Copper alloy substrate, plating

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). 

Electroplating of nickel can be performed on different substrate materials, among which the most usual are steel and copper alloys. For the nickel plating of steels in earlier years a layer of copper was first applied. At the present time the nickel coating is plated directly on the steel surface. A thin outer layer (0.3 pm) of chromium is applied over the nickel to keep the luster. Nickel is electrochemically nobler than steel in ordinary corrosion environment, e.g. salt water. Thus nickel does not give any cathodic protection at defects that penetrate the layer. For corrosion protection of steel the nickel layers therefore need to be free from defects. 

Low-force, low-voltage separable cormectors and contacts also have wide use in electronic systems [11,12], A variety of different configurations exist, but the substrate of most is made from copper, brass, bronze, or copper-beryllium. The use of copper alloys ensures some susceptibility to environmental degradation. To reduce interfacial resistance and corrosion, the substrate is plated with a nickel diffusion barrier and then with a precious metal (e.g., gold, palladium) [11,13], However, a trade-off exists between plating cost (thickness) and reliability [14]. Hence, physical defects (pores and cracks) are usually present. In the past, connectors and contacts could not be coated because of interference with their function, although some new coating inhibition formulations have been developed for this purpose [11,12]. 

Bronze, copper—tin alloy, electro deposits can be produced in thicker deposits using proprietary brightening additives in the plating solution, especially over a smooth bright substrate. The brightest deposit with better corrosion resistance is attained when bronze is plated over a bright nickel plate. However, direct plating over steel is not an uncommon practice. 

The formation of Cu-Sn alloy by galvanic contact deposition in the trimethyl-n-hexylammonium [bis(trifluoromethyl)sulfonyl]amide ([TMHAl TfiN ) ionic liquid at a temperature above 100 °C has been demonstrated by Katase et al. [41] Sn(II) was introduced into the liquid by dissolution of the SnflT N) salt which has a solubility of 0.2 mol dm f In the plating cell, a copper sheet was used as the cathodic substrate, a Sn sheet was used as the anode, and a Sn rod immersed in the same solution was used as a quasi-reference electrode. On short-circuiting, the Sn anode was oxidized to Sn(II) giving two electrons through external circuit to... 

Electroless plating — An autocatalytic process of metal deposition on a substrate by reduction of metal ions from solution without using an external source of electrons. It is promoted by specific reductants, namely formaldehyde, sodium hypophosphide, sodium boro-hydride, dialkylamine borane, and hydrazine. Electroless deposition has been used to produce different metal (e.g., nickel, cobalt, copper, gold, platinum, palladium, silver) and alloy coatings. It can be applied to any type of substrate including non-conductors. Some substrates are intrinsic catalytic for the electroless deposition other can be catalyzed usually by sensibilization followed by Pd nucleation also, in some non-catalytic metallic substrates the electroless process can be induced by an initial application of an appropriate potential pulse. In practical terms, the evaluation of the catalytic activity of a substrate for the electroless deposition of a given metal is... 

Methane sulfonic acid is used as an electrolyte for electroplating of tin onto sheet steel, for plating tin and tin/lead alloy onto nickel or other base metal substrates in the manufacture of lead frames and bump-contacts for microelectronic devices.It can also be used for copper deposition during the manufacture of microprocessors. Other alkanesulfonic acids have also found use in electroplating applications. Disodium methanedisulfonate and other alkanedisulfonate salts are used in chrome plating.As discussed previously, several processes for the recovery and recycle of alkanesulfonic acids from spent metal plating baths have been described. 

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