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Figure 5. Schematic diagram representing the sequences of the newly proposed electroless plating
(EP) process and showing the differences in the initiation time (
τ
) of the metal deposition when
laboratory-made and commercial Ni and Cu plating baths were used.
the other hand, no metal deposition was observed when the “activated” surfaces
were immersed in the laboratory-made Cu plating bath as well as in the industrial
Ni or Cu plating baths. This means that, even though the reducing agent (formal-
dehyde HCHO) present in all the Cu baths is thermodynamically capable of re-
ducing Pd
+2
ions, it is inoperative for kinetic reasons (infinitely long initiation
time). This is supported by the XPS spectra given in Figure 6. Spectrum (a) repre-
sents the Pd 3d spin-doublet of a PI substrate plasma-treated in NH
3
, and then
immersed in the acidic PdCl
2
solution. The binding energy of the Pd 3d
5/2
peak at
338.0 eV confirms that palladium is surface-grafted as Pd
+2
. Spectra (b) and (c)
are relative to the same sample as (a) after dipping in the laboratory-made Cu
plating bath for 4 min and in the laboratory-made Ni plating bath for 12 s, respec-
tively. In addition, spectrum (d) (Pd 3d
5/2
peak at about 335.5 eV) is a reference
spectrum characteristic of the Pd
0
state. Compared to spectrum (a), the Pd 3d
5/2
peak is slightly more shifted and broadened towards the low binding energy side
for the Pd
+2
-grafted substrate immersed in the Ni plating bath than for that im-
mersed in the Cu plating bath, even though in the latter case the immersion time is
significantly longer. These results clearly indicate that some Pd
0
species are rap-
idly formed during the initiation time of the metal deposition in the Ni plating
bath due to the action of the H
2
PO
2
-
reducing agent, and that the kinetics of the
Pd
2+
reduction is notably slower in the Cu plating bath. Also note that quite simi-
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