Undercut resist

Zinc primer provides outstanding corrosion resistance and undercutting resistance. A barrier protection for the zinc primer is provided by the finish coat of epoxy which aiso provides a coior coat for appearance. Suitabie for use on carbon steei oniy. 

Zinc primer provides outstanding corrosion resistance and undercutting resistance. Water based single package finish has excellent weathering and semigloss appearance. 

Resins are also used for permanent tooth-colored veneers on fixed prostheses, ie, crown and bridges. Compositions for this application include acryflcs, vinyl—acryflcs, and dimethacrylates, as well as silica- or quartz-microfilled composites. The resins are placed on the metallic substrates of the prostheses and cured by heat or light. These resins are inexpensive, easy to fabricate, and can be matched to the color of tooth stmcture. Acrylic facings do not chemically adhere to the metals and are retained only by curing the resin into mechanical undercuts designed into the metal substrate. They have relatively low mechanical strength and color stability, and poor abrasion and strain resistance they also deform more under the stress of mastication than porcelain veneers or facings. 

A major advantage of the electroless nickel process is that deposition takes place at an almost uniform rate over surfaces of complex shape. Thus, electroless nickel can readily be applied to internal plating of tubes, valves, containers and other parts having deeply undercut surfaces where nickel coating by electrodeposition would be very difficult and costly. The resistance to corrosion of the coatings and their special mechanical properties also offer advantages in many instances where electrodeposited nickel could be applied without difficulty. 

Figure 5. Undercutting corrosion resistance of enameled plate...

Figure 13a shows the resist in a three-layer Al-RIE-PCM system by Havas et al. The dry etching conditions were similar to those of plasma etching. Therefore, an undercut was produced under the Al PCM to facilitate lift-off. Figure 13b shows the resist image in a three-layer siloxane RIE PCM system. The dry etching process was sufficiently anisotropic to eliminate the undercut. 

With many of the Union Carbide organosilanes investigated, it was difficult to distinguish which materials worked best on freshly 1050°C steam-oxidized (1 m) wafers. Wafers were therefore intentionally soaked in water for 48 h, spun dry , followed by the addition of the organosilane (100%) to the substrate at 3000 rpm for 10 s. The negative resist (1 fim) coated wafers were patterned and processed in a conventional manner, and the oxide was etched in 4 1 buffered NH4F-HF at room temperature until the oxide was removed. Examination (by microscope) of the resist surface for resist lift, followed by resist strip to observe undercutting was performed. 

Aluminum powder, in particular, is frequently employed at relatively high concentrations in high-temperature epoxy adhesive formulations. The filler provides improvement in both tensile strength and heat resistance, and it increases the thermal conductivity of the adhesive. Aluminum powder fillers also reduce undercut corrosion and, hence, improve adhesion and durability of epoxy adhesive between bare steel substrates. It is believed that this is accomplished by the aluminum filler providing a sacrificial electrochemical mechanism.27... 

Figure 2.4. The latent image in the resist has essentially the shape indicated because of the sloping nature of the free space image and the absorption of the resist film. Depending on the processing conditions, either negatively sloped undercut profiles) vertical profiles or positively sloped profiles can be obtained.

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