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Plating Information
Electroplating is the process of putting a metallic coating on a metal or other conducting surface by using an electric current. It is used to improve the appearance of materials, for protection against corrosion, and to make plates for printing.
The article to be plated is thoroughly cleansed of grease and dirt by dipping it in acid and alkaline cleaning solutions. It is then put in a solution of the metal with which it is to be coated. The metal exists in the form of positive ions (atoms that have lost one or more electrons). The article is connected to the cathode (negative end of a source of electricity). The anode (positive electric terminal) is connected to another conductor, which is also dipped into the solution. The electric current acts on the metallic ions in the solution. The ions are attracted to the cathode, and the coating is deposited on the article's metal surface. If the metal in the solution and the metal of the positive terminal are the same, the electricity may remove metal from the terminal to replace metal taken from the solution.
The thickness of the layer deposited on the article depends on the strength of the electric current, the concentration of metallic ions, and the length of time the article has been in the solution. The terms triple-plated and quadruple-plated indicate various thicknesses of plating, not separate layers deposited on the surface.
Ornamental and protective platings are very thin, usually from one to two thousandths of an inch (0.03 to 0.05mm) thick. For plating gold, silver, copper, zinc, and cadmium, cyanide solutions of the same metals are often used. Copper and zinc may also be plated by acid-sulfate solutions. Alloys of two or more metals may be deposited by using a solution of salts of the metals that make up the alloy.
Examples of alloys used for plating are brass, black nickel, lead-tin, and bronze. |
Copper and Copper Alloys:
Copper and copper alloy wires are often electroplated with precious metal coatings. The coating may be singular, such as silver-plated copper or may be of multiple layers, such as nickel-gold or nickel-palladium-gold plated copper alloy wire. The performance characteristics of pure precious metal deposits can be enhanced with alloying additives. For example, nickel or cobalt can be added to gold to produce a "hard" gold surface.
One of the main attributes of copper alloys is their high electrical and thermal conductivity, making these alloys quite attractive in electrical and electronic applications. With a steady move toward miniaturization, alloys with high electrical conductivity at the same strength levels are required. The addition of alloying elements to improve various properties of copper, such as strength, reduces electrical conductivity. When added to copper as an alloying addition, each element and combination of various elements influences electrical conductivity in different ways. High performance alloys have been designed to provide high strength with a lesser reduction in electrical conductivity of elemental copper.
The following is a description of some copper alloys:
Nickel silvers - Nickel silvers are alloys that contain copper, nickel and zinc. The term nickel silver refers to their attractive silver luster. Nickel silvers have moderately high strength and good corrosion resistance.
Beryllium - Beryllium copper is a precipitation-hardening alloy containing about 2% beryllium in copper. The combined properties of beryllium/copper alloys often prove it to be the most economical for a given application. These alloys combine the very high physical characteristics of some sophisticated stainless steels with the qualities of copper alloys. Some characteristics are the following
o High fatigue strength
o Unusual wear resistance
o High corrosion resistance
o High tensile strength
o Elasticity
o High electrical and thermal conductivity
o Good formability
o Excellent properties at elevated temperatur
Beryllium copper is the strongest and best spring material among all copper alloys for application in high temperature, high corrosive and high electrical current environment. It is the best choice for micro-switch, connector, terminal, relay and high precision spring parts. Beryllium copper may be plated with gold or tin.
Phosphor bronze - Phosphor bronzes or tin bronzes are alloys containing copper, tin and phosphorous. The phosphor bronzes contain between 0.5 and 11% tin and 0.01 to 0.35% phosphorous. The addition of tin increases the corrosion resistance and strength of the azes have excellent spring qualities, high fatigue resistance, excellent formability and solderability, and high corrosion resistance. Tin-plated phosphor bronze is used in electronics and in RFI shielding.
Nickel - Copper nickel alloys contain from 2 to 30% nickel, depending upon the application. These alloys may have iron, chromium, niobium, and or manganese added to improve the strength and corrosion resistance. These alloys are thermally stable and very corrosion resistant. They have high oxidation resistance in steam and moist air. They have moderate strength even at elevated temperatures. Higher nickel alloys are corrosion-resistant in seawater and are resistant to marine bio-fouling.
Copper alloy wire is available in a variety of shapes, tailor made to customer-specified size and tolerances: round, square, rectangular, flat, and special. Square or rectangular wire shapes are specified by defining two of three variables: size, corner radii, or diagonals. Special features such as crowned surfaces may be specified in square or rectangular wire. Flat wire edges are usually free formed but may be shaped to specification.
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Plating for Copper and Copper Alloys:
Silver - Silver is quite soft and malleable (easily shaped).. With the exception of gold, it is the most malleable and ductile (able to be drawn into very thin wire) of all metals. Silver is harder than gold but softer than copper. It is quite resistant to corrosion and does not oxidize easily. Of all the metals, it is the best conductor of electricity. When silver is plated over copper there can be an accelerated corrosion of the copper at pinholes or breaks in the silver plating. It is then susceptible to the formation of cuprous oxide when stored or used in a moist or high humidity environment. The corrosion is known as "red plague" and is identifiable by the presence of a brown-red powder deposit on the exposed copper. Due to this possible corrosion, it may be wise to consider an insulation over the silver-plated copper wire, such as Teflon. Silver plated copper has applications in the medical field. Silver plating over oxygen-free copper reduces the resistance of the copper, thus enhancing audio and video cables and wires.
Gold - Gold is soft and wears easily, so it is often mixed with harder metals. Gold is un-reactive, which means it is resistant to corrosion and tarnishing, at high or low temperatures. Gold is also malleable and ductile. Gold is a very good conductor of electricity and, since it can be drawn into very thin wires, has many applications in electronics. Gold plating on contacts for switches, relays and connectors accounts for most of the gold required each year by the electronics industry. Gold is used in satellites as part of their electronic circuits and as a heat shield. Copper with gold or silver plating can be used in the ultra flexible and ultra miniature wire needed in instrumentation used in the medical industry.
Tin - The properties of tin make it ideal for use as a coating. Tin has a low melting point and readily alloys with most other metals, so tin coatings can be easily produced by immersing a suitable prepared metal object in a bath of molten tin. Hot-dipped tin coatings present a good appearance and are tightly adherent. When coated sheets are severely drawn and worked, the coating actually acts as a lubricant. Tin coatings may also be produced by electroplating the metal from an aqueous solution of its salts. Copper tin alloys or tin bronzes are known for their corrosion resistance. Tin bronzes are stronger and more ductile than red and semi-red brasses. They have high wear resistance and low friction coefficient against steel. Tin-nickel is highly resistant to corrosion and tarnish, and is therefore used in electrical equipment and scientific instruments.
Copper and nickel may both be used as plating over other metals.
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Plating for Aluminum:
Copper clad aluminum has applications in the medical, electronics, and communications industries, as well as being used in RFI (radio frequency interference) shielding.
Plating for Steel:
Tin - plated copper clad - This has applications in the electronics and communications industries, and is also used in RFI (radio frequency interference) shielding.
Silver - plated copper clad - used in the communications industry.
Gold - plated stainless steel
Nickel - plated steel is used in the communications and electronic industries |
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