Two Designations from Two Systems
C101 and C106 are frequently compared because both are called plain copper, yet they are not two grades from the same table. C101 is the short form of UNS C10100, the oxygen-free electronic grade. C106 is a legacy British Standard designation for phosphorus-deoxidised copper, which in the UNS system corresponds to C12200, the high-residual-phosphorus grade commonly known as DHP copper, and to the related low-phosphorus C12000.
The practical consequence is that the two materials are specified for entirely different reasons, and a purchase order that simply says C101 or C106 without naming the designation system can easily deliver the wrong metal.
Composition and Conductivity
| Property | UNS C10100 oxygen-free electronic | C106 phosphorus-deoxidised, UNS C12200 |
|---|---|---|
| Copper content | 99.99 % min | 99.90 % min |
| Oxygen content | 0.0005 % max | Not applicable, fully deoxidised |
| Phosphorus | Not deliberately added | 0.015-0.040 % |
| Electrical conductivity | 101 % IACS min | Approximately 85 % IACS |
| Thermal conductivity at 20 °C | Approximately 390 W/(m·K) | Approximately 339 W/(m·K) |
| European designation | Cu-OFE, CW009A | Cu-DHP, CW024A |
| Typical product forms | Strip, bar, wire, busbar for electronics | Tube, sheet, plate for water and process duty |
Note that the European designation of C10100 is Cu-OFE, written CW009A. The similar-looking CW004A refers to electrolytic tough pitch copper, which is a different grade and a common source of confusion in equivalency tables.
What Phosphorus Does to the Material
Phosphorus is added to C106 as a deoxidiser. It combines with the oxygen dissolved in the melt and removes it, so the cast material contains no cuprous oxide particles and is not susceptible to hydrogen embrittlement when it is heated in a reducing atmosphere during brazing, welding or annealing. This is the single most important practical difference between the two grades.
Joining. C106 is easier to braze and to weld because there is no oxygen present to react with the reducing gases in the flame or furnace atmosphere. C10100, being essentially oxygen free, is also safe in reducing atmospheres, but its very high purity makes it more difficult to machine and gives it a softer, gummier cutting behaviour.
Conductivity. The residual phosphorus in C106 remains in solid solution and scatters conduction electrons, which is why its conductivity is around 85 % IACS instead of the 101 % IACS of C10100.
Machinability. C10100 offers better machinability than might be expected from its purity because there are no oxide inclusions, but free-cutting brasses remain far easier to machine than either grade.
Choosing Between Them
C10100 is selected where conductivity is the governing requirement: vacuum and electronic components, waveguide and RF enclosures, high-power busbar and switchgear, magnet windings, anodes for vacuum devices, and any part in which residual phosphorus would degrade performance or contamination control. The grade is normally ordered in strip, bar or wire form under ASTM B152 or ASTM B187 with the applicable temper.
C106 copper is selected where the material will be joined, formed or exposed to water and where optimum conductivity is not needed. Domestic and commercial water tube, refrigeration and air-conditioning tube, roofing and architectural sheet, heat-exchanger tube and general engineering plate are all normal applications. It is specified through standards such as ASTM B88 for water tube, ASTM B75 for seamless tube, ASTM B42 and ASTM B111 for heat-exchanger and condenser duty, and the equivalent European tube standards.
Inspection, Temper and Traceability
Both grades are ordered by temper, and the temper designation should always be quoted with the material code, because a soft annealed strip and a hard rolled strip of the same analysis behave quite differently in forming. ASTM B601 provides the temper designations used across the copper family. Composition is verified spectrographically, conductivity is checked against the IACS requirement, and tube and strip products are normally supplied with eddy-current or ultrasonic inspection, dimensional verification and a mill certificate that records the heat number, chemical analysis and mechanical results.
When comparing quotations, the safest practice is to ask for the UNS number, the equivalent standard designation and the temper on the certificate. A supplier who quotes only a short code such as C101 or C106 is not giving enough information to confirm that the correct material has been supplied.
FAQ
Q: What is the main difference between C101 and C106 copper?
C10100 is oxygen-free electronic copper with at least 99.99 % copper, no deliberate phosphorus and around 101 % IACS conductivity. C106 is phosphorus-deoxidised copper, equivalent to UNS C12200, with 0.015-0.040 % phosphorus, at least 99.90 % copper and around 85 % IACS conductivity.
Q: Is C106 the same as C12200?
Yes in practice. C106 is the former British Standard designation and C12200 is the UNS designation for the same phosphorus-deoxidised, high-residual-phosphorus copper, widely written as DHP or Cu-DHP.
Q: Why is C10100 conductivity higher?
Because it contains no residual phosphorus. Elements in solid solution scatter conduction electrons, so the phosphorus that protects C106 during joining costs it roughly 15 percentage points of IACS conductivity.
Q: Which grade is easier to braze and weld?
C106, because the phosphorus has already removed the oxygen from the melt. The absence of cuprous oxide means the material cannot be embrittled by hydrogen in a reducing flame or furnace atmosphere.
Q: Is C101 copper oxygen free?
Yes. C10100 is specified with a maximum oxygen content of 0.0005 %, which is why it is classed as oxygen-free electronic copper and why its properties approach those of elemental copper.
Q: Which grade should be used for water tube?
C106, the phosphorus-deoxidised grade, since it brazes reliably and provides ample conductivity for plumbing, refrigeration and heat-exchanger duty. C10100 is reserved for electrical, electronic and vacuum applications where the conductivity difference is decisive.
