Copper electrical conductivity

Copper Electrical conductivity, thermal conductivity, thermal resistance... 

Although its electrical conductivity is only about 60% that of copper, it is used in electrical transmission lines because of its light weight. Pure aluminum is soft and lacks strength, but it can be alloyed with small amounts of copper, magnesium, silicon, manganese, and other elements to impart a variety of useful properties. 

Copper is reddish and takes on a bright metallic luster. It is malleable, ductile, and a good conductor of heat and electricity (second only to silver in electrical conductivity). 

Electrically Conducting Fibers. FlectricaHy conducting fibers are useful in blends with fibers of other types to achieve antistatic properties in apparel fabrics and carpets. The process developed by Nippon Sanmo Dyeing Co., for example, is reportedly used by Asahi in Casbmilon 2.2 dtex (2 den) staple fibers. Courtaulds claims a flame-resistant electrically conductive fiber produced by reaction with guanadine and treatment with copper sulfide (97). 

Impurities in cmde metal can occur as other metals or nonmetals, either dissolved or in some occluded form. Normally, impurities are detrimental, making the metal less useful and less valuable. Sometimes, as in the case of copper, extremely small impurity concentrations, eg, arsenic, can impart a harmful effect on a given physical property, eg, electrical conductivity. On the other hand, impurities may have commercial value. For example, gold, silver, platinum, and palladium, associated with copper, each has value. In the latter situation, the purity of the metal is usually improved by some refining technique, thereby achieving some value-added and by-product credit. 

In appUcations in which electrical conductivity is required, metals, copper, tungsten, molybdenum, and Kovar [12606-16-5] are the preferred chip-carrier materials. Metals have exceUent thermal conductivities. Tables 2 and 3 Ust the various materials used for substrates, along with their mechanical, electrical, and thermal properties. 

For many electronic and electrical appHcations, electrically conductive resias are required. Most polymeric resias exhibit high levels of electrical resistivity. Conductivity can be improved, however, by the judicious use of fillers eg, in epoxy, silver (in either flake or powdered form) is used as a filler. Sometimes other fillers such as copper are also used, but result in reduced efficiency. The popularity of silver is due to the absence of the oxide layer formation, which imparts electrical insulating characteristics. Consequently, metallic fibers such as aluminum are rarely considered for this appHcation. 

Copper is by far the most widely used conductor material. It has high electrical conductivity, thermal conductivity, solderabiUty, and resistance to corrosion, wear, and fatigue. Annealed copper conductors can withstand flex and vibration stresses normally encountered in use. 

A 99.5% Cu—0.5% Te alloy has been on the market for many years (78). The most widely used is alloy No. CA145 (number given by Copper Development Association, New York), nominally containing 0.5% tellurium and 0.008% phosphorous. The electrical conductivity of this alloy, in the aimealed state, is 90—98%, and the thermal conductivity 91.5—94.5% that of the tough-pitch grade of copper. The machinahility rating, 80—90, compares with 100 for free-cutting brass and 20 for pure copper. 

Zinc—bromine storage batteries (qv) are under development as load-leveling devices in electric utilities (64). Photovoltaic batteries have been made of selenium or boron doped with bromine. Graphite fibers and certain polymers can be made electrically conductive by being doped with bromine. Bromine is used in quartz—haUde light bulbs. Bromine is used to etch aluminum, copper, and semi-conductors. Bromine and its salts are known to recover gold and other precious metals from their ores. Bromine can be used to desulfurize fine coal (see Coal conversion processes). Table 5 shows estimates of the primary uses of bromine. 

Figure 12 contrasts the decrease in conductivity of ETP copper with that of oxygen-free copper as impurity contents are increased. The importance of oxygen in modifying the effect of impurities on conductivity is clearly illustrated. Phosphoms, which is often used as a deoxidizer, has a pronounced effect in lowering electrical conductivity in oxygen-free copper, but Httie effect in the presence of excess oxygen. 

Strength. Tensile properties and electrical conductivities of selected copper alloys having commercial importance are Hsted in Table 5. The principal source of strengthening and the individual product forms in which each alloy is usually available are also identified. 

Electrical—Thermal Conductivities. Electrical conductivities of alloys (Table 5) are often expressed as a percentage relative to an International Annealed Copper Standard (lACS), ie, units of % lACS, where the value of 100 % lACS is assigned to pure copper having a measured resistivity value of 0.017241 Q mm /m. The measurement of resistivity and its conversion to % lACS is covered under ASTM B193 (8). 

Copper has a high electrical conductivity that is second only to that of silver. The conductivity of silver in % lACS units is 108 gold, 73 aluminum, 64 and iron, 18. Wrought copper having a conductivity near 102% lACS is not uncommon because of improvements in refining practices since the standard was first estabUshed. 

Electrical conductivity of copper is affected by temperature, alloy additions and impurities, and cold work (9—12). Relative to temperature, the electrical conductivity of armealed copper falls from 100 % lACS at room temperature to 65 % lACS at 150°C. Alloying invariably decreases conductivity. Cold work also decreases electrical conductivity as more and more dislocation and microstmctural defects are incorporated into the armealed grains. These defects interfere with the passage of conduction electrons. Conductivity decreases by about 3—5% lACS for pure copper when cold worked 75% reduction in area. The conductivity of alloys is also affected to about the same degree by cold work. 

Copper and its alloys also have relatively good thermal conductivity, which accounts for thek appHcation where heat removal is important, such as for heat sinks, condensers, and heat exchanger tubes (see Heatexchangetechnology). Thermal conductivity and electrical conductivity depend similarly on composition primarily because the conduction electrons carry some of the thermal energy. 

To a good approximation, thermal conductivity at room temperature is linearly related to electrical conductivity through the Wiedemann-Eran2 rule. This relationship is dependent on temperature, however, because the temperature variations of the thermal and the electrical conductivities are not the same. At temperatures above room temperature, thermal conductivity of pure copper decreases more slowly than does electrical conductivity. Eor many copper alloys the thermal conductivity increases, whereas electrical conductivity decreases with temperature above ambient. The relationship at room temperature between thermal and electrical conductivity for moderate to high conductivity alloys is illustrated in Eigure 5. 

Resistance welding has been successfully appHed to copper alloys in all of its various spot, seam, or butt joining modes. Because the process depends on ohmic (l R) heating at the interface to be joined, the abiHty to resistance weld is inversely related to electrical conductivity of the alloys being welded. 

Trace elements added to copper exert a significant influence on electrical conductivity. Effects on conductivity vary because of inherent differences ia effective atomic size and valency. The decrease ia conductivity produced by those elements appearing commonly ia copper, at a fixed atomic concentration, rank as follows Zn (least detrimental), Ag, Mg, Al, Ni, Si, Sn, P, Fe (most). Table 12 summarizes these effects. In the absence of chemical or physical interactions, the increase in electrical resistivity is linear with amounts of each element, and the effect of multiatom additions is additive. 

Table 12. Solubility Limits and Electrical Conductivity Effects of Elemental Additions to Copper ...

Commercial precipitation hardening copper alloys are based on beryUium, chromium, and nickel, this last in combination with siUcon or tin. The principal attributes of these alloys are high strength in association with adequate formabiUty. Electrical conductivity varies according to alloy and ranges from around 20 to 80% lACS. 

Typical properties of these alloys are shown in Table 25. In addition, these alloys exhibit notably excellent resistance to stress relaxation at high appHcation temperatures, for instance 200°C, and in this respect outperform beryUium—copper. However, the electrical conductivity of the strongest Cu—Ni—Sn composition (C729) is lower than that of C172. 

The thermal conductivity of copper having an electrical conductivity of 100% lACS is 391 W/ (m-K) at 20°C. The Wiedemann-Eranz ratio of thermal conductivity and the product of electrical conductivity times absolute temperature are approximately constant. Many copper alloys have increasing thermal conductivity with increase in temperature, whereas electrical conductivity decreases. 

Electrical conductivity is comparatively easy to measure, whereas thermal conductivity is not. Electrical conductivity values for the important cast alloys are Hsted in Table 2. Eigure 1 schematically shows the electrical conductivity of cast copper-base alloys compared with various other cast metals and alloys. The equation Y = 4.184 + 3.93a gives an approximation of thermal conductivity in relation to electrical conductivity, where Tis in W/(m-K) at 20°C and X is the % lACS at 20°C. 

Chromium. Chromium [7440 7-3] also forms heat-treatable copper ahoys. These ahoys, in the heat-treated condition, have a Brinell hardness of about 120 and an electrical conductivity of about 80% lACS. 

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