New developments in the adhesion promotion of electroless Ni or Cu films to polyimide substrates - Polyimides and Other High Temperature Polymers - page 295

[33]. As an example, Figure 4 is relative to PI substrates NH 3 plasma-treated, and
then activated in a simple acidic PdCl 2 solution. As can be seen, the surface con-
centration of Pd varies as a function of the plasma treatment time similarly to that
of the nitrogenated species.
Given the previous results and remarks, the following conclusions can be
drawn:
1 - Pd +2 species have a strong chemical affinity towards nitrogenated function-
alities and no chemical affinity towards oxygenated functionalities as they are
both grafted through plasma or VUV-assisted treatments. Under these conditions,
Pd-based catalysis of PI surfaces (and more generally of polymer surfaces) can be
carried out using a simplified process involving the surface functionalization with
nitrogenated species and the subsequent surface “activation” by immersion in a
simple acidic PdCl 2 solution. In other words, the creation of Pd-based catalytic
sites occurs selectively onto grafted nitrogenated groups via the chemisorption of
Pd +2 ions and the formation of covalent C-N-Pd bonds.
Figure 4. Plasma treatments of Kapton ® HN samples in NH 3 . Influence of the plasma treatment
time on the oxygen (a), nitrogen (b) and palladium (c) surface concentrations (at.%) after the “acti-
vation” step in the PdCl 2 acidic solution. For comparison, curve (d) is relative to the nitrogen sur-
face concentration before this step, i.e. just after the plasma treatment. The other treatment condi-
tions were: working pressure = 100 mTorr, flow-rate = 100 sccm, power density = 0.52 W cm -2 .