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Oxygen-Free Copper

Luvata oxygen-free copper OF-OK® and its silver bearing derivatives were developed in co-operation with motor and generator manufacturers to meet their specific needs.

Among the industrial copper grades, oxygen-free copper provides the highest electrical and thermal conductivity and therefore, the lowest losses in electrical devices. OF-OK passes the hydrogen embrittlement test (ASTM B577, ISO2626) and, unlike oxygen bearing grades, can be joined by welding, brazing or soldering. OF-OK has excellent cold working characteristics which allows us to design and manufacture sophisticated components from it.

OF-OK® Oxygen-Free Copper

OF-OK is a high-purity copper with electrical conductivity of at least 100 % IACS. The maximum oxygen content is 10 ppm (0.001%) and the copper is resistant to hydrogen embrittlement.

Manufacturing OF-OK

OF-OK manufacturing starts with high-quality copper cathodes melted under strictly controlled conditions and cast in an inert atmosphere into cakes. During this process the copper is not allowed to come into contact with air. Intermediate or final annealing is done either in a reducing atmosphere or a vacuum.


The most important properties of Luvata OF-OK copper are its purity and freedom from oxygen. It also has high electrical and thermal conductivity, toughness, good working qualities and high surface quality.

The purity of OF-OK (Cu min 99.99%) gives it high electrical conductivity, but its main advantages are its immunity to hydrogen embrittlement and the fact that it can be flow formed better than any other copper grade. High purity and homogeneity ensure the consistency of its material properties. Consistency from the first to the last piece, and from batch to batch, reduce setting time and machine down time.


OF-OK copper is the ideal material for:

  • Electrical and electronic applications
  • Printed circuit boards
  • Heat sinks for semiconductor bases

Welding and Brazing

Hydrogen embrittlement occurs when hydrogen ions diffuse into copper at high temperatures, and form water with the oxygen atoms they find there.  This water vapour has a high enough pressure to make pores in the copper.

Hydrogen embrittlement can also occur when copper components are brazed or welded in a reducing atmosphere containing hydrogen. In commercial copper grades, which usually contain 200 to 600 ppm (0.02 - 0.06%) of oxygen, the result is a completely brittle metal. In OF-OK we guarantee the oxygen content will be a maximum of 10 ppm (0.001%). The lack of oxygen and the low impurity content mean that OF-OK copper is well-suited to all types of welding and brazing.

Silver Bearing Copper OF-OK (Ag)

Alloying copper with silver significantly improves e.g. its softening resistance properties. Even a small amount of silver enhances the softening temperature of Luvata OF-OK without sacrificing its high conductivity and formability. Typical applications for silver bearing copper are commutators for small motors and graphic plates for the engraving industry.

OFE-OK® Certified Grade

High-purity, certified grade copper has a minimum electrical conductivity as high as 101.0% IACS, making it ideal for demanding electronic applications. Its impurity content is less than 40 ppm (0.0040%), with no single impurity exceeding 25 ppm (0.0025%). The content of volatile elements in vacuum at high temperatures Cd, Hg and Zn is a maximum of 1 ppm. To ensure high resistance to hydrogen embrittlement, the maximum oxygen content is restricted to 5 ppm (0.0005%).

Properties of Certified Grade OFE-OK Copper

  • High purity
  • Highest possible electrical and thermal conductivity
  • Excellent formability and impact strength
  • Excellent weldability, brazability and solderability
  • Excellent for high-vacuum applications
  • Immune to hydrogen embrittlement
  • Very adherent oxide scale
  • High homogeneity and reliability

Manufacturing OFE-OK

Certified Grade OFE-OK follows a different manufacturing, control and inspection process from regular grade OF-OK®. Only specially selected cathode copper is used, and ingots are produced in the middle of the operating period – when conditions are most stable.

Well-suited to Electronic and Other Demanding Applications

The low content of highly volatile elements such as P, Pb, S, Zn, Cd, Hg results in low volatility under high vacuum and makes certified grade OFE-OK well-suited to the electronics and laser optic industries, and vacuum technology applications. It is readily joined by brazing or welding and is the optimum grade of copper for electron beam welding.

The electronics industry uses glass-to-copper seals, which require an adherent oxide film on the surface. This film may be rendered non-adherent if traces of phosphorous, (which is commonly used as an oxidant) are present. To prevent this, OFE-OK contains less than 3 ppm (0.0003%) of phosphorous. Certified grade copper meets or exceeds the requirement of Class 2 of ASTM F68 ‘Oxygen Free Copper in Wrought Forms for Electron Devices’.

At cryogenic temperatures the electrical and thermal properties of OFE-OK are superior to any other copper grade. OFE-OK can be supplied with a guaranteed minimum RRR (Residual Resistance Ratio) value of 400.


OF-OK copper is the ideal material for:

  • Printed circuit boards
  • Electrical and electronic conductors
  • Bonding applications
  • Magnetrons
  • Vacuum interrupters and tubes

Quality control

Luvata has 100% microscopic inspection throughout the manufacturing process guarantees that each piece of the material has metallographic contamination complying with either Class 1 or Class 2 of ASTM F68-77 and F68-82. A full inspection according to ASTM B170 is made for each cut piece after casting, for each product after hot rolling and on the final product.

A quench test for oxide adherence is made to ensure that the material is suitable for glass-to-metal seals. Every OFE-OK certified copper carries a test certificate, which is a guarantee that impurities in the material are held below the specified limits and that the electrical conductivity is at least 101.0% IACS and the material is oxygen-free.


Oxygen-Free Copper for Industrial Applications
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See also our many alloy data sheets in the Document Library

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