Effects of surface treatment on the adhesion of copper to a hybrid polymer material
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M. Kusevic VTT Electronics, Oulu, Finland
J.K. Kivilahti Laboratory of Electronics Production Technology, Helsinki University of Technology, Helsinki, Finland (Received 25 March 2003; accepted 18 August 2003)
The effects of various surface pretreatments on the adhesion of electroless and sputter-deposited copper metallizations to a hybrid polymer material were investigated. Without pretreatment, the adhesion between copper and the polymer was virtually zero. The adhesion of electroless copper to the polymer was poor regardless of the pretreatment used. However, the wet-chemical pretreatment of the polymer surface markedly increased the adhesion of sputtered copper to the polymer. It preferentially removed the inorganic part of the polymer and formed micropores on the surface. The plasma and reactive ion etching pretreatments, in turn, selectively etched away the organic part of the polymer and noticeably increased the hydrophilicity. Although this resulted in even higher increase in the surface free energy than was achieved with the chemical treatment, the granular surfaces became mechanically brittle. With the help of x-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, and contact-angle measurements and with the recently developed pull test, the physicochemical changes of the wet-chemically pretreated polymer surfaces were demonstrated to have significant effects on the adhesion.
I. INTRODUCTION
Although many advanced interconnection and packaging technologies as well as high-density microvia boards are already available, the rapidly increasing performance and functionality requirements of wireless devices, in particular, demand the development and implementation of disruptive materials and manufacturing solutions. One such solution is to integrate silicon chips and passive components with very-high-density copper wiring into build-up substrates. This can be realized either by the fully additive or semiadditive techniques utilizing photodefinable polymers and chemical metal-deposition processes.1–4 On the other hand, to overcome signal integrity problems and other system performance limitations encountered in very-high-frequency applications, an increasing amount of research is being carried out for employing also optical interconnections at the printed circuit board level.5–7 The technologies enabling the a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 18, No. 11, Nov 2003
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integration of optical and electrical functions in the same polymer substrate implies, among other things, the usage of most advanced photoimagable materials such as inorganic–organic hybrid polymer materials being synthesized with the sol-gel technology.8,9 These materials combine many useful characteristics of polymers and inorganic solids together with excellent optical properties, and therefore they appear exceptionally attractive for the integration of optical waveguides into high-density multilayer pr
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