Mechanically roughened substrates

It is often observed that some form of mechanical abrasion will increase the measured joint strength [18]. However, as noted above, such treatments do not generally result in a surface topography with cavities suitable for establishing mechanical interlocking with an adhesive. This can be readily seen on the micro level from electron micrographs (Fig. 3.1a) and on the macro level from optical micrographs of sections taken normal to the surface (Fig. 3.1b) and from Talysurf profilometry measurements (Fig. 3. Ic). 

One effect of mechanical abrasion in an industrial environment is usually to ensure that the substrates are free from release agents, machine oil, grease. 

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Although the mechanisms of polyimide/metal adhesion remain to be fundamentally elucidated, it is generally accepted that the interfacial diffusion of metallic entities into the polyamic acid plays a key role at the interface [156-158]. Two main theories have been reported explaining the adhesion of the Pl/metal bond chemical and mechanical bonding [159]. Initial work emphasized mechanical bonding and most efforts were dedicated to the physical roughening of the substrate by different abrasive methods as well as chemical treatments in order to improve metal to polyimide adhesion by increasing the metal surface area [156,160-164]. 

Normal Raman laser excitation in the visible and NIR region (52) can be used to obtain the SERS effect. The substrate surface is extremely important in providing the necessary enhancement to make the technique as valuable as it has become. A number of substrates have been used (53). These include evaporated silver films deposited on a cold surface at elevated temperature ( 390 K) on a glass substrate, photochemically roughened surfaces (e.g., silver single crystals subjected to iodine vapor, which roughens the surface), grating surfaces, and mechanically abraded and ion-bombarded silver surfaces. 

Kapton polyimide has been widely used in the electronic industry because of its low dielectric constant, good mechanical properties and high thermal stability. Many applications require good adhesion between Kapton polyimide film and metal. Various processes to improve adhesion of metal to Kapton polyimide have been reported in the literature. DeAngelo et al., (D describe a process to form metal oxides on the surface of polyimide to improve adhesion. Other efforts to improve adhesion of a metal layer involve roughening of the surface of polyimide substrate by methods such as cathodic sputtering (2), chemical attack (2., 1), and reactive ion etching (1,4). 

For the past two decades, SERS has been widely studied due to its high sensitivity and specificity [1-5]. It is a powerful tool for determining vibrational spectra of probe molecules on roughened metal substrates [6, 7]. In general, there are two simultaneously operative mechanisms to describe the predominantly SERS effect ... 

Surface Roughening - In adhesive bonding, a commonly used surface preparation technique in which the substrate surface is mechanically abraded. The roughened surface increases bondability by dramatically increasing the number of sites available for mechanical interlocking. 

Implant materials for coating. Prosthetic materials coated with HAp include titanium, Ti-6A1-4V, stainless steel, Co-Cr-Mo, and alumina (Jiang and Shi 1998). These materials are roughened by grit blasting for a mechanical interlock between the melted component of the particle and the substrate. The Ti-6A1-4V and Cr-Co-Mo alloys are the most common. Ideally, the elastic modulus and co-efficient of thermal expansion of the substrate and the coating material will be matched to minimize any residual stresses at the interface. Hydroxylapatite (E = 100 GPa and a = 12 x 10 °C (Perdok et al. 1987)) is... 

Mechanical interlocking occurs when the adhesive penetrates pores and openings in the substrate, producing a "lock and key" effect. This requires the adhesive to "wet" the substrate. Its effect can be enhanced by roughening the surface, thus creating pores and increasing the surface area. 

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