Why Conductivity and Precision Pull in Different Directions
Electrical conductivity in copper is degraded by anything that disturbs the regularity of the lattice. Alloying elements, dissolved impurities and second-phase particles all scatter electrons, so the highest conductivity always belongs to the purest metal. Precision manufacturing, on the other hand, rewards strength and dimensional stability, and those properties normally come from alloying or cold work. C10200 sits deliberately at the purity end of that spectrum, which is exactly why it dominates conductor applications and why it presents specific processing challenges.
The grade is essentially unalloyed copper: copper content is 99.95% minimum, oxygen is limited to 0.001% maximum, and total impurities other than copper and silver are capped at 0.05%. That composition is defined in ASTM B152 for flat rolled products and appears under the corresponding designations CW008A in EN 1412, C1020 in JIS and TU2 in GB/T 5231.
Core Properties for Conductor Duty
| Property | Value | Engineering significance |
|---|---|---|
| Electrical conductivity | 100% IACS minimum (58 MS/m) | Meets the international annealed copper standard |
| Electrical resistivity | 1.724 micro-ohm-cm at 20 C | Basis for busbar and cable sizing calculations |
| Temperature coefficient of resistance | 0.00393 per C | Used to correct resistance at service temperature |
| Thermal conductivity | about 390 W/(m K) | Removes joule heat from current-carrying parts |
| Density | 8.94 g/cm³ | Weight penalty in busbar and winding design |
| Elastic modulus | 117 GPa | Governs spring-back in forming and contact force |
| Annealed tensile strength | typically 200-250 MPa | Low strength is the central manufacturing constraint |
Applications in Electrical Conductors
In power transmission and distribution, C10200 busbars, flexible connectors and winding strip carry current with minimal resistive loss, and the low loss translates directly into reduced temperature rise inside switchgear cabinets. In electronics it appears as high-frequency coaxial inner conductors, terminal stock, relay parts, contacts and lead frames, where its stability under repeated thermal cycling keeps contact resistance predictable.
Electric vehicle and renewable energy hardware has become a major outlet. Battery module interconnects, motor hairpin conductors, charging connectors and inverter busbars all rely on the combination of high conductivity and high ductility that only a very pure copper can deliver, since the parts must be formed into tight radii without cracking.
The Precision Manufacturing Challenge
Three effects dominate when C10200 is machined or formed to tight tolerance.
Low strength and hardness. Annealed C10200 deforms readily, so clamping forces, feed rates and stack handling can all introduce burrs, dents or edge damage on thin strip and small terminals.
Surface oxidation. Freshly machined or annealed copper reacts with air to form a thin oxide film. That film raises contact resistance and interferes with soldering and plating, so parts are usually protected by tinned or bright finishes, by controlled-atmosphere packaging, or by process-time limits between operations.
Thermal growth. Copper expands noticeably with temperature. In fine-pitch punching, laser cutting and diamond turning, heat generated at the cutting edge changes the effective dimension of the workpiece, so temperature control and light finishing passes are essential.
Controls That Keep Both Requirements Met
Selection of temper is the first lever. Soft O60 or O61 material suits deep drawing and bending, while H02 and H04 tempers provide the yield strength needed for spring contacts and connector bodies without losing much conductivity. Where conductivity is not the absolute priority, dilute silver-bearing copper offers improved softening resistance at elevated temperature while staying close to the C10200 conductivity band.
On the shop floor, the practical controls are sharp tooling with positive rake geometry, generous coolant to remove heat, light finishing cuts, and handling systems that avoid metal-to-metal contact. For cleanliness, parts are degreased, lightly pickled and then protected before storage. Inspection typically combines conductivity measurement, tensile or hardness testing and dimensional checks with optical or eddy current examination of the surface.
FAQ
Q: Why does C10200 reach 100% IACS while alloys stay lower?
Conductivity depends on lattice purity. With 99.95% minimum copper and no intentional alloying additions, electron scattering is minimised, so C10200 reaches the international annealed copper standard value.
Q: Is low strength a defect of C10200?
It is a design trade-off rather than a defect. Purity buys conductivity; when greater strength is required, a harder temper or a dilute alloy must be selected instead.
Q: How should oxidation be controlled during production?
By finishing operations in a protective atmosphere where possible, by keeping the interval between machining and plating short, and by applying a tinned or anti-tarnish finish on stock that will be stored.
Q: Which temper is used for electrical connectors?
H02 half-hard is common for terminals and contact parts, while softer tempers are used where severe forming precedes assembly.
Q: Does cold work reduce conductivity?
Cold work reduces conductivity only slightly compared with alloying, which is why heavily formed C10200 parts still meet their electrical requirement.
Q: How is conductivity measured on finished parts?
Normally by eddy current conductivity meters on the finished part, supported by four-point resistance measurement per ASTM B193 on coupons.
