Printed-circuit cleaning boards

Apart from obvious dry cleaning applications, potential applications of C02-based microemulsions include (i) printed circuit board cleaning, (ii) extraction of contaminants from soils, (Hi) cleaning of polymers, foams, aerogels, porous ceramics, and laser optics, (iv) regeneration of activated carbon beds or catalysts, and (v) the separation of dyestuffs from textiles. 

Trichloroethane and other chlorinated solvents are used for vapor degreasing (84—90). Other uses include cold metal cleaning, printed ckcuit board cleaning, and as a solvent for inks, coatings, adhesives, and aerosols. 1,1,1-Trichloroethane is an excellent solvent for development of photoresist polymers used in printed ckcuit board manufacture (see Integrated circuits Photoconductivepolymers). 

Cleaning Supercritical fluids such as CO9 are being used to clean and degrease quartz rods used to produce optical fibers, produc ts used in the fabrication of printed circuit boards, oily chips from machining operations, and precision bearings in militaiy applications, and so on. Here, CO9 replaces convention chlorocarbon or chlorofluorocarbon solvents. 

Aqueous and semi-aqueous cleaning systems, used for printed circuit boards and other industrial degreasing operations (Mandich and Krulik, 1992 Davis et al., 1994)... 

Phosphates and phosphonates are valuable contents of cleaners used for technical purposes especially when anticorrosive behavior is also required. Phosphoric acid esters are a component of aqueous cleaning compositions for printed circuit boards [212]. 

Electronic cleaning Defluxing of printed circuit boards Soldering rosin... 

Finally, steps can also be taken to prevent the contaminant from ever entering the process. For example, the development of low-solids no clean rosin fluxes for soldering printed circuit boards completely eliminates the need for a cleaning process (Sapre, 1990). 

Trichlorotrifluoroethane (CFC 113) was widely used in the electronics industry for the removal of soldering flux residues from printed circuit boards, for degreasing components in the precision engineering industry, and for the dry cleaning of garments. 

Larger emissions or consumption of scarce resource could occur elsewhere in the lifecycle via the large-scale introduction of process intensification. For example, the proposed printed circuit board reactors could in the manufacturing step cause large emissions of VOCs from cleaning chemicals. And the demolition phase could... 

Electronics Industry Electronics-grade nitric acid (70%) is used by semiconductor and printed circuit board manufacturers. Nitric acid cleans contaminants from the wafer s surface during several steps in semiconductor manufacture. Acetic and hydrofluoric acids may be blended with nitric acid to etch away metal. Nitric acid is also used for cleaning in the manufacture of printed circuit boards. 

Removal of Heavy Metals. Federal, state and local regulations place strict limits on the quantities of heavy metals which may be released to the environment. The controlled metals include Ag, As, Cd, Cr, Cu, Pb, Hg, Ni, Sb and Zn. U.S. electroplaters, metal finishers, and printed-circuit-board manufacturers are under mounting pressure to clean up their waste waters. 

Alkanolamines are also used in formulations for removing photoresists (114,115) and cleaning printed-circuit boards (116). Formulations containing diethanolamine are used for electrodip coating of substrates (117). 

Aqueous and semi-aqueous cleaners are used primarily to clean printed-circuit boards prior to assembly, during application of the solder paste and adhesive (if they have been misprinted or smudged), and after assembly and solder reflowing. Highly automated multi-stage cleaning consoles are used in production where the parts are cleaned in a series of baths ending up with one or more deionized water rinses. 

Table 4.4 lists commercial cleaning solutions currently used in the electronics industry for cleaning printed-circuit boards, assemblies, ceramic printed circuits, thick-film interconnect substrates, electronic components, wiring harnesses, and stencils and screens (used in applying adhesives and solder pastes). 

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