Study on the structure and adhesion of copper thin films on chemically modified polyimide surfaces - Polyimides and Other High Temperature Polymers - page 336

Figure 4. N/C ratios of the modified BPDA-PDA surface resulted from the treatment in hydrazine
solution.
EDA) and to 0.27 (after being hydrolyzed by hydrazine). According to the ex-
perimental results shown in Figures 3 and 4, the stoichiometric N/C ratios were
not obtained, which suggests that only part of the surface imide-rings could be
converted to the corresponding amides. The fact that breaking down of the aro-
matic amide bond (as indicated in Fig. 1) took place simultaneously with opening
of the imide ring is likely responsible for this outcome, which leads to shorter
segments. In Figure 3 the optimum conditions for modification in EDA should be
30 min of soaking time in a 30 vol% solution at 80 o C. Despite the fact that the
99.5 vol% of EDA could give rise to a higher N/C ratio, it is not economical due
to the use of much higher concentration of EDA. In Figure 4 where hydrazine was
used as the base, it also shows that an extension of reaction time beyond 30 min
did not significantly affect the N/C ratio.
As far as the modification of 6FDA-ODA surface is concerned, the results are
shown in Table 3; the nitrogen atomic concentration seemed to reach its highest
limit after being immersed in EDA solution for 30 minutes at 50 o C regardless of
the base concentration. In the case of using hydrazine as the reagent, the surface
nitrogen atomic concentration reached the limit after 10 minutes of treatment at
50 o C. A higher concentration of hydrazine could result in a higher N concentra-
tion within the same period of time. However, the N concentration dropped with
treatment time; this is again due to the removal of the outermost layer consisting
of short polyimide segments, resulting in exposure of the layer underneath.
3.3. AFM analysis
The topological changes on PI surfaces before and after the modifications were
recorded by AFM. The images were obtained using the tapping mode. Both the
image and the mean roughness (R a ) were determined by scanning a surface area