Chemical etching stripping

The best method to clean a metal surface is by vapor degreasing with an organic solvent such as trichloroethane. Effective aqueous systems have also been developed. The next step is sandblasting to increase the adhesive contact surface area by roughening the metal surface. Chemical etching strips away weakly bonded oxides and forms an oxide that is strongly bonded to the bulk material. An alternative is priming of the part surface to improve the wettability of the surface and protect it from oxidation. 

Fig. 1. Schematic preparation to obtain an ideal Si. (a) Oxide formation, (b) selective oxide stripping in HF. The surface is H-terminated with a structure which is close to the fingerprint of the Si/Si02 interface, (c) after subsequent chemical etching.

Fig. 1 Three different methods to pattern the CP layers. (A) Etching, e.g., using RIE A1 deposition of the patterned photoresist, A2 etching of the CP layer, A3 (wet chemical) etching of the metal layer, and finally A4 stripping of the photoresist. (B) Patterned electrodes Bl deposition of the patterned photoresist, B2 (wet chemical) etching of the metal layer, B3 stripping of the photoresist, B4 electrosynthesis of CP on the patterned metal electrode. (C) Resist holes Cl deposition of the patterned photoresist, C2 electrosynthesis of CP in the patterned photoresist layer, C3 stripping of the photoresist, C4 (wet chemical) etching of the metal layer, depending on the etchant a protective photoresist layer similar to A2 might be needed in this step...

Tin—Nickel. AHoy deposits having 65% fin have been commercially plated siace about 1951 (135). The 65% fin alloy exhibits good resistance to chemical attack, staining, and atmospheric corrosion, especially when plated copper or bron2e undercoats are used. This alloy has a low coefficient of friction. Deposits are solderable, hard (650—710 HV ), act as etch resists, and find use ia pfinted circuit boards, watch parts, and as a substitute for chromium ia some apphcafions. The rose-pink color of 65% fin is attractive. In marine exposure, tin—nickel is about equal to nickel—chromium deposits, but has been found to be superior ia some iadustfial exposure sites. Chromium topcoats iacrease the protection further. Tia-nickel deposits are bfitde and difficult to strip from steel. Temperature of deposits should be kept below 300°C. 

A characteristic of the group (a) of resins is that they air-dry solely by solvent evaporation and remain permanently solvent soluble. This fact, combined with the need to use strong solvents, makes brush application very difficult, but sprayed coats can be applied at intervals of one hour. A full vinyl system such as (o) possesses excellent chemical and water resistance. Many members of group (o) have very poor adhesion to metal, and have therefore been exploited as strip lacquers for temporary protection. Excellent adhesion is, however, obtained by initial application of an etching primer the best known of such primers comprises polyvinyl butyral, zinc tetroxy-chromate and phosphoric acid. 

From an IC manufacturing standpoint, two additional considerations fuel the drive toward dry etch processes. Relatively large volumes of dangerous acids and solvents must be handled and ultimately recycled or disposed of with wet etching or resist stripping techniques. Dry etching or resist stripping operations use comparatively small amounts of chemicals. 

FIGURE 2.3 Sequence for fabrication of the glass microfluidic chip, (a) Cr and Au masked glass plate coated with photoresist (b) sample exposed to UV light through a photomask (c) photoresist developed (d) exposed metal mask etched (e) exposed glass etched (f) resist and metal stripped (g) glass cover plate bonded to form sealed capillary [102]. Reprinted with permission from American Chemical Society. 

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