Copper Assembly: Electrical, Thermal, and Brazed Joining

A bolted copper bus connection lives or dies by contact resistance. Copper oxidizes in air, and copper oxide is a poor conductor, so a joint that is merely tight but oxidized runs hot under current and degrades over time. Good electrical assembly cleans the mating faces to bright metal, often with an abrasive pad or a deoxidizing joint compound, immediately before assembly. Clamp load matters as much as cleanliness. The joint needs enough pressure to break through residual oxide and maximize the real metal-to-metal contact area, but copper is soft (C110 is around 40 HRB) and creeps under sustained load, so the joint relaxes over time and resistance climbs. Assemblers counter this with Belleville washers that maintain clamp force as the copper creeps, and they specify controlled torque rather than gut-feel tightening. Finish choice affects long-term performance. Tin or silver plating on bus bars resists oxidation and keeps contact resistance stable for decades, which is why switchgear and power-distribution copper is usually plated rather than bare. Silver plating is preferred for high-temperature and high-reliability connections despite its cost.

Copper's high thermal conductivity makes it the material of choice for heat exchangers, cold plates, and RF and microwave hardware, and those assemblies are usually brazed or soldered rather than bolted. Copper brazes beautifully: copper-phosphorus (BCuP) filler is self-fluxing on copper and produces strong, leak-tight joints in heat-exchanger and refrigeration assembly without separate flux. The high conductivity that makes copper useful also makes it hard to braze, because heat conducts away from the joint as fast as you put it in. Assemblers preheat large copper parts and use higher torch output or furnace brazing to bring the whole joint to temperature uniformly. Furnace and vacuum brazing are standard for multi-joint assemblies like cold plates and waveguide, giving clean, oxide-free, repeatable joints. Soldering handles lower-temperature and electronic copper joints, from plumbing to PCB and connector work. The same conductivity challenge applies, plus oxidation control via flux. For oxygen-free C101 used in vacuum and RF assemblies, brazing and welding avoid the hydrogen embrittlement that plagues ordinary tough-pitch copper, which is exactly why C101 exists.

The three grades sourced here serve different masters. C110 (ETP, electrolytic tough pitch) is the everyday electrical copper, roughly 100 percent IACS conductivity, used for bus bars, grounding, and general electrical assembly. It is cheap and conductive but contains residual oxygen, which makes it prone to hydrogen embrittlement if brazed or welded in a reducing atmosphere. C101 (OFHC, oxygen-free high-conductivity) removes that oxygen, giving slightly better conductivity and, critically, immunity to hydrogen embrittlement. That makes C101 the grade for assemblies that will be brazed, welded, or used in vacuum and high-temperature service, including particle-accelerator and semiconductor hardware, RF components, and vacuum chambers. Tellurium copper (C145) addresses copper's one big assembly weakness: pure copper machines terribly, smearing and gumming up tools. Adding tellurium gives free-machining behavior (machinability around 85 percent of free-cutting brass) while keeping roughly 90 percent IACS conductivity. It is the grade for assemblies needing many machined copper parts, threaded copper components, connectors, and electrode bodies, where pure copper would be impractical to machine in volume.

Copper is relatively noble, so in mixed-metal assemblies it tends to drive corrosion in aluminum and steel neighbors rather than corroding itself. A copper lug bolted to an aluminum bus or terminal is a classic galvanic and bimetallic-joint problem: aluminum corrodes, and the differing thermal expansion plus aluminum creep loosens the joint. Assemblers use bimetallic transition washers, plated transition pieces, and joint compounds to manage copper-to-aluminum connections, which are extremely common in power distribution. Cost-wise, copper is a commodity that tracks the metals market and runs well above aluminum and steel per pound, and its density makes copper parts heavy. Designers minimize copper mass, use plating to protect cheaper substrates, and reserve solid copper for where conductivity genuinely demands it, often substituting aluminum bus with larger cross-section where weight and cost favor it. Lead time for copper assembly is usually driven by plating and brazing operations rather than the copper itself, since bar and plate stock is readily available. Tin and silver plating, furnace brazing, and leak testing on sealed assemblies are the typical schedule drivers.