1. Composition Requirements for High-Conductivity Copper
High-conductivity copper generally refers to copper with an electrical conductivity of no less than 100% IACS (International Annealed Copper Standard). To meet this requirement, strict control of chemical composition is essential.
First, the base copper purity must be sufficiently high. For standard high-conductivity copper, the mass fraction of copper should be at least 99.90%. For high-precision electronic and electrical applications, the purity is often higher than 99.95% or even reaches 99.99%. Higher copper purity reduces electron scattering caused by impurities and lattice defects, thus improving conductivity.
Second, the content of harmful impurity elements must be strictly limited. Common impurities such as phosphorus, iron, sulfur, oxygen, lead, bismuth, antimony, arsenic, and nickel significantly reduce electrical conductivity.
Typical composition limits for high-conductivity copper include:
Phosphorus ≤ 0.005%
Iron ≤ 0.005%
Sulfur ≤ 0.005%
Oxygen ≤ 0.02% (for oxygen-bearing copper) or lower for oxygen-free copper
Total non-copper impurities ≤ 0.05%–0.10%
Oxygen-free copper (OFC) further controls oxygen below 0.001% to avoid brittleness and conductivity loss during high-temperature processing.
2. Is Higher Copper Content Always Better?
In pure copper, higher copper content does improve electrical and thermal conductivity, but it is not always better for all applications.
Within a certain range, increasing copper purity reduces impurity scattering and significantly improves conductivity. However, excessively high purity brings problems:
Cost increases sharply as ultra-high purification requires complex processes such as electrolytic refining and vacuum melting.
Mechanical strength decreases because pure copper is very soft and has low hardness and wear resistance.
In some cases, trace beneficial elements (such as small amounts of silver or cadmium in controlled concentrations) can improve strength and softening resistance without seriously damaging conductivity.
Therefore, copper purity should be selected according to actual needs. For example, common electrical components use 99.90%–99.95% purity, while high-frequency signals and ultra-precision devices require 99.99% or higher.
3. Effects of Impurity Elements on Conductivity
Almost all impurity elements in solid solution or precipitation form reduce the electrical conductivity of pure copper.
Soluble impurities (phosphorus, iron, nickel, arsenic, antimony, bismuth) distort the copper lattice and strongly scatter electrons, leading to a sharp drop in conductivity. Even 0.01% phosphorus can cause obvious conductivity loss.
Insoluble or weakly soluble impurities (lead, sulfur) form second-phase particles at grain boundaries, increasing electron scattering and also reducing conductivity.
Oxygen forms Cu₂O particles, which affect both conductivity and processing performance. Oxygen-free copper is used in special applications to avoid these effects.
In general, the smaller the atomic radius difference and solubility difference between impurity and copper, the smaller the damage to conductivity; otherwise, the impact is more serious. For high-conductivity applications, minimizing impurity content is the most effective way to ensure performance.
