Cleaning the Substrate Surface

Compared to the two methods described above, water-jet cleaning is much simpler and more cost effective. The structured substrate is cleaned by a jet of water at up to 150 bar. The high pressure necessitates the use of workpiece holders, and the method is not suitable for every 3D geometry. Nor is it possible to use this method to clean miniaturized components [189]. 

CO2 snow-jet cleaning is eminently suitable for 3D substrates with pitches 250 pm. The wet-chemical method has advantages in terms of cleaning LSS surfaces and in high-volume production runs. The process of water-jet cleaning is the most economical solution for pitches 300 pm, assuming that the geometries are suitable [189]. 

Specific metallization processes are necessary for the selective deposition of metal coatings on structured thermoplastics. Wet-chemical metallization consists of pretreatment and activation of the plastic surface, followed by chemically reductive or electroless metallization. The systems of metal plating are similar to those 

Etching is followed by seeding with palladium. The palladium nuclei are inserted into the exposed cavities and are catalytically active in the follow-up chemically reductive metallization process. The plastics used in two-shot molding are generally core-catalytic and require no additional seeding or activation. Only the surface has to be etched open to permit access to the catalysts embedded in the plastic [30]. 

Plastics are very good electrical insulators, and this hampers galvanic metallization in MID technology. The electrons required for the purpose cannot be provided by an external electrical source. Chemically reductive metallization baths, also known as electroless baths, are used instead. The electrons are provided by a component of the bath, namely the reductant. A bath of this nature consists of an aqueous metal salt solution, a reductant, and various additives such as chelating agents and stabilizers. In technical parlance, chemical baths of this nature are termed thermodynamically unstable and kinetically inhibited. The art of designing the bath is to make sure that metal deposition starts only at catalytically active areas (the tracks lasered by LDS or the places activated by selective palladium activation) and does not take place where no plating is deposited. This is accomplished by special stabilizers in the bath and by injection of finely distributed air [30]. 

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The steps in a basic hthography process are shown schematicaUy in Fig. 1. The first step in the process generally involves cleaning the surface of the substrate on which the hthography is to be performed and may also involve the application of a surface priming agent A wide variety of both wet chemical and dry plasma methods for cleaning the substrate surface may be employed. If surface... 

I.P.P.D and its relatives have become standard procedures for the characterization of the structure of both clean surfaces and those having an adsorbed layer. Somoijai and co-workers have tabulated thousands of LEED structures [75], for example. If an adsorbate is present, the substrate surface structure may be altered, or reconstructed, as illustrated in Fig. VIII-9 for the case of H atoms on a Ni(llO) surface. Beginning with the (experimentally) hypothetical case of (100) Ar surfaces. Burton and Jura [76] estimated theoretically the free energy for a surface transition from a (1 x 1) to a C(2x 1) structure as given by... 

A superlattice can be caused by adsorbates adopting a different periodicity than the substrate surface, or also by a reconstmction of the clean surface. In figure B 1.21.3 several superlattices that are conmionly detected on low-Miller-index surfaces are shown with their Wood notation. 

Poor preparation of the substrate can result in loss of adhesion, pitting, roughness, lower corrosion resistance, smears, and stains. Because electroplating takes place at the exact molecular surface of a work, it is important that the substrate surface be absolutely clean and receptive to the plating. In the effort to get the substrate into this condition, several separate steps may be required, and it is in these cleaning steps that most of the problems associated with plating arise. 

Good surface preparation is essential, as in all deposition processes, and this can be achieved by chemically cleaning the substrate followed by sputter cleaning with argon just prior to the actual deposition. 

The graph only ever goes through the origin at zero pressure. We have discovered that the only way to have a completely clean substrate (one with no adsorbate on it, with 9 = 0) is to subject the surface to an extremely low pressure - in effect, we have subjected the substrate to a strong vacuum. Effectively, the vacuum sucks the adsorbate away from the substrate surface. We give the name desorption to the removal of adsorbate. 

Liquid chromatographic clean up [441,443,450] has been used either in normal phase flow using alumina, silica, or florisil [22,189,403,481,484] or with reverse-phase (RP) columns [409,452,480]. In most cases these techniques are well established and are used in an off-line mode, primarily to remove the bulk of co-extracted materials prior to a more refined clean-up prior to the final determination. These columns may be prepared in the laboratory [22,403 -405] or commercial solid phase extraction (SPE) cartridges can be used [409,452, 463,470,485,486]. In both cases, the normal phase cartridges and column materials are disposable since many of the polar co-extractants bind firmly to the substrate surface and are difficult to remove. This has been overcome to some... 

The imager of JP-A-6089991 (Toshiba Corp., Japan, 29.03.94) comprises HgCdTe detector regions which have been grown on a silicon substrate. A method to clean the silicon surface before the HgCdTe regions are grown thereon is disclosed. 

By their very nature, heterogeneous assemblies are difficult to characterize. Problems include the exact nature of the substrate surface and the structure of the modifying layer. In this chapter, typical examples are given of how surface assemblies can be prepared in a well-defined manner. This discussion includes the descriptions of various substrate treatment methods which lead to clean, reproducible surfaces. Typical methods for the preparation of thin films of self-assembled monolayers and of polymer films are considered. Methods available for the investigation of the three-dimensional structures of polymer films are also discussed. Finally, it will be shown that by a careful control of the synthetic procedures, polymer film structures can be obtained which have a significant amount of order. It will be illustrated that these structural parameters strongly influence the electrochemical and conducting behavior of such interfacial assemblies and that this behavior can be manipulated by control of the measurement conditions. 

Nickel and its common alloys such as Monel (nickel-copper), Inconel (nickel-iron-chromium), and Duranickel (primarily nickel) can be bonded with procedures that are recommended for stainless steels.35 A simple nitric acid process has also been used consisting of solvent cleaning, immersion for 4 to 6 s at room temperature in concentrated nitric acid, rinsing with cold deionized water, and finally drying. Also, a chromium trioxide-hydrochloric acid process consisting of a 60- to 80-s immersion in acid solution has been suggested. If immersion is impossible, this latter solution may be applied with a cheesecloth after solvent cleaning. The solution is applied to approximately 1 ft2 of the substrate surface at a time, and it remains on the part for approximately 1 min. 

Typical surface preparation calls for cleaning with acetone, MEK, or other common solvent. Once clean, the substrate is then mechanically abraded with sand, grit or vapor blast, or steel wool. The surface is again wiped clean with fresh solvent. Typical adhesives that are employed include epoxies, urethanes, and cyanoacrylates. Polysulfides, furanes, and polyester adhesives have also been suggested. 

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