Background

Copper is the oldest metal used by man. It’s use dates back to prehistoric times. Copper has been mined for more than 10,000 years with a Copper pendant found in current day Iraq being dated to 8700BC. By 5000BC Copper was being smelted from simple Copper Oxides. Copper is found as native metal and in the minerals cuprite, malachite, azurite, chalcopyrite and bornite. It is also often a by-product of silver production. Sulphides, oxides and carbonates are the most important ores. Copper and Copper alloys are some of the most versatile engineering materials available. The combination of physical properties such as strength, conductivity, corrosion resistance, machinability and ductility make copper suitable for a wide range of applications. These properties can be further enhanced with variations in composition and manufacturing methods. Building Industry The largest end use for Copper is in the building industry. Within the building industry the use of copper based materials is broad. Construction industry related applications for copper include: · Roofing · Cladding · Rainwater systems · Heating systems · Water pipes and fittings · Oil and gas lines · Electrical wiring The building industry is the largest single consumer of copper alloys. The following list is a breakdown of copper consumption by industry on an annual basis: · Building industry – 47% · Electronic products - 23% · Transportation - 10% · Consumer products - 11% · Industrial machinery - 9% Commercial Compositions There are around 370 commercial compositions for copper alloys. The most common grade tends to be C12200 - the standard water tube grade of copper. World consumption of copper and copper alloys now exceeds 18 million tonnes per annum.

Applications

Copper and copper alloys can be used in an extraordinary range of applications. Some of these applications include: · Power transmission lines · Architectural applications · Cooking utensils · Spark plugs · Electrical wiring, cables and busbars · High conductivity wires · Electrodes · Heat exchangers · Refrigeration tubing · Plumbing · Water-cooled copper crucibles Structure Copper has a face centred cubic crystal structure. It is yellowish red in physical appearance and when polished develops a bright metallic lustre. Key Properties of Copper Alloys Copper is a tough, ductile and malleable material. These properties make copper extremely suitable for tube forming, wire drawing, spinning and deep drawing. The other key properties exhibited by copper and its alloys include: · Excellent heat conductivity · Excellent electrical conductivity · Good corrosion resistance · Good biofouling resistance · Good machinability · Retention of mechanical and electrical properties at cryogenic temperatures · Non-magnetic Other Properties · Copper and Copper alloys have a peculiar smell and disagreeable taste. These may be transferred by contact and therefore Copper should be kept clear of foodstuffs. · Most commercially used metals have a metallic white colour. Copper is a yellowish red. Melting Point The melting point for pure copper is 1083ºC. Electrical Conductivity The electrical conductivity of copper is second only to silver. The conductivity of copper is 97% that of silver. Due to its much lower cost and greater abundance, copper has traditionally been the standard material used for electricity transmission applications. However, weight considerations mean that a large proportion of overhead high voltage power lines now use aluminium rather than copper by weight, the conductivity of aluminium is around twice that of copper. The aluminium alloys used do have a low strength and need to be reinforced with a galvanised or aluminium coated high tensile steel wire in each strand. Although additions of other elements will improve properties like strength, there will be some loss in electrical conductivity. As an example a 1% addition of cadmium can increase strength by 50%. However, this will result in a corresponding decrease in electrical conductivity of 15%. Corrosion Resistance All Copper alloys resist corrosion by fresh water and steam. In most rural, marine and industrial atmospheres Copper alloys also resistant to corrosion. Copper is resistant to saline solutions, soils, non-oxidising minerals, organic acids and caustic solutions. Moist ammonia, halogens, sulphides, solutions containing ammonia ions and oxidising acids, like nitric acid, will attack Copper. Copper alloys also have poor resistance to inorganic acids. The corrosion resistance of Copper alloys comes from the formation of adherent films on the material surface. These films are relatively impervious to corrosion therefore protecting the base metal from further attack. Copper Nickel alloys, Aluminium Brass, and Aluminium Bronzes demonstrate superior resistance to saltwater corrosion. Surface Oxidation of Copper Most Copper alloys will develop a blue-green patina when exposed to the elements outdoors. Typical of this is the colour of the Copper Statue of Liberty in New York. Some Copper alloys will darken after prolonged exposure to the elements and take on a brown to black colour. Lacquer coatings can be used to protect the surface and retain the original alloy colour. An acrylic coating with benzotriazole as an additive will last several years under most outdoor, abrasion-free conditions. Yield Strength The yield point for Copper alloys is not sharply defined. As a result it tends to be reported as either a 0.5% extension under load or as 0.2% offset. Most commonly the 0.5% extension yield strength of annealed material registers as approximately one-third the tensile strength. Hardening by cold working means the material becomes less ductile, and yield strength approaches the tensile strength. Joining Commonly employed processes such as brazing, welding and soldering can be used to join most copper alloys. Soldering is often used for electrical connections. High Lead content alloys are unsuitable for welding. Copper and Copper alloys can also be joined using mechanical means such as rivets and screws. Hot and Cold Working Although able to be work hardened, Copper and Copper alloys can be both hot and cold worked. Ductility can be restored by annealing. This can be done either by a specific annealing process or by incidental annealing through welding or brazing procedures. Temper Copper alloys can be specified according to temper levels. The temper is imparted by cold working and subsequent degrees of annealing. Typical tempers for Copper alloys are · Soft · Half-hard · Hard, spring · Extra-spring Yield strength of a hard-temper Copper alloy is approximately two-thirds of the materials’ tensile strength. Copper Designations Designation systems for Copper are not specifications, but methods for identifying chemical compositions. Property requirements are covered in ASTM, government and military standards for each composition. The method for designating Copper alloys is an expansion upon the system developed by the U.S. copper and brass industry. Their old system used 3 digits, the new Unified Numbering System for Metals and Alloys (UNS) system uses five digits preceded by the letter C. As an example the forging brass known as Copper alloy 377 is known as C37700 under the UNS system. Wrought compositions are included in the designations from C10000 through to C79900. Casting alloys are assigned numbers from C80000 through to C99900 The UNS designations are summarised in the following table: UNS Numbers Types Alloy Names C10000-C19999 Wrought Coppers, High-Copper Alloys C20000-C49999 Wrought Brasses C50000-C59999 Wrought Phosphor Bronzes C60600-C64200 Wrought Aluminium Bronzes C64700-C66100 Wrought Silicon Bronzes C66400-C69800 Wrought Brasses C70000-C79999 Wrought Copper nickels, nickel silvers C80000-C82800 Cast Coppers, High-Copper Alloys C83300-C85800 Cast Brasses C86100-C86800 Cast Manganese Bronzes C87200-C87900 Cast Silicon Bronzes and Brasses C90200-C94800 Cast Tin Bronzes C95200-C95800 Cast Aluminium Bronzes C96200-C97800 Cast Copper Nickels, Nickel Silvers C98200-C98800 Cast Leaded Copper C99300-C99750 Cast Special Alloys

Cast Copper Alloys The nature of the casting process means that most cast Copper alloys have a greater range of alloying elements than wrought alloys. Wrought Copper Alloys Wrought copper alloys are produced using a variety of different production methods. These methods including processes such as annealing, cold working, hardening by heat treatments or stress relieving. Copper Alloy Families Within the wrought and cast categories for Copper alloys, the compositions can be divided into the following main families: · Pure Coppers · High Copper Alloys · Brasses · Bronzes Coppers The Pure Coppers have a Copper content of 99.3% or higher. High Copper Alloys Wrought high Copper alloys have Copper contents of less than 99.3% but more than 96% but don’t fall into another Copper alloy group. Cast high Copper alloys have Copper contents in excess of 94%. Silver may be added to impart special properties. Brasses Brasses contain Zinc as the principal alloying element. Other alloying elements may also be present to impart advantageous properties. These elements include Iron, Aluminium, Nickel and Silicon. Brasses are most commonly characterised by their free machining grades by which machining standards are set for all other metals. Brasses can also have high corrosion resistance and high tensile strength. Some brasses are also suited to hot forging. Brass Additives Adding Lead to a brass composition can result in a brass with the ability to be rapidly machined. It will also produce less tool wear. Adding Aluminium, Iron and Manganese to brass improves strength. Silicon additions improve wear resistance. Brasses are divided into two classes and three families. Brass Classes Brasses are divided into two classes. These are: · The alpha alloys, with less than 37% Zinc. These alloys are ductile and can be cold worked. · The alpha/beta or duplex alloys with 37-45% Zinc. These alloys have limited cold ductility and are typically harder and stronger. Brass Families There are three main families of wrought alloy brasses: · Copper-Zinc alloys · Copper-Zinc-Lead alloys (Leaded brasses) · Copper-Zinc-Tin alloys (Tin brasses) Cast brass alloys can be broken into four main families: · Copper-Tin-Zinc alloys (red, semi-red and yellow brasses) · Manganese Bronze alloys (high strength yellow brasses) and Leaded Manganese Bronze alloys (leaded high strength yellow brasses) · Copper-Zinc-Silicon alloys (Silicon brasses and bronzes) · Cast Copper-Bismuth and Copper-Bismuth-Selenium alloys. Bronzes The term bronze originally described alloys with Tin as the only or principal alloying element. Modern day bronzes tend to be Copper alloys in which the major alloying element is not Nickel or Zinc. Bronzes can be further broken down into four families for both wrought and cast alloys. Bronze Families The wrought bronze alloy families are: · Copper-Tin-Phosphorus alloys (Phosphor Bronzes) · Copper-Tin-Lead-Phosphorus alloys (Leaded Phosphor Bronzes) · Copper-Aluminium alloys (Aluminium Bronzes) · Copper-Silicon alloys (Silicon Bronzes) The cast bronze alloy families are: · Copper-Tin alloys (Tin Bronzes) · Copper-Tin-Lead alloys (Leaded and high leaded Tin Bronzes) · Copper-Tin-Nickel alloys (nickel-tin bronzes) · Copper-Aluminium alloys (Aluminium Bronzes) Other Alloy Groups Copper-Nickel Alloys As the name suggests, the principal alloying element is Nickel. They can contain other alloying elements or simply have Nickel alone. Copper-Nickel-Zinc Alloys These alloys are commonly known as “Nickel Silvers” due to the colour of the alloy. They contain Zinc and Nickel as the principal alloying elements and may also contain other alloying elements. Leaded Coppers Leaded Coppers are cast Copper alloys with 20% or more Lead added. They may also contain a small amount of Silver but have no Tin or Zinc. Special Alloys When alloys have chemical compositions that do not fall into any of the other categories mentioned, they are grouped together as “special alloys”. Free Machining Coppers Free machining properties are imparted upon Copper alloys by the addition of Sulphur and Tellurium. Recycling Copper alloys are highly suited to recycling. Around 40% of the annual consumption of Copper alloys is derived from recycled Copper materials.

Background

Brasses are alloys of copper and zinc (generally 5 to 40%), and may contain small amounts of other alloying elements. Most are available in a range of forms and can be fabricated by casting, forging, stamping, rolling, extrusion and machining.

They fall into two classes, the alpha alloys with less than 37% zinc which are ductile and can be cold worked and the alpha/beta or duplex alloys which are harder and stronger with limited cold ductility.

Lead can be added as an alloying element resulting in a brass that can be rapidly machined and produces minimal tool wear. Additions of aluminium, iron and manganese to brass improve strength, whilst silicon additions improve wear resistance.
Key Properties

· High ductility (alpha alloys)

· Can be hot worked

· Hardness and brittleness increase with increasing beta alloy formation (i.e as zinc content increases above 37% zinc)

· Aesthetically pleasing colour
Applications
High Pressure Gas Valves

High pressure gas valves are commonly made from high tensile brass containing small additions of aluminium, iron or manganese.
Plumbing Systems

Dezincification resistant brass is used for fittings in valves, connectors and taps in pump and plumbing systems. This particular alloy contains a small addition of arsenic and is specially heat treated so that the composition is homogeneous as water in some countries will attack zinc rich areas of the metal.
Marine Applications

Additions of tin or aluminium to either alpha or duplex brasses improves corrosion resistance in sea and brackish waters for applications such as propellers.
Gilding Metals

Brass containing 10 to 20% zinc has a very similar colour to gold. Hence, this composition is often used for costume jewellery and architectural applications.
Other Applications

Heat exchangers, springs, car radiators, fasteners, hot formed parts, extruded sections, forgings, condenser tubes, architectural, sections, pressure tubing, bearings, bushes, ornamental features, gearwheels.

Background

Since the 1930’s and 1940’s many methods have been used for making electrically conductive interconnects on insulating substrates. The often conflicting requirements of cost, electrical insulation, thermal management, track definition, track adhesion, signal transfer speed, current-carrying capability, resistance to adverse working environments, physical strength, performance at high frequencies and so on, have meant that varying degrees of success have been achieved. However, during the last few years the process of copper-plating ceramic has been greatly improved. It can now be considered as a serious alternative to well-established interconnect methods such as etched Cu/epoxide-glass laminates, ‘screen-and-fire’ thick-film circuits, evaporated-metal-on-glass thin-film circuits and etched thick-film.
Copper-Plated Ceramics

Copper-plated ceramic addresses the interconnection requirements of many of the latest electronics systems. The key features stem from the combination of the insulator, the conductor and the manufacturing methods.
Materials and Sizes

The normal insulator used is 96% alumina ceramic. When the highest performance at frequencies above 5GHz is required, 99.5% alumina is used, but since the prices differ by a factor of ten, it is used only when applications require lower losses at higher frequencies. Individual circuits can be produced in any size up to the dimensions of the ceramic panel used, usually 100mm x 100mm or 150mm x 100mm. If more than one circuit fits on to the panel, they are usually made in multiples, with each circuit printed onto prescribed section.
Why Use Alumina for the Insulator?

The electrical properties of alumina are excellent. The insulation resistance is very high and, over the range that affects circuit boards, does not change significantly with either temperature or humidity. The thermal conductivity is reasonable, being a little under one tenth that of copper but around one hundred times that of most organic materials.
Why Use Copper for the Conductor?

The conductor is pure electroplated copper. For all practical purposes only silver has higher electrical conductivity, but copper is cheaper, much more metallurgically stable and its solderability, regarding tin-lead solders, is very well understood. Conductor thickness can range between 5μm and 100μm with only a minimal additional cost for higher thickness. At the highest thickness some loss of resolution capability occurs - the ultimate resolution is mainly limited by the surface quality of the substrate. The conductors have near rectangular cross-sections, very low surface area to volume ratio and the top surface of the conductor is as smooth as that of the substrate. The electrical resistance of the tracking is about 1 milliohm per square for a thickness of 25μm
Other Materials

Despite the fact that pure copper is eminently suitable for solder assembly, it is often necessary to add other materials for various reasons, such as:

· Preventing oxidation during storage, aesthetics, wirebonding and protection against solder-bridging and physical damage

· Organic anti-tarnish coatings prevent oxidation and discolouration by sulphur-containing gases. Plated gold (sometimes over plated nickel) is used both for aesthetics and where wire-bonding is contemplated

· Tin-lead can give retention of solderability during longer storage periods

· Photo-imaged solder mask minimises solder‑bridges and physical/handling damage

· Electroless silver is also available.

These finishes may cover the entire circuit or can be applied only in selected areas.
Performance of Copper-Plated Ceramic Circuits

Concerning the reliability of copper-plated ceramic circuits, a number of tests similar to those carried out on thick film circuits have been made and, in general, the overall performance has been found to be equivalent or superior to conventional thick film. Adhesion of conductors is excellent and, when using a nail head pull test, it is normal for either the wire or ceramic to break, even after ageing at 150°C.

When assessing reliability it is important to relate the test to the technology. For example, the specification for a biased damp-heat test needs to take account of the fact that the electric field between two tracks 50μm apart is much higher than for two tracks 250μm apart for the same applied voltage.

Table 1. Comparison of various circuit technologies.

	Plated copper	Thick Film Ag/Pd	Thick Film Au	Co-Fired Ceramic
Track resolution	50	250	150	150
Track resistivity	1-2	10-30	2-4	5-10
Solderability	Outstanding	Good	N/a	Very Goog
Wire-bonding Au	Yes	?	Yes	Yes
Wire-bonding Al	Yes	Yes	Not pure gold	Yes
Unit costs	Low	Low	High	Low
Tooling costs	Low	Low	Low	High

Economics of Materials Selection

If the needs of the particular application can be met by standard processing of FR-2 or FR-4 laminates, it is unlikely that the benefits of copper-plated ceramic will justify the higher cost. However, if the use of other types of expensive base-board materials such as PTFE-glass or glass-silicone is being contemplated, then it is probable that a very cost-effective solution can be found by choosing copper-plated ceramic.

When compared with single-layer silver thick-film circuitry, copper-plated ceramic gives a broadly similar cost. However, if more than one layer is required in thick film or if gold-based conductors are required, then copper-plated ceramic will almost certainly be cost-effective.
Features and Advantages of Copper-Plated Ceramic Circuits

Features, advantages and benefits can be summarised as follows:

· Higher circuit density than conventional FR-2, FR-4, PTFE, polyimide, thick-film and co-fired ceramic circuits

· Outstanding high-frequency characteristics

· Excellent thermal management and heat-transfer performance

· Outstanding solderability and wire-bonding assembly characteristics

· Low tooling costs and quick turnaround of prototypes.
System Design

A key step in the design of many electronics systems is to divide the system into sub-modules which can be independently assembled and tested. A major benefit of the `modular' approach is that the best available assembly technique can be used for each module, which can then, together with others, be comparatively easily assembled on to relatively simple boards, exactly the right combination for minimising costs and optimising performance.
Interconnects for Modules

Several possible techniques are available for interconnecting such modules, for example, high-density plated copper is useful in a number of applications. It is more versatile than the so-called ‘silicon hybrid’ but cannot achieve the interconnect density afforded by this thin-film method.

The costs per unit area associated with copper-plated ceramic are believed to be lower than for ‘silicon hybrid’, particularly as plated-ceramic may not need additional packaging and the track-resistance is lower.
Where Copper-Plated Ceramics Have Advantages

Situations in which copper-plated ceramic is advantageous include:

· Where the module requires both ‘chip-and-wire’ and solder assembly, particularly when ceramic chip-carriers and chip-capacitors are involved. Selective-plating of the copper gives excellent wire-bonding characteristics and the combination of bulk-metal and substrates with good thermal conductivity leads to outstanding solderability. The ability to make 50μm-wide tracks allows wire-bond sites to be placed close to semiconductor devices, which is a key benefit when comparisons are being made with thick film and co-fired ceramic

· When TAB (tape-automated bonding) is contemplated. The copper tracks are finished with plated tin-lead, enabling multi-lead connections as fine as 100μm track and gap to be soldered without the formation of solder balls or solder bridges

· Where additional packaging is not wanted. It is quite possible to use the assembly with just the attachment of a lead-frame (and maybe plastic encapsulation for the wire-bonded devices)

· If film (printed) resistors are required but in combination with one or more of the other benefits mentioned.

The technology enables patterned conductors to be added to both sides and also to the edges of substrates. Solder bumps have also been added to substrates by the selective plating of tin-lead. Bumps as small as 50μm on a 100μm pitch suitable for flip-chip bonding have been produced.

Background

The Copper/aluminium binary alloy displays shape memory characteristics but has a transformation temperature that is generally considered too high for practical use. The addition of nickel to this system has resulted in another family of shape memory alloys (SMA’s), the CuAlNi alloys with transformation temperatures in the range 80 to 200°C.

CuZnAl alloys also exhibit shape memory capabilities, but are less common than the CuAlNi alloys.
Advantages of CuAlNi SMA’s

CuAlNi SMA’s are popular due to their wide range of useful transformation temperatures and small hysteresis. They are also the only SMA’s that can be used at temperatures over 100°C.

Compared to Ni-Ti SMA’s, the CuAlNi alloys are much cheaper to make as they use cheaper raw materials and do not require sophisticated processing as do the NiTi alloys.
Composition and Transformation Temperature

CuAlNi SMA’s usually contain 11-14.5% aluminium and 3-5% nickel, with the balance being copper. The aluminium content strongly influences the alloys’ transformation temperature.

Reducing the aluminium content below 12% can also improve the alloys’ mechanical properties. Adding manganese (approximately 2%) can reduce the transformation temperature, while the addition of small quantities (approximately 1%) of boron, cerium, cobalt, iron, titanium, vanadium and zirconium are also commonly added to control grain size. However, additions should be made carefully as they can upset the stability of the structure.

The alloy Cu13Al14Ni is a commonly used commercial grade from this family of alloys.
Production

The most common method of producing these alloys is induction melting. Powder metallurgy processes can also be used to produce fine grained structures without the need to grain size control additives.

Hot working is the only satisfactory fabrication method. CuAlNi alloys can be hot worked in air.

Following hot working, they are subject to a suitable solution heat treatment involving controlled cooling (often water quenching), which will help to dictate properties such as transformation temperature.

Postquench ageing is often required to establish the transformation temperature, as the as-quenched transformation temperature is usually unstable. This process is normally carried out above the Af.
Thermal Stability

Thermal stability of copper-based SMA’s is limited by decomposition kinetics and hence, prolonged exposure to temperatures above 200°C should be avoided. Similarly, ageing at lower temperatures can also have an effect on the transformation temperature, e.g. ageing in the martensitic state will tend to stabilise this phase.
Key Properties

· Density 7.10-7.15 g/cm3

· Values for Young’s modulus and yield strength are higher for the high temperature phase of the alloy.

· Recoverable strain is approximately 4-5%.
Applications

· Actuators

The following table contains chemical compositions of drawn wire, rod, bar and strip aluminium alloys

Alloy	Si		Fe	Cu		Mn		Mg		Cr		Zn		Ti	Other7		Al
	min	max	Max	min	max	min	max	min	max	min	max	min	max	max	min	max	min
12001	Si+Fe 1.0 max			-	0.05	-	0.05	-	-	-	-	-	0.10	0.05	0.05	0.15	99.06
2100	-	0.40	0.7	5.0	6.0	-	-	-	-	-	-	-	0.30	-	0.054	0.15	rem
32031	-	0.60	0.7	-	0.05	1.0	0.5	-	-	-*	-	-	0.10	-	0.05	0.15	Rem
5056	-	0.30	0.40	-	0.10	0.05	0.20	4.5	5.6	0.05	0.20	-	0.10	-	0.05	0.15	Rem
5251	-	0.40	0.50	-	0.15	0.10	0.50	1.7	2.4	-	0.15	-	0.15	0.15	0.05	0.15	Rem
6061	0.40	0.80	0.70	0.15	0.40	-	0.15	0.8	1.2	0.04	0.35	-	0.25	0.15	0.05	0.15	Rem
6063	0.20	0.60	0.35	-	0.10	-	0.10	0.45	0.9	-	0.10	-	0.10	0.10	0.05	0.15	Rem
6201A2	0.50	0.70	0.350	-	0.04	-	-	0.6	0.9	-	-	-	-	-	0.05	0.15	Rem
62533	-	-	0.50	-	0.10	-	-	1.0	1.5	0.04	0.35	1.6	2.4	-	0.05	0.15	Rem
6262	0.40	0.80	0.70	0.15	0.40	-	0.15	0.8	1.2	0.04	0.14	-	0.25	0.15	0.055	0.15	Rem
7075	-	0.40	0.50	1.2	2.0	-	0.30	2.1	2.9	0.18	0.28	5.1	6.1	0.20	0.05	0.15	rem

Note:

1. 0,0008% max beryllium for welding electrode and filler wire only

2. Boron 0.06% max

3. Silicon 45 to 65% max of actual magnesium content

4. Lead, bismuth 0.20% min to 0.60% max each

5. Lead, bismuth 0.40% min to 0.70% max each

6. The aluminium content for unalloyed aluminium not made by a refining process is the difference between 100.00% and the sum of all other metallic elements present in amounts of 0.010% or more each, expressed to the second decimal place before determining the sum.

7. Analysis is regularly required only for elements for which specific limits are shown, except for unalloyed aluminium. If however, the presence of other elements is suspected, or indicated in the course of routine analysis, further analysis is required to determine that these elements are not present in excess of the amount specified.