Printed Circuit Board corrosion

Because the heat distortion temperature of cured epoxy resins (qv) increases with the functionality of the curing agents, pyromellitic dianhydride is used to cross-link epoxy resins for elevated temperature service. The dianhydride may be added as a dispersion of micropulverized powder in liquid epoxy resin or as a glycol adduct (158). Such epoxies may be used as an insulating layer in printed circuit boards to improve heat resistance (159). Other uses include inhibition of corrosion (160,161), hot melt traffic paints (162), azo pigments (163), adhesives (164), and photoresist compounds (165). 

The contact ends of printed circuit boards are copper. Alloys of nickel and iron are used as substrates in hermetic connectors in which glass (qv) is the dielectric material. Terminals are fabricated from brass or copper from nickel, for high temperature appHcations from aluminum, when aluminum conductors are used and from steel when high strength is required. Because steel has poor corrosion resistance, it is always plated using a protective metal, such as tin (see Tin and tin alloys). Other substrates can be unplated when high contact normal forces, usually more than 5 N, are available to mechanically dismpt insulating oxide films on the surfaces and thereby assure metaUic contact (see Corrosion and corrosion control). 

The significance of corrosion protection has risen sharply in recent years for a number of reasons (1) because of efforts to reduce the metal content of parts (e.g., by using thinner metallic support structures) (2) with the use of new types of equipment and processes involving expensive equipment operated under extreme conditions, such as nuclear reactors and jet and rocket engines and (3) in connection with the development of products having extremely thin metal films, such as printed circuit boards and integrated circuits. 

Tin—Nickel, Alloy deposits having 65% tin have been commercially plated since about 1951 (135). The 65% tin alloy exhibits good resistance to chemical attack, staining, and atmospheric corrosion, especially when plated copper or bronze undercoats are used. This alloy has a low coefficient of friction. Deposits are solderable, hard (650—710 HV 5Q), act as etch resists, and find use in printed circuit boards, watch parts, and as a substitute for chromium in some applications. The rose-pink color of 65% tin is attractive. In marine exposure, tin—nickel is about equal to nickel—chromium deposits, but has been found to be superior in some industrial exposure sites. Chromium topcoats increase the protection further. Tin—nickel deposits are brittle and difficult to strip from steel. Temperature of deposits should be kept below 300°C. 

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). 

Even after production of printed circuit boards and semiconductor components, ion chromatography may be taken advantage of. Malfunctions are often caused by corrosive anions on the surface of printed circuits or inside, where the microchips are imbedded. Identification and quantification of these compounds with the aid of ion chromatographic techniques often represents a significant contribution for localizing the sources... 

ISO 11907-. 3 [122] consists of a tube furnace and quartz lube similar to that of DIN 53436 [III]. The te.st specimen is placed in a boat and the hot furnace (600 C) traversed along it. Air flows through the furnace tube and over the corrosivity detector, which consists of an etched copper printed circuit board. The printed circuit board is cooled to 10 C to cause the corrosive vapors to condense. The corrosivity is expressed as the percentage change in resistance relative to the original value. 

Printed circuit boards that are operated in an aggressive environment need special corrosion protection. A particularly acute need exists in commercial utility meters, such as natural gas meters, water meters, or electric meters. In addition, there may be the demand for repair and reapplication... 

Uses Corrosion inhibitor tor copper, high copper alloys for use in aq. systems, printed circuit boards, metalworking fluids, water treatment, air conditioning fluids, engine coolants Features Noncaustic nondusting nontlamm. 

Chem. Descrip. Glycerin-1-allylether CAS 123-34-2 EINECS/ELINCS 204-6204 Uses Can be polymerized into polyesters, polyurethanes, polyacetals, and epoxy resins (hydroxyl group) or with acrylates, methacrylates, or styrene (ilyl group) for prod, of PL) rubber and foam printed circuit boards unsat. polyesters used for radiation-resist, coatings copolymers as dispersants for pigments or as corrosion inhibitors Properties Colorless to yish. vise, liq., perceptible odor sol. in water, ethanol, and many org. soivs. dens. 1.07 g/cc vapor pressure 0.004 mbar (20 C) m.p. < C b.p. 245 C (decomp.) flash pt. 135 C pH 7 (5% aq.) 9 /o assay... 

Uses Binder, film-former in paints (printed circuit board coatings, coil, container, conosion-protection, marine, metal, plastics, sealers, tarp, wood varnishes), printing inks (screen printing), primers (adhesion pro-motion/corrosion protection), ceramic compds., sealers, heat-sealable lacquers, two-pack paints, resinous/polymeric food-contact coatings reactive resin in two-pack systems, e.g., crosslinked with melamine/phenolic resins... 

Nickel deposits are most widely used as a base for chromium plating the thicker the deposit (typically 20 xm), the greater the corrosion resistance. Nickel plating is used in engineering where wear resistance, hardness and corrosion resistance are required, e.g. oil valves, rotors, drive shafts and in printed circuit board manufacturer. It is also used for its decorative properties, e.g. doorknobs. 

Uses Corrosion inhibitor for copper, brass, steel, aluminum, and zinc for use in printed circuit boards, circulating water systems, air conditioning systems, steam generators, refrigeration systems, cooling towers, engine jackets and pipes... 

Applications like corrosion protection by ennobling and passivation, and manufacture of printed circuit board surfaces composed of the organic metal polyaniline (Ormecon) are based exclusively on this unique set of properties and use most of the properties in parallel. Here, this new materials class is able to offer a performance that cannot be matched by any other material or by another conductive polymer. 

To realize this performance, commercial products are actually being introduced into the market. A review by Miller [66] is still relatively accurate, except for significant technical and market progress in transparent coatings (Section 1.3.2.1), corrosion protection (Section 1.3.2.2), and printed circuit board... 

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