CURE, screening process

After the initial screening process, it was necessary to develop model systems for both the carboxylate and alkoxide cured systems on which further experimentation could be performed. For the purposes of our testing,... 

UV curing inks frequently consist of 100% solids with no solvents (as used by screen processes). Since the use of UV creates some hazards (direct contact with UV and ozone residues), special equipment and precautionary procedures are essential. 

Screen Process This printing method has been previously discussed. Whether the drying of the inks is by heat or by UV curing, the screen process permits heavier deposits of ink laydown, and thus provides the greatest durability for outdoor use. 

When the diameter/thickness conditions are not met, it is necessary to fill the holes using a separate process. A screening process does this from one side of the panel with polyester screen with an oversized hole pattern. After hole filling and curing the resin completely, the fabricator removes excess resin using a belt sander ( 600 to 800) or a ceramic brush. Figure 22.16 illustrates the process.This is a tricky but necessary operation for microvia board makers, particularly for photovia processing. 

The static pile system is an intensive biotreatment because the pile of organic waste and bulking agent is intensively aerated using blowers and air diffusers. The pile is usually covered with compost to remove odor and to maintain high internal temperatures. The aerated static pile process typically takes 21 days, after which the compost is cured for another 30 days, dried, and screened to recycle the bulking agent. 

Radiometers for three-dimensional cure are used for simultaneous multipoint measurements, for setup and process verification of the lamp system. They can be used with UV lamps mounted on a fixed bank or a robotic arm. The collected exposure data (irradiance and total UV energy) are displayed on a computer for each sensor position. A SDCure radiometer is shown in Figure 9.7, and an example of a screen display from a 3D radiometer in Figure 9.8. 

Propellants. Satriana and Bracuti (Ref 30) claim the use of pyrolyzed urea as a ballistic modifier which when incorporated in a doublebase plastisol propint produces a burning rate plateau. Thus, PbSnC>3 (90) and urea, acet and w (10g) are sintered for one hr at 500—50°, cooled, screened, molded and cured for use in a plastisol proplnt contg 30% HMX. Leach (Ref 37) reports that ballistic and other test results indicate that there is no significant difference between M30 proplnt contg Nitroguanidine prepd by the urea/AN process and that prepd by the standard British fusion process. 

A recently reported alternative to spin or spray coating is screen printing of polyimide solutions (82, 85, 90). Screen printing is a low-cost, high-throughput process capable of directly patterning the polyimide films as they are deposited. Another alternative is the vapor deposition of polyimides, which was reported by researchers who co-evaporated the diamine and dianhydride monomers at stoichiometric rates (140). The evaporated films had better adhesion, a lower dielectric constant, and a lower dissipation factor compared with spin-coated polyimides. With this process, uniform, defect-free, conformal films can be cured in situ during deposition. 

The multilayer sensor structure consists of cermet and polymer based layers sequentially deposited on a 96% alumina ceramic substrate using a thick film screen printing process. The cermet layers are of ceramic-metal composition which require firing at a temperature of 850°C and the polymer layers are cured at temperatures below 100°C. Layout of this multilayer sensor structure is shown in Figure 1. 

Preform. A metal screen is made in the shape of the final product. Glass fiber is chopped 2 in. long and sprayed uniformly all over the shaped screen, using vacuum on the back side of the screen to assist the process. A small amount of binder, typically 5 percent of polymer in latex form, is sprayed onto the fiber to hold its shape. It is then removed from the screen, placed in the mold, saturated with an equal weight of liquid resin, and the mold is pressed at 1380 kPa (200 psi) and heated until cured, typically 3-15 min. This early process has been largely replaced by SMC. 

Ultraviolet light (UV) curable screen ink solder masks and photopolymerizable dry film solder masks have been available commercially since 1973 (5). These materials offer the PCB manufacturer many processing and production advantages relative to the conventional solvent-evaporative thermally cured solder masks. These products based on a new emerging technology have helped... 

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