Masking defined

In this approach, a mask with desired geometry is inserted in the microscope to generate a mask-defined UV light beam projection on the monomer stream flowing in a polydimethylsiloxane (PDMS) microfluidics device described earlier. 

Copper plots may also be made by etching the kapton/copper laminate. This technology includes several steps of photosensitivity and etching. Electrochemical deposition of copper is made on the thin film of the kapton/constantan. The created bimetallic film is covered with a photosensitive resin, masked, and then subjected to ultraviolet exposure. This first mask defines the tracks (Fig. 19.6(a)). After development, the film... 

FIGURE 58.16 Solder-mask defined (SMD) and non-solder mask defined (NSMD) pad construction. For optimum reliability, the pad size on the PWB should be kept within 80 to 100 percent of the wetted pad area on the package side. This allows the stresses to be vectored equally between both ends of the solder joint, and it the PWB pad is slightly smaller, it allows a slightly higher stand off height, which also tends to enhance solder joint reliability. 

Effect of Package Pad Size on Joint-to-Board Strain. FEA can also been used to estimate the effect of changes in solder joint pad size on the joint-to-board strain ratio. Two different package pad sizes were nsed 0.53 mm, solder mask defined, (pad design 1) and 0.4 mm, solder mask defined, (pad design 2) while the PCB pad design was kept constant (0.5 mm, non-solder mask defined) The resnlts in terms of the joint-to-board strain at location 3 are shown in Fig. 59.23. 

For complex confining shapes, a different approach is required. In these cases, the surface shape can be introduced into the model by masking. Masking defines regions of the simulation volume that are inaccessible to the polymer film, creating the confining shape. The mask can be implemented as a geometric constraint, a space-fixed potential fidd, or a quantity of material (atoms or monomers) dther fixed or restrained... 

Solder Mask Technology (Material, Aperture Formation Methods) Pad Geometry Definition (Feature-Defined or Solder-Mask Defined)... 

FIG. 14 Pad geometry, a) non-solder mask defined and b) solder mask defined. 

FIG. 15 Crack propagation path for non-solder mask defined pad geometry. 

Figure C2.18.1. Schematic representation of various resuits of etching tiirough a mask. The regions marked by ietters are defined and described in tire text.

Dielectric Film Deposition. Dielectric films are found in all VLSI circuits to provide insulation between conducting layers, as diffusion and ion implantation (qv) masks, for diffusion from doped oxides, to cap doped films to prevent outdiffusion, and for passivating devices as a measure of protection against external contamination, moisture, and scratches. Properties that define the nature and function of dielectric films are the dielectric constant, the process temperature, and specific fabrication characteristics such as step coverage, gap-filling capabihties, density stress, contamination, thickness uniformity, deposition rate, and moisture resistance (2). Several processes are used to deposit dielectric films including atmospheric pressure CVD (APCVD), low pressure CVD (LPCVD), or plasma-enhanced CVD (PECVD) (see Plasma technology). 

Fig. 6. Schematic illustration of the photohthographic patterning process used for defining features in siUcon dioxide using ( ) a positive photoresist that polymerizes light, where ( ) represents the mask (U) Si02 and ( ) Si. Development includes removal of the mask and undeveloped photoresist.

Masking. Masking can be defined as the reduction of olfactory perception of a defined odor stimulus by means of presentation of another odorous substance without the physical removal or chemical alteration of the defined stimulus from the environment. Masking is therefore hyperadditive it raises the total odor level, possibly creating an overpowering sensation, and maybe defined as a reodorant, rather than a deodorant. Its end result can be explained by the simple equation of 1 + 1 = >2 (Fig. 2a). 

As with any other fabrication process, masks are needed to define the features to be etched. It is common that the etch used for the semiconductor also etches the masking material. For this reason many different masks are used in etching, including photoresist, dielectric films, and metals. Masking can be a complex issue, especially when very deep etches (>5 fim) are performed with high aspect ratios (148). 

Resists. Resists are temporary, thin coatings appHed to the surface of the copper-clad laminate. After patterning, these films act as masks that are chemically resistant to the cleaning, plating, and etching solutions used to define the circuit traces of the PWB. Both nonphotosensitive and photosensitive types are used. 

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