Biostability issues of flash gold surfaces

Being chemically inert and non-toxic and having excellent electrical properties gold is known as one of the most suitable materials for fabrication of long-term implantable electronic devices. In spite of this fact, stability of structures with flash gold finish layers (electroless Ni @ immersion Au or electroless Ni @ electroless Pd @ immersion Au), widely used in electronics packaging, is questionable. Such layer configurations are often characterized as not sufficiently stable by applications in humid or corrosive environments and are poorly investigated under the influence of physiological factors as living tissues, microorganisms and body fluids. In this work biostability of FR4 @ 50 mum Cu @ 4 mum Ni @ 0.1 mum Au in simulated blood plasma was studied. The samples were stressed dynamically in a special circulation system, keeping the values of temperature, pressure and flow velocity similar to the natural parameters of a human body. The alterations in topography and structure integrity, chemical composition and wetting properties of the samples surfaces have been investigated by optical microscopy, atomic force microscopy (AFM), laser profilometry, contact angle measurements, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Cracks formation and delamination of a gold layer, significant mass losses and precipitation of the foreign substances have been observed.