Da. Wesner et al., PRETREATMENT BY LASER-RADIATION AND ITS EFFECT ON ADHESION IN THE METALLIZATION OF POLY(BUTYLENE TEREPHTHALATE), Journal of adhesion science and technology, 11(9), 1997, pp. 1229-1242
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).