Plasma polymer adhesion promoters for metal-polymer systems - Polyimides and Other High Temperature Polymers - page 357

Plasma polymer adhesion promoters for metal-polymer
systems
J. FRIEDRICH, ∗ G. KÜHN, R. MIX, I. RETZKO, V. GERSTUNG,
ST. WEIDNER, R.-D. SCHULZE and W. UNGER
Bundesanstalt für Materialforschung und -prüfung (BAM) / Federal Institute for Materials Research
and Testing, Unter den Eichen 87, D-12205 Berlin, Germany
Abstract—The retention of chemical structure and functional groups during plasma polymerisation
was investigated. Usually plasma polymer layers, prepared by continuous wave radio-frequency
plasma, are often chemically irregular in their structures and chemical compositions. To minimise
these irregularities, low wattages and the pulsed plasma technique were applied to avoid fragmenta-
tions. The polymerisation of vinyl and acryl-type monomers was strongly enhanced in the dark
phase (plasma-off) of a pulsed r.f. plasma caused by the reactivity of the vinyl or acryl-type double
bonds. Bifunctional monomers with acryl or allyl double bonds and also polar groups such as OH,
NH 2 , and COOH were used to produce plasma polymers with defined (regular) structures and a high
density of a single type of functional groups. The maximum yields were 30 OH, 18 NH 2 , 24 COOH
groups per 100 C atoms. To vary the density of functional groups a chemical copolymerisation with
“chain-extending” comonomers such as butadiene and ethylene was initiated in the pulsed plasma.
The composition of these copolymers was investigated by XPS and IR spectroscopy.
Homopolymers and copolymer layers were deposited on polypropylene (PP) foils and then alu-
minium was thermally evaporated. The peel force increased considerably and showed a dependence
on the density of functional groups. The plasma polymer deposition was also monitored in situ by
the Self-Exciting Electron Resonance Spectroscopy (SEERS) to show correlations between plasma
parameters and properties of the deposited plasma polymer layers measured “ quasi-in situ ” by cou-
pling the plasma chamber with an XPS spectrometer.
Keywords : r.f. pulsed plasma; plasma polymers with functional groups; copolymers; adhesion
promoting interlayers; metal-polymer systems.
1. INTRODUCTION
Acetylene, ethylene, butadiene and polystyrene have been deposited as thin
polymer films by pulsed plasmas of low wattages as described elsewhere [1]. It is
known that acetylene can react by opening the triple bond. A substitution of H at
the triple bond by organic residues was observed [1]. Ethylene does not form a