Cu layers were fabricated on PET films with and without
pretreatment
by a mixed plasma composed of carbon and copper using a magnetron
sputtering technique for potential application as the flexible copper-clad
laminate (FCCL) in 5G technology. In order to evaluate the effect
of carbon plasma on the composited layer, the graphite target current
was adjusted from 0.5 to 2.0 A. The microstructures and properties
of Cu layers on PET films with different treatments were measured
by an X-ray powder diffractometer, X-ray photoelectron spectroscope,
Raman spectroscope, scanning electron microscope, transmission electron
microscope, scratching test, indentation test, and four-probe detector.
The results showed that the organic polymer carbon structure on the
surface of PET films was changed to inorganic amorphous carbon due
to the effect of the carbon plasma. At the same time, the active free
radicals formed in the transition process react with metal copper
ions to form organometallic compounds. Under the treatment of a mixed
plasma of carbon and copper, the C/Cu mixed layer was formed on the
PET film at the top of the substrate. Due to the presence of C/Cu
mixed interlayers, the bonding strengths between the final Cu layers
and the PET film substrates were improved, and the strongest bonding
strength appeared when the graphite target current was 1.0 A. In addition,
the presence of the C/Cu mixed interlayer enhanced the toughness of
the Cu layer on PET film. It was proposed that the good bonding strength
in combination and the enhanced toughness for the Cu layer on a PET
film was due to the formation of a C/Cu mixed interlayer induced by
the pretreatment of a mixed plasma of carbon and copper.