Chemistry Reference
In-Depth Information
the applications developed in the present work, it should be mentioned that nu-
merous researches have previously been carried out dealing with the gas-phase
activation of PI surfaces using plasma or UV/VUV treatments in various atmos-
pheres (for example, see refs [34-39]). In addition, adhesion characteristics of Ni
or Cu films electrolessly deposited on the PI substrates from both laboratory-
made and commercially available plating baths are also investigated in the present
work.
2. EXPERIMENTAL
2.1. Material and treatment procedures
In the present work, surface pretreatments and subsequent electroless metalliza-
tions were carried out on 125 µm thick polyimide (PI) substrates (Kapton
®
500
HN foils) produced by DuPont, USA. Before processing, these foils were ultra-
sonically cleaned in ethanol and blown dry with N
2
.
Plasma treatments were performed in a parallel plate RF reactor operating in
the Reactive Ion Etching mode (RIE 80 reactor from Plasma Technology, Bristol,
England). The samples to be surface-modified were placed on the powered elec-
trode. Unless otherwise stated, experiments were conducted under the following
conditions: working pressure: 100 mTorr, gas-flow: 100 sccm, power density: 0.5
W cm
-2
.
VUV treatments were carried out using an Xe
2
* excimer lamp (Excivac Labo-
ratory System from Heraeus Noblelight, Kleinostheim, Germany) emitting an in-
coherent radiation centered at 172 nm. This lamp is mounted in an experimental
setup already described elsewhere [33]. Briefly, the latter consists of two contigu-
ous chambers which can be evacuated individually under moderate vacuum. The
upper chamber in which the excimer lamp is located is separated from the reactor
by a 5 mm thick CaF
2
window. In these studies and unless otherwise stated, the
experimental conditions were the following: working pressure in the reactor: 3.5
Torr, window-sample distance: 1 cm, photon flux estimated between 30 and 40
mW cm
-2
[31].
The seeding of PI surfaces with palladium species first utilized two different
methods. The one consisted in immersing the plasma or VUV-treated substrates
for 2 min in a solution containing 0.1 g/liter SnCl
2
and 0.1 ml/liter concentrated
HCl, rinsing them in DI water (sensitization step) for 1 min, then immersing them
for 2 min in a solution containing 0.1 g/liter PdCl
2
and 3.5 ml/liter concentrated
HCl and rinsing (activation step). The other consisted in immersing the pretreated
substrates in a simple solution containing 0.1 g/liter PdCl
2
and 3.5 ml/liter
concentrated HCl for 2 min and rinsing them (direct activation step).
In a second set of experiments, the seeding of PI surfaces with palladium spe-
cies was carried out using palladium acetate (Pdac) thin films which were depos-
ited by spin-coating (10
3
rpm) from a Pdac solution (0.015 M) in chloroform
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