Printed-circuit board contaminant

The etched printed circuit boards are washed out with water to dilute the concentration of the contaminants on the board surface to an acceptable level. The extraction of copper from the effluent rinse water is essential for both environmental and economic reasons since decontaminated water is returned to the rinse vessel. 

In a printed circuit board etching line using copper(II) chloride solution, 45 wt% hydrogen peroxide solution was used to recover the copper salts. The peroxide header tank became contaminated with trace amounts of the etching solution, and catalytic decomposition of the peroxide led to a pressure burst of the tank. 

Maryland Supeifund Site Natural attenuation enabled new development at 70-acre Superfund site approximately 20 miles northwest of Baltimore, Maryland. This property had been contaminated by a printed circuit board manufacturing company. According to a manager, the pump-and-treat remediation system failed to meet groundwater treatment goals, though it cost over 1 million to construct and more than 200,000 a year to operate. It was estimated that this approach could cost as much as 5 million over 10 years and would still not achieve the cleanup objectives of the Maryland Department of Environment (D17452R). 

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). 

Microspectroscopy applies the identification power of infrared spectroscopy to the microscopic realm. Contaminants on printed circuit boards, blemishes in coatings, and other production defects can be isolated in situ and analyzed (see Electronics, coatings). Analysis of flaws that develop during use illuminates the method of failure. Microscopic samples, such as particulates filtered from air, can be analyzed individually. The forensic applications are many paint chips, single fibers, explosive residues, and inks on currency can all be identified nondestmctively (see Forensic chemistry). The structures of layered materials, such as laminated polymer films, are studied via microspectroscopy by cross-sectioning the materials and examining the individual layers edge on (47). 

Electrical intermittents caused by poor contacts of printed circuit boards (PCBs) is a major source of problems for navigational computers used on nuclear submarines. The cause of the intermittencies has been traced to the presence of dirt, tarnish, corrosion products and organic contaminants accumulating at the pin connector junctions (50). 

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. 

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. 

Solder masks (solder resists) are protective polymer coatings used on printed circuit boards (PCB s) to prevent solder bridging between conductors during soldering (1-3). The selective application of the solder mask limits the amount of conductor area in contact with the molten solder, minimizing solder usage and slowing the rate of conductor metal contamination in the solder pot. 

Degreasing electronics and printed-circuit boards, ionic contaminant removal... 

Abzol VG, EG, and JEG/ Albemarle Alkyl bromide mixture Degreasing electronics and printed-circuit boards, ionic contaminant removal 125 70-71 25.9 58.8 None 138... 

This is the removal of oil, grease or other contaminants from the surface of metals, and increasingly plastic components and assemblies. Substrates cleaned include mild steel, brass, copper, polypropylene and printed circuit boards, the level of cleanliness required depending on the application. 

Electronics are exposed to a wide range of outdoor and indoor environments generally considered as atmospheric exposure. The corrosion behavior is determined by the actual environment, which can be as benign as a simple low humidity, purified atmosphere, indoor location, to the aggressive environment existing at a pulp and paper mill or on an automobile, which is subjected to road salt splash and spray. The electronics design as well as the nature of the environment are important because failures in printed circuit boards, integrated circuits, and other components have been known to occur even in extremely low levels of moisture and contaminants. Electronics components are mostly indoor or sheltered from direct exposure to liquid splash, spray, rain, snow, etc., and therefore the environment is considered atmospheric exposure. 

Electrochemical Failure Modes. The primary function of a printed circuit board is to provide electrical connections with the desired, stable, low-impedance and high-impedance insulation between them. A high surface insulation resistance (SIR) value is usually assumed by the circuit designer. Exposure to humidity, especially when ionic contaminants are present, is a common cause of insulation resistance failures that is accelerated by elevated temperatures and electrical bias. The impedance often decreases slowly over a long period of time. If the SIR value falls below the designed level, there will be cross talk between circuit elements that should be isolated, and the circuit may not function properly. Insulation... 

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