USE OF HIGH-TEMPERATURE AND HIGH HUMIDITY TO TEST THE ADHESION OF SPUTTERED COPPER TO A POLYIMIDE SURFACE-MODIFIED BY AN AC NITROGEN GLOW-DISCHARGE

We have used an extreme environmental stress test to study the adhesio n of a thin sputtered copper film (0.5 mu m) to flexible polyimide (PI ) substrates between 25 and 125 mu m thick. The polyimide types includ e Kapton (PMDA-ODA) and Upilex (BPDA-PDA). When there was no surface m odification on the PI, the adhesion of the film to Upilex type S was b etter than the adhesion to Upilex type R or Kapton type HN. When the p olymer surface was treated with a simple AC nitrogen glow discharge (N GD), there was an improvement in the adhesion of the film to each of t hese polyimides. This improvement in adhesion became apparent after th e film/substrate combination was subjected to either boiling water or steam for 30 min or more; the difference became quite clear after 2 h. A simple tape test was used to quickly estimate a relative adhesion s trength. In order to compare the effect of our AC NGD treatment with o ther substrate surface modification methods, we used it to improve the coupling of a thick (>10 mu m) layer of copper (via a thin intermedia te chromium layer) to a rigid PI substrate, formed from spin coating i ts precursor onto a silicon wafer. Peel test results were within a fac tor of 2-3 of the corresponding results obtained with a radio frequenc y (RF) plasma and ion beam treatments.