PRETREATMENT BY LASER-RADIATION AND ITS EFFECT ON ADHESION IN THE METALLIZATION OF POLY(BUTYLENE TEREPHTHALATE)

Chemical and morphological changes resulting from pretreatment with ex cimer-laser radiation were investigated for poly(butylene terephthalat e) (PBT) surfaces. The irradiated surfaces were coated with aluminum o r copper films of thickness less than or equal to 10 nm, enabling the effects of irradiation on the metal/polymer interface to be studied. I n addition, adhesion was tested for electroplated nickel films on irra diated surfaces. Irradiation was carried out in air with KrF-excimer l aser radiation (lambda = 248 nm) at fluences per pulse in the range ep silon = 3-600 mJ/cm(2). The threshold fluence for material removal, ep silon(t) = 38 +/- 12 mJ/cm(2), was determined by profilometry measurem ents; the morphology of the irradiated surfaces was determined by opti cal and scanning electron microscopy; and the chemical properties of t he polymer and the metal/polymer interface were studied with X-ray pho toelectron spectroscopy (XPS). Depending on the irradiation conditions (fluence, number of laser pulses), various surface morphologies were found, including slightly discolored surfaces, structured surfaces (ri pples), and surfaces with indications of melting and resolidification. The existence regions in irradiation-parameter space for these variou s structures were estimated. Irradiation at fluences near epsilon(t) r esulted in oxygen depletion and bond scission. At higher fluences, the O/C ratio decreased continuously with irradiation, reaching a value s imilar to 30% less than that of the unirradiated surface for irradiati on at epsilon = 401 mJ/cm(2). After deposition of an aluminum overlaye r 3 nm in thickness, the ester (O=C-O) C 1s XPS core level was reduced in intensity, suggesting an aluminum binding site on the carbonyl (O= C) oxygen. Both Al-0 and Al3+ were found, the latter being located at the interface. In comparison with unirradiated areas, irradiated areas exhibited only a slightly higher amount of Al-0 species, indicating n o irradiation-induced enhancement of interfacial metal binding sites. Deposition of a copper overlayer 1 nm in thickness caused a uniform at tenuation of all C 1s core level peaks and only CuO was found for both unirradiated and irradiated surfaces, indicating a weak interaction b etween the metal and the polymer. Electroplated nickel films exhibited enhanced adhesion in irradiated areas for pretreatments that produced structured surfaces (epsilon = 150 mJ/cm(2), N = 50 pulses, roughness R-z similar to 12 mu m), and also for pretreatments for which no stro ng irradiation-induced surface structures were found (epsilon = 3.6-6. 4 mJ/cm(2), N = 1800-3600 pulses).