Copper Sheet Metal: Conductivity, Softness, and the Forming Trade-offs

Copper sheet grades are differentiated mainly by purity and oxygen content, which in turn set conductivity and weldability. C110 (ETP, electrolytic tough pitch) is the most common and least expensive, about 99.9 percent copper with a small amount of oxygen present as copper oxide, and it carries roughly 100 percent IACS conductivity. It is the default for busbars, grounding, and electrical connections where cost matters and the part is not brazed or welded in a hydrogen atmosphere. C101 (OFE, oxygen-free electronic) removes that oxygen, which buys two things: slightly better conductivity and, more importantly, immunity to hydrogen embrittlement during brazing and welding. That makes C101 the choice for vacuum components, semiconductor hardware, and any part that will see high-temperature joining in reducing atmospheres, where the oxygen in C110 would react with hydrogen and cause internal cracking. The grade decision usually comes down to whether the part will be brazed or fired in hydrogen; if yes, pay for C101, if no, C110 is the economical pick.

Pure copper is gummy and miserable to machine, smearing and building up on tool edges, so when a sheet part needs significant drilling, tapping, or milled features, tellurium copper (C145) earns its place. Adding about 0.5 percent tellurium transforms machinability to roughly 85 percent of free-machining brass while retaining around 90 to 95 percent IACS conductivity, a small conductivity sacrifice for an enormous gain in machinability. In sheet metal terms this matters when a copper part is not just cut and bent but needs precise machined holes, threads, or features integrated with the flat work. Tellurium copper costs more than C110 and is less common in thin sheet, so the trade is real, but for a busbar or contact block with tapped holes and tight features, it saves so much machining grief that it is usually worth specifying. If the part is purely laser-cut and bent with no machining, the premium is wasted and C110 is the better value.

Copper in the annealed (soft) temper forms beautifully, taking tight bends and deep draws without cracking, which is why it is loved for radiators, gaskets, and formed electrical parts. But annealed copper is structurally weak and dents easily, so for parts that must hold shape under load, half-hard or hard tempers give more rigidity at the cost of formability and more springback. Copper also work-hardens as it forms, so heavily worked parts may need intermediate annealing to restore ductility. The honest framing for buyers is that copper is a functional material, not a structural one. If a part needs to bear meaningful mechanical load, copper is the wrong choice and a copper-clad or plated steel, or a copper conductor mounted on a steel bracket, is the right architecture. Specify copper for what it does uniquely, carry current and heat, and let a stronger metal carry the loads, rather than fighting copper's softness with thicker gauge that wastes expensive metal.

Copper's great fabrication advantage is how easily it joins. It solders and brazes readily, which is the standard way to assemble copper electrical and thermal parts, and resistance and TIG welding are possible though copper's high thermal conductivity means a lot of heat is needed because it conducts away from the joint so fast. For C110, remember the hydrogen-embrittlement caveat on high-temperature joining; use C101 where that applies. Bare copper oxidizes quickly, going dull brown and eventually green, which is cosmetic in many applications but matters for contact resistance on electrical surfaces. Tin plating is the common protection for connectors and busbars, preserving solderability and low contact resistance, while nickel plating is used as a barrier layer and for harsher environments. Where the natural copper look is wanted, clear lacquer slows oxidation. The takeaway is that an electrical copper part usually carries a plating spec, and that finish step should be priced and scheduled, since it batches at an outside plater and adds a few days of lead time.