Diffusion of copper in polymer during the metallization of PET

Thin Cu metal layers were deposited on semicrystalline poly(ethylene terephthalate) PET films by thermal evaporation. RBS measurements revealed that, under our metallization conditions, the Cu layers are buried into the polymer bulk. This has also been confirmed by ToF-SIMS measurements which reveal that some PET remain at the top surface. Since the formation of a diffuse interface has important consequences on the adhesive properties, the Cu diffusion was investigated systematically by means of RBS. After metallization, the samples were annealed under vacuum for times varying between 0 and 120 hours at 80, 90, 100, 120 and 140 degreesC, slightly above the glass transition of the PET (67 degreesC). Since the diffusion profiles exhibit a behavior in accordance with Fick's laws, the diffusion coefficients were evaluated. The results are in agreement with a diffusion model based on the Brownian motion of particles in a viscous fluid.