P.O.
101344, 03013, Cottbus Germany
Microscopic examination of copper coated ABS/Ppy
specimens Microscope photos of the copper plated
specimens are shown in fig.5.
(a) (b) Fig.5.
Microscope photos of the copper front (a) x50 (b)
x100 These pictures demonstrate the copper front
during the electroplating. Copper propagates from
right to the left. At the left part of the
pictures we observe the copper nucleation on the
Ppy film surface. Surface resistance of Ppy
coatings according to ASTM D-257 We found that
the surface resistance of our ppy coatings varies
between 6.5 and 60 KO/square. These measurements
are close to values found in literature (Uribe et
al.). Rate of copper electrodepositing The rate
of copper electrodepositing is constant during
the process and it was found to be about
0.0030gr/min. We also attempted to plate the
ABS/Ppy electrode in a nickel bath without
success. The overpotential of nickel deposition
on Ppy is too high as opposed to the
overpotential of copper on Ppy. Adhesion test
of copper electrodeposit The adhesion of copper
deposit was tested according to the ASTM D 3359,
method B (Cross-Cut Tape Test). Two specimens
were tested. In the first specimen tested 42 of
the deposit was peeled off while in the second
one 66 was peeled off. Photos of the tested
specimens are shown in fig.6. Fig.6.
Photographs of the tested specimens The peeling
of copper coating is due to the poor adhesion of
the Ppy film on ABS. Comparison of conventional
methods to our method Our method offers an
attractive alternative compared to the
conventionall methodology as shown in the
following table. Table 1 Flow sheets
of the conventional industrial method for ABS
metallizing and our method.
1. Introduction In recent years, intrinsically
conductive polymers have attracted much attention
not only from a theoretical point of view but
also in applied science and technology. Among
others, polypyrrole (Ppy) is one of the most
widely used conductive polymers, due to its high
chemical and physical stability, low toxicity of
the monomer (i.e. pyrrole Py) and its easy
chemical or electrochemical synthesis, even in
aqueous solutions. In this work Ppy is used for
copper electrodepositing on a non-conductive
polymer (Acrylo Butadiene Styrene-ABS). The
latter is used as substrate of nickel and
chromium coatings for anticorrosive and
decorative purposes The conventional industrial
methods are usually based on an initial step of
electroless metal deposition taking place on a
catalyzed substrate surface (Pd). These methods
demand many steps in order to achieve the desired
quality, and also require hazardous solutions,
like sulfuric-chromate acid and precious metal
catalysts.
2. Experimental Our method is based on producing
chemically in situ precoats of a conductive Ppy
film on the non-conductive substrate (ABS). This
alters the surface from insulating state to a
conductive one and afterwards, copper is
electrodeposited. So, a new electrode ABS/Ppy/Cu
is formed that is ready for nickel
plating. Material Specimens of commercial ABS
with dimensions 57mm x 30mm x 4mm were
constructed. For Ppy coatings reagents pro
analysi were used py monomer, ammonium
persulfate (NH4)2S2O8, para-toluene sulfonic acid
PTS, sulfuric acid H2SO4. For copper deposition
two baths were used Bath A150 g/L CuSO4?5H2O, 50
g/L H2SO4, 50 g/L ?t?? Bath B (commercial acid
copper)240 g/L CuSO4?5H2O ? 61,104 g/L total
copper, 70 g/L H2SO4, 0,12 g/L ?Cl, 5 g/L
brightener For Nickel deposition a commercial
bath was used 150 g/L nickel sulfate
(?iSO47H2O), 150 g/L nickel chloride
(?iCl26H2O), 50 g/L boric acid, 5 g/L nickel
dispersion additive, 0,8 g/L nickel brightener, 1
g/L special additive Deposition of PPy
coatings First, ABS specimens are etched by
immersion for 15 min in firmly agitated aqueous
solution containing 8 (NH4)2S2O8 . Ammonium
persulfate . also acts as an oxidant in the
polymerization stage that follows. PPY is
polymerized on ABS surface, from an appropriate
optimized solution that contains 3.6 pyrrole and
4.4 PTS that acts as a dopant. By that, a new
electrode is formed that can be electroplated.
Copper electroplating Figure1. Setup
for copper plating of the ABS/PPY
electrode Nickel plating The ABS/Ppy/Cu
electrode is electroplated in a cell at constant
temperature using a nickel ion bath and two
nickel anodes.
The ABS/Ppy electrode is electroplated using the
electrolytic cell shown in figure 1 that contains
a copper ion bath. Copper is deposited onto
ABS/Ppy surface and an ABS/Ppy/Cu sample is
formed. The electrodeposition process was
monitored either potentiostaticaly or
galvanostaticaly. The potential and the current
imposed varied in the experiments.
Conventional Industrial Method Degreasing Polymer
etching (chrome-sulfuric acid) Rinsing Immersion
in PdCl2 solution Surface activation /
reduction of Pd2 by SnCl2 Electroless Copper or
Nickel plating Degreasing (10H2SO4) Rinsing Elect
rodeposition of Copper Further processing
Our Method (laboratory scale) Polymer etching
with (NH4)2S2O8 In situ Ppy chemical
deposition Rinsing (water) Drying Electrodepositio
n of Copper Further processing

• 3. Results and discussion
• The different stages of the process are shown in
  fig. 2
• (a) (b)
  (c)
• Fig..2. (a) Ppy coating (b) copper
  electrodeposition (c) nickel electrodeposition
• XPS spectra
• In figure 3 the XPS spectrum of C1s in each stage
  of the process is shown ABS 1 (ref. specimen,
  without any treatment), ABS 2 (after the etching
  stage), ABS 3 (after the Ppy coating), ABS 4
  (after the copper electroplating), ABS 5 (after
  the electroless copper deposition).
• Fig.3. XPS spectra of the ABS specimens after
  each stage of the process

• Conclusions
• The results prove that the ABS/Ppy electrode has
  sufficient conductivity to allow the copper
  plating
• The front of the copper plating propagates in a
  semicircular manner starting from the point of
  the electric contact of the ABS/Ppy electrode
  with the current source.
• The mechanism of copper deposition on Ppy is
  different compared to the mechanism of copper
  ion deposition on a metal electrode.
• Nucleation of copper on Ppy surface is the
  dominant mechanism.
• The XPS spectra showed that during copper
  plating, copper atoms diffuse in the Ppy coating.
• Our method developed on a laboratory scale has
  advantages over the conventional methods of
  insulators metal plating. It is exceptionally
  simple, energy - saving and s environmentally
  friendly.
• Further work is necessary in order to improve the
  adhesion of he copper coating on ABS.

References 1S. Lamprakopoulos, D. Yfantis et
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Appel, A. Yfantis, W. Goepel, D. Schmeisser,
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Yfantis, G. Appel, D. Schmeisser, D. Yfantis,
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Surface and Coatings Technology, 151-152, (2002),
p.400-404 5 M. Saurin, S.P. Armes, Journal of
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J. Schultze et al, Electrochimica Acta, 44,
(1999), p. 1847 - 1864 7 F.A. Uribe, J.Valerio,
S. Gottesfeld, Synthetic Metals, 55-57, (1993),
p. 3760-3765 8A. Katsori, Postgraduate Thesis,
Athens 2004, NTUA 9S. Kakos, Postgraduate
Thesis, Athens 2003, NTUA
During the deposition process we noticed that
copper electrodeposit propagates in a
semicircular manner starting from the point of
electric contact as shown in fig.4.
Presented at the 55th annual meeting of the
international Society of Electrochemistry
Thessaloniki, 19-24 September 2004