Adhesion of copper to UV photo-oxidized Kapton and Upilex-S polyimide surfaces

Polyimides (PIs), like Kapton® and Upilex-S®, are often used as electrical insulation between levels of circuitry in the manufacture of electronic components. Excellent adhesion between the Cu conductor and the dielectric material is essential in the construction of these microsystem devices. Polyimide, Kapton® HN500 (PMDA-ODA), and Upilex-S® (BPDA-PDA) were exposed to 185/254 nm radiation in the presence of oxygen at atmospheric pressure. Surface modification of the PI surface was investigated by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Time of Flight Secondary Ion Mass Spectroscopy (TOFSIMS). Copper was sputter-coated onto the modified PI surface. To monitor adhesion, tape tests were applied to the Cu/PI substrate. SEM micrographs revealed some changes with Upilex-S while did not show any significant differences in surface morphology following photo-oxidation for Kapton HN. With long treatment times, XPS results showed cohesive failure occurring within the modified PI and not at the PI-Cu interface. Coupling the more microscopic view of the surface by TOFSIMS with the results of XPS, that samples a depth of ca. 2- 10 nm, suggest adhesion failure occurs at a thickness ≤10 nm. There was good practical adhesion between Cu and the modified PI surface. Adhesion test results showed that cohesive failure occurred quicker within Upilex-S than Kapton HN samples