Surface modification of polyimide to improve its adhesion to deposited copper layer - Polyimides and Other High Temperature Polymers - page 326

Figure 11. Peel strength of copper-polyimide laminates after dipping into boiling water. Horizontal
solid line = minimum value of the peel strength required for printed circuit boards. Dotted line = tar-
get range, aim to achieve a higher initial value of the peel strength. Arrow = increasing peel
strength.
In Fig. 11, the results of an additional storage experiment at 75°C are shown.
As expected, the peel strength increases with extended storage time. After reach-
ing a value higher than 1.5 N/mm the sample was dipped into boiling water for 5
minutes. During boiling the peel strength dropped rapidly to the initial value. This
process was repeated three times. In all cases the same initial peel strength value
was observed. The dashed line represents the minimum value of the peel strength
desired for printed circuit boards.
These test results give direction to formulate the next Research & Development
goals: Firstly, a manufacturing process which enables a steeper increase of the
peel strength should be developed. Secondly, and perhaps more important, a proc-
ess which gives a higher initial value of the adhesion has to be developed.
5. SUMMARY
The innovative ion-track technology presented in this paper allows the formation
of “surface-depth reliefs” on polymer foils which are optimised for the subsequent
deposition of functional or decorative coatings. An important application is the