Copper-based Conductivity Materials

Heat treatable copper-iron alloys have a higher strength than copper whilst maintaining a reasonably high electrical and thermal conductivity and excellent welding, soldering and brazing properties.

History

This precipitation-hardenable alloy was developed by Olin Brass in the USA in 1964 (C19400). It offered a combination of high conductivity and strength and proved an excellent alternative to copper and brass for electronic and electrical applications such as lead frames and connectors.

In Europe the alloy is designated CW107C and appears in PD6641:1999 and as a leadframe alloy in EN1758:1998. There is no British standard for this alloy.

Heat Treatment

The precipitation heat treatment involves heating the copper-iron alloy to 800 to 900oC and water quenching. This is called solution treatment and the alloy is in its softest condition. Subsequent precipitation (age) hardening at lower temperatures of 425 to 500oC results in the formation of finely dispensed iron precipitates in the alpha matrix; these are responsible for the increased strength and hardness.

The copper-iron alloy may be stress relieved at 200-300oC.

Properties

The alloy has the following combination of properties:

  • Tensile strength: 370-580 N/mm2
  • Proof strength: 110-485 N/mm2
  • % Elongation: 10-1
  • Hardness (HV): 80-170
  • Electrical conductivity: 60-65% IACS
  • Thermal conductivity: 260-265 W/moC

Fabrication

 Process Rating
 Cold formability
Excellent
 Hot formability
Fair
 Soldering Excellent
 Brazing Excellent
 Oxyacetylene welding
Not recommended
 Gas shield arc welding
Excellent
 Resistance welding
Not recommended

Machining

This is rated at 20-25% which is satisfactory. Free-machining brass is 100%.

Resistance to Corrosion

Copper-iron has good resistance to corrosion in industrial and marine atmospheres. It is insensitive to stress corrosion cracking. However, it is susceptible to attack in the presence of ammonia, sulphur, hydrogen sulphide and mercury.

Stress Relaxation

This is decrease in stress under constant strain, typically observed in steel bolts in turbine casings at high temperature which must be regularly tightened.

For copper alloys used in electrical contacts, it is important to maintain good contact force throughout the functional life of the product and have good stress relaxation resistance.

One indication of stress relaxation may be obtained by measuring the % of stress which is retained as a function of temperature and time. Results on copper iron strip test pieces tested after 1000 hours are:

Temperature oC

% Retained Applied Stress

100

70-90

150

50-75

200

30-60


It is clear that the % retained stress decreases as the temperature increases; results such as this will be one factor used in the design of high performance components from copper-iron strip, such as clips, contacts, connectors, switches, pins and lead frames which operate in this temperature range of 100-200
oC.

Strength at Temperature

Lead frames may be subject to temperatures as high as 350oC for a few minutes; tests have shown that copper-iron shows very little loss of strength after 100 minutes at 350oC.

Applications

Copper-iron has a combination of strength and weldability making it ideal for the following applications.

  • Circuit breaker components
  • Contact springs
  • Electrical connectors
  • Electrical springs
  • Clamps
  • Plug contacts
  • Fuse clips
  • Switches
  • Sockets
  • Cable wrap
  • Lead frames
  • Pin grid array (PGA) in semi-conductor industry

Available Forms

Copper-iron is available as strip, tube and wire.

Specifications

Below are the specifications for Europe, US and Asia. Note that for USA and Asia, some compositions are not identical. For equivalent standards from other countries visit the Copper Key website.

Europe: CW107C (CuFe2P) (European Standard EN designation).

USA: C19400 (American Society for Testing and Materials ASTM designation).

Japan: C1940 (Japanese Industrial Standards, JIS designation).

Further information on copper-iron, and other conductivity materials, is available at the Copper Alloys Knowledge Base.

Application Example 1: Lead Frames

Lead frames connect the wiring from electrical terminals on the semi-conductor surface to the large scale circuitry on electrical devices and circuit boards.

Copper-iron, with its combination strength, electrical and thermal conductivity, formability, plateability, corrosion resistance and the ability to withstand temperatures up to 350oC for a short time without softening, is an ideal choice for this application.

Application Example 2: Pin Grid Array

A pin grid array, often abbreviated PGA, is a type of integrated circuit packaging. In a PGA, the package is square or rectangular, and the pins are arranged in a regular array on the underside of the package. The pins are commonly spaced 2.54 mm apart, and may or may not cover the entire underside of the package.

There is a strong demand for materials of high thermal conductivity to dissipate the heat produced in the operation of the PGA, as well as high electrical conductivity. An ideal material for this application is CW107C in wire form, which is widely used as PGA lead pins for personal computers, and tin plated square wires have been adopted in connector terminals for automobiles.

The high electrical conductivity 65% IACS, high thermal conductivity 260 W/m oC and high tensile strength of up to 580 N/mm2 are the reasons why CW107C wire is used for pin grid arrays in application such as a microprocessor.

Quick Facts

Properties

The alloy has the following combination of properties:
  • Tensile strength: 370-580 N/mm2
  • Proof strength: 110-485 N/mm2
  • % Elongation: 10-1
  • Hardness (HV): 80-170
  • Electrical conductivity: 60-65% IACS
  • Thermal conductivity: 260-265 W/moC

Applications

  • Circuit breaker components
  • Contact springs
  • Electrical connectors
  • Electrical springs
  • Clamps
  • Plug contacts
  • Fuse clips
  • Switches
  • Sockets
  • Cable wrap
  • Lead frames
  • Pin grid array (PGA) in semi-conductor industry

Available Forms

  • Strip
  • Tube
  • Wire

Application Example 1: Lead Frames

Lead frame. (Courtesy of Wieland Werke.)
Lead frame (Courtesy of Wieland Werke).

Application Example 2: Pin Grid Array

Pin grid array in a microprocessor. (Wikipedia.)
Pin grid array in a microprocessor (Wikipedia).
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