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surface, strongly impregnated into polyimide surface with excellent adhesion. (All
tests on delamination by using an adhesive tape showed that adhesion was good.)
An SEM micrograph of the surface of metallized (Ag) polyimide Kapton
100HN film is shown in Fig. 3. Surface (dark background) is characterized by a
uniform coating consisting of grains with 0.3-0.5 µm in size covered by light
spots (silver particles) of size 0.4-0.7 µm, some of them achieve size of 1.2-4 µm.
XRFD has shown that black background is silver layer (Fig. 4a) and light spots
are silver particles (Fig. 4b). According to XRFD analysis it is seen that the inten-
sity of silver peaks (silver particles, Fig. 4a) is 316 counts while for background
silver layer (Fig. 4b) it corresponds to 900 counts. According to these data we es-
timate the thickness of silver layer as 2.2-2.5 µm. The SEM micrograph of sil-
vered Upilex 25S film (Fig. 5) shows that silver coating is thinner (intensity - 33
counts, Fig. 5a) and uniform (grain size is around 0.3-0.4 µm) and the largest sil-
ver particle size is 0.5 µm. (Such metallized surface structure is a result of mor-
phology of original films, which is characterized by more uniform compact sur-
face of Upilex film as compared to Kapton).
We believe that during immersion of chelated film into NaBH
4
(pH 10) solu-
tion, silver cations due to their high mobility diffuse back to the surface along
these channels and are reduced in the near-surface layer. So silver particles on the
surface of the film are the result of surface morphology of polyimide films. X-ray
diffractogram of silvered Kapton 100HN film (Fig. 6, 1) shows 111 (θ = 19.105°,
d = 2.3535) and 200 reflections (θ = 22.240°, d = 2.0352) face centered cubic sil-
ver. We believe that silver coating formed by chemical reduction at room tem-
perature and dried at 130°C is characterized by a definite crystal structure. Previ-
ously [29] the study of annealing of PMDA-ODA poly(amic acid) doped with
silver acetate has shown unclear 111 peaks and the absence of other peaks which
were due to two reasons: very thin dispersed form of silver and distortion of crys-
tal lattice. As the cure progresses, silver crystallites grow larger with a corre-
sponding sharpening of the diffraction peaks (Fig. 6) and appearing of new peaks.
We can conclude that in situ chemical metallization of polyimide surface results
in the formation of silver phase with crystal structure. Increase of temperature
leads to reverse diffusion of reduced silver to the surface, and growth and perfec-
tion of crystal lattice.
According to this methodology cobalt and nickel coated Kapton 100HN com-
posite specimens were also prepared. The structure of these coatings is character-
ized by larger size of background metal grains (0.8-1.2 µm) and particles 4 µm
(Figs. 7-8). X-ray diffractometry has shown that cobalt and nickel metal phases
are amorphous (independent of curing). This fact gives reasons to believe that be-
cause of significantly lower mobility of Co
2+
and Ni
2+
cations compared to Ag
+
,
they do not move back to the near-surface layer of the film and are reduced in the
bulk of modified layer. By electrochemical deposition cobalt and nickel, the lay-
ers with lustre can be obtained only in the presence of lustre-forming agents [16].
It is suggested that monomer units of modified polyimide matrix play the role of
lustre-forming agent and form metal grains with a size between 800-1200 nm.
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