Chemistry Reference
In-Depth Information
are partly superposed stand for a medium ion dose, and pores which are totally
superposed stand for a high ion dose.
Between the extreme structures given in Fig. 5 an infinite number of different
surface profiles can be obtained reproducibly. In this way, the polymer surface
profile can be matched to the requirements of any functional coating which is
subsequently deposited. These functional coatings may include conductive or in-
sulating layers, wear-resistant layers, simple decorative layers and others. Any
deposited layer is reliably anchored in the optimized surface profile of the poly-
mer which ensures high peel strength.
The ion-track technology presented here is useful to modify the surface mor-
phology of most commercially available polymers. Especially, it is useful for
polyimide foils like Kapton, Upilex, Apical and others.
3. APPLICATION EXAMPLE: ADHESIVELESS COPPER-POLYIMIDE
LAMINATE
As an example, the application of ion-track technology in the manufacture of ad-
hesiveless all-polyimide laminates will be shown here. Such laminates are used as
base materials for flexible printed circuit boards. In Fig. 6, cross sections of a
polyimide foil which has been subjected to an ion irradiation and etching treat-
ment are shown. It is clearly visible that latent ion tracks have been expanded
through etching into two bundles of microholes which are inclined symmetrically
to the surface.
The microholes affect only a thin surface layer of about 6 µm thickness due to
the limited penetration depth of the ions. This modified surface layer represents
the “surface-depth relief” mentioned above.
Applying a special vacuum-coating process developed by FRACTAL AG the
“surface-depth relief” of the polyimide film is covered completely with a thin
copper seed-coat. The seed-coat may be deposited on one or both sides of the
polyimide film. After depositing the seed-coat an electroplating process is per-
formed. This process allows to fill the pores uniformly with copper and to deposit
a uniform copper layer up to the desired thickness.
The two different groups of symmetrically oriented microholes filled with cop-
per ensure a high peel strength of the copper coating resulting in an outstanding
stability of the copper-polyimide laminate to thermal and mechanical stresses.
This is depicted in Fig. 7a showing the cross section of a copper-polyimide lami-
nate which has been forced to separate partially by applying a very high peel force
of about 5 N/cm. This gives an impression of the highly effective mechanical in-
terlocking between the copper layer on the top and the polyimide foil on the bot-
tom. Fig. 7b presents the copper surface profile which is obtained after complete
removal of the polyimide substrate by etching.
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