Copper Stamping: Alloy Grades for Busbars, Terminals & Lead Frames

Copper stamping is a conductivity-versus-strength trade from the opening material decision. Nearly every stamped copper component on a high-speed line comes from one of three grades, and picking the wrong one shows up as a field failure, not a paperwork issue: a busbar that runs too hot at rated current, or a contact that relaxes its spring force after ten thousand cycles. The capability range we run - strip from 0.05 to 3.0 mm on 45-110 ton presses at up to 300 strokes per minute with ±0.005 mm positioning - is identical across all three grades; what changes is the alloy's electrical, mechanical and thermal personality.

The three grades - C11000 electrolytic tough pitch copper, C10200 oxygen-free high conductivity copper, and C17200 beryllium copper - sit at three different points on the same trade. C11000 and C10200 carry current at roughly 100-101% IACS and give up strength; aged C17200 delivers tensile strength near 1100-1380 MPa and gives up conductivity, dropping to about 18-25% IACS. Everything downstream - the die design, the plating specification, the tolerance map, the cost model - follows from which of these three points your part actually needs.

The Three Workhorse Grades

Three grades carry nearly every copper stamping job that leaves a progressive die. Each is a deliberate balance of conductivity, strength and cost, and the differences between them are large enough to decide the failure mode of the finished part.

Grade	Common name	Conductivity (% IACS)	Tensile range (MPa)	Typical job
C11000	ETP copper (electrolytic tough pitch)	~100	220-380 by temper	Busbars, high-current terminals, battery interconnects
C10200	OFHC copper (oxygen-free high conductivity)	~101	220-380 by temper	Plated contacts, welding-critical parts, formed flat parts
C17200	Beryllium copper (age-hardened)	~18-25	1100-1380 aged	Spring contacts, relay blades, lead frames

C11000 carries the bulk of current-carrying stampings: at roughly 100% IACS it is the reference grade for busbar and terminal work, where the design question is temperature rise at rated current, not strength. The oxygen content of ETP copper is acceptable for most formed and plated parts, which keeps it the default when no welding or brazing step is involved. C10200 is nearly identical in conductivity but holds oxygen below its specified maximum, which matters for parts that will be welded, brazed or plated in aggressive chemistries - oxygen in the matrix can cause porosity and embrittlement at weld temperature, so welding-critical programs pay a small premium for the oxygen-free grade. C17200 flips the trade completely: age-hardened it reaches 1100-1380 MPa tensile - roughly three to five times the strength of work-hardened C11000 - at the cost of dropping to about one-fifth the conductivity, which is fine for signal contacts carrying milliamps and needing spring force for millions of cycles.

What the table does not show is that these three grades can run through the same progressive die family. The press, the feed and the quality system do not change when the coil changes: we stamp all three on the same high-speed lines, which means the grade decision stays a design decision rather than a supplier constraint. That matters at quoting time, because it means the alloy call can be revisited after the DFM review without changing the production platform.

The Conductivity vs Strength Trade

Conductivity and strength pull in opposite directions in copper, and every grade is a point on that curve. At one end, pure annealed copper conducts at roughly 101% IACS and has the strength of a paperclip; at the other, age-hardened beryllium copper is stronger than most steels and conducts at about a fifth of pure copper. The job of the engineer is to find the point on the curve where the part still works, and the job of the stamper is to hit it repeatably.

Temper is the second axis, and it is the one most drawings forget to lock down. C11000 strip is specified across a range from soft annealed (tensile ~220 MPa, high elongation) to hard-drawn (~380 MPa), and the temper chosen is a forming-versus-stiffness decision: soft for deep forms, hard for parts that must hold shape without a frame. Aged C17200 measures roughly 36-44 HRC, which is why it resists permanent set where softer alloys take a bend and keep it. A drawing that says "copper" without a temper is a drawing that leaves the failure mode to chance - the same part can come out springy or limp depending on what the mill shipped.

The practical consequence is that the trade is not "pure copper or beryllium copper" but a two-dimensional map. A terminal that carries 20 A and never flexes belongs on C11000 in a hard temper. A terminal that carries 2 A and must generate contact force for 10 million cycles belongs on C17200. Between those extremes, plated C10200 and C11000 cover a large middle band, and the tie-breaker is usually cost: beryllium copper costs several times more per kilogram than ETP copper, so the spring grade is specified only where the design cannot be fixed another way - thicker section, a forming rib, or a redesign of the contact geometry.

[Data Anchor: Across the three grades, conductivity spans ~101% IACS (C10200) down to ~18-25% IACS (aged C17200), while tensile spans ~220 MPa annealed C11000 up to ~1380 MPa aged C17200. The selection axis is always current capacity versus spring performance, with temper as the fine adjustment.]

Thermal Limits That Drive Field Reliability

Conductivity is not the whole thermal story; every grade has a temperature ceiling that decides where it can live. For C11000 and C10200, softening begins around 250-400 °C depending on temper and time, and continuous service above roughly 200 °C starts to erode the work-hardened strength that stamping relies on. That is why busbar programs specify the grade, the temper and the plating together - a tin-plated C11000 busbar sees reflow temperatures near 190-260 °C during assembly, and the temper and coating must be chosen so the part survives that window without losing its formed shape.

C17200 is a different animal. It is supplied soft and age-hardened to full strength, and its spring properties hold to roughly 200 °C, which is what makes it the standard for relay blades and contacts in engine compartments and industrial controls. Above that ceiling, or after prolonged exposure, stress relaxation erodes contact force quietly - no visible deformation, just contact resistance that climbs until the circuit misbehaves. The general rule for stamped copper of any grade: if the application temperature approaches the softening or relaxation threshold, either move down in conductivity to a stronger grade or redesign the section to carry the load.

Ampacity follows the same table. Design guidance for bare copper bus in still air runs roughly 1-4 A/mm² of cross-section depending on ambient and acceptable temperature rise, and plated or enclosed busbars derate further. At the same section, C11000 carries nearly the full conductor rating while C17200 carries about a fifth - which is why nobody builds a main busbar from spring alloy, and why the alloy decision happens before the current-carrying cross-section is dimensioned.

For parts that sit near a heat source - an engine bay, a battery pack, a lighting driver - the thermal callout on the drawing is as important as the conductivity callout. A contact that passes a room-temperature bench test can fail six months later in a warm enclosure, because relaxation is a time-temperature phenomenon, not a pass-fail one. When the operating temperature is known, the relaxation behavior of the candidate grade should be checked before tooling, not after field returns.

[Data Anchor: Service ceilings: C11000/C10200 continuous service ~200 °C with softening from ~250 °C; C17200 holds spring properties to ~200 °C. Ampacity guidance 1-4 A/mm² for bare copper bus in still air; solder and plating reflow windows (190-260 °C) must be checked against temper retention before the part is designed, not after.]

How Copper Behaves in the Die

Copper's forming behavior is what makes it a joy and a discipline in a progressive die. It work-hardens predictably, which lets a designer raise strength by drafting harder tempers rather than changing alloy - the same C11000 strip can serve a soft, deep-formed part and a hard, springy one. But that same work hardening drives springback: a copper bend wants to return partway to its original angle, and the form tooling must carry compensation angles tuned during tryout, or the final part sits off the drawing. Tighter corners and higher tempers mean more springback, which is why the ±0.005 mm positioning accuracy of the press is half the equation - the die geometry carries the other half.

Copper also galls. It adheres to tool steel under high sliding pressure, so lubrication, clearances and polish matter more than with SPCC steel of the same thickness. Burr control follows the same discipline: clearance between punch and die of roughly 4-8% of strip thickness keeps the burr small and predictable on 0.05-3.0 mm strip, and burr direction is specified on the drawing for parts that must sit flush in an assembly. Because copper conducts, the die also sees electrical considerations in plating - most terminal and contact programs run reel-to-reel selective plating after stamping, so gold, silver, tin or nickel lands exactly where the drawing calls for it, and the strip layout leaves access for the plating fingers.

Die wear deserves its own budget line. Copper is abrasive enough that a high-volume terminal die sees measurable edge wear, and the tool room schedule - wire EDM, CNC and grinding in-house - decides whether sharpening happens on a plan or after scrap appears. The maintenance interval is a number that belongs in the quote: how many hits between sharpening, how many sharpening cycles before insert replacement, and what that adds to the per-part price. A well-maintained copper die routinely outlives the program it was built for, while a neglected one drifts tolerance and starts producing burr at the least convenient moment.

[Data Anchor: Die-side rules: punch-to-die clearance ~4-8% of strip thickness for burr control; springback compensation tuned in tryout per temper; selective reel-to-reel plating applied post-stamp so precious metal cost stays on the contact zone alone.]

Plating and Surface Finish

Nearly every stamped copper part that matters electrically is plated somewhere. The copper provides the bulk conductivity; the plating provides the contact surface, the solderability, or the corrosion resistance. The two decisions - grade and finish - are made together, because the plating chemistry and thickness depend on what the copper has to do in service.

Our plating lines run selective reel-to-reel gold, silver, tin and nickel at 2-8 µm, with zinc at 5-12 µm, and salt-spray performance is verified to ASTM B117. Selective plating matters for cost: it puts the precious metal only on the contact zone, so a terminal that needs a gold contact surface does not pay to gold-plate the whole strip. The strip layout has to anticipate the plating fingers - where the reel dips, how the carrier web holds the part, and how the selective pattern lands on the finished geometry.

Plating	Typical thickness	What it buys	Where it is used
Tin	2-8 µm	Solderability, low cost, good for power contacts	Terminals, busbars, battery interconnects
Silver	2-8 µm	Low contact resistance, high conductivity surface	High-current contacts, switchgear, EV busbars
Gold (with nickel underplate)	2-8 µm	Oxidation-free contact surface, stable signal contact	Signal terminals, connectors, lead frames
Nickel	2-8 µm	Diffusion barrier, wear resistance, corrosion	Underplating, high-temperature parts
Zinc	5-12 µm	Sacrificial corrosion protection	Structural copper parts, outdoor hardware

The order of operations matters. Plating after stamping keeps the precious metal off the shear edge and off the die; plating before stamping is chosen when the coating must survive the forming without cracking. Pre-plated strip changes the die conversation - the coating can flake at the bend, so the bend radius and lubrication plan must be adjusted. When the contact resistance budget is tight, the plated surface finish and the base alloy flatness are controlled together: a coining station flattens the contact pad, and the plating lands on a surface that was made flat by the die, not by luck.

Corrosion performance is a system property, not a coating property. A nickel-under-gold stack on C10200 behaves differently from the same stack on C11000 because the base metal oxygen content changes what happens at the interface over years of service. For parts that must survive salt spray or humidity, the grade, the plating and the test specification should be named on the drawing together - the test is only meaningful when the material system it validates is the material system that ships.

Matching the Grade to the Product

Application is where the trade resolves. For stamped busbars and bent busbars, C11000 in a medium-to-hard temper is the workhorse: full conductivity for the current path, enough strength to hold the formed shape, and strip utilization of 60-80% on a progressive layout that nests several bends in one pass. For terminals and contacts that must carry current and survive cycling, C10200 or C11000 with selective plating covers the vast majority of programs. For anything that must generate its own contact force - relay blades, spring contacts, and the fine fingers of a lead frame - C17200 is the grade that holds force over millions of cycles, because no amount of geometry compensates for an alloy that relaxes at operating temperature.

Product family	Recommended grade	Typical plating	Why
Busbars, battery interconnects	C11000, hard or half-hard temper	Tin or silver 2-8 µm	Full conductivity; plating protects the joint surface
Power terminals	C11000 or C10200	Tin or silver 2-8 µm	Current-carrying with formed geometry
Welding-critical parts	C10200	Per application	Low oxygen avoids weld porosity
Signal contacts, spring beams	C17200	Gold with nickel underplate 2-8 µm	Contact force over millions of cycles
Lead frames (fine fingers)	C17200 or C19400 family	Selective gold or silver	Strength, flatness, thermal stability

EV battery programs push the busbar side of this harder than any other market: stamped C11000 busbars and bent busbars carry pack current between cells and modules in programs running hundreds of thousands of parts per year, with the same strip-utilization discipline (60-80%) and reel-to-reel plating applied before or after forming depending on the surface requirement. The tolerance map travels with the part: ±0.005 mm features on the terminal pads, flatness controlled by coining where the busbar stacks against cells. The EV busbar stamping guide covers the sizing and material logic in more depth; the alloy call underneath both is the one made here.

Lead frames deserve a special note because they combine every constraint at once. Fine fingers need spring force or at least rigidity, the frame must stay flat through plating and molding, and the thermal cycle of soldering must not relax the geometry. C17200 is the standard answer where the fingers must hold position, and the flatness is held by coining stations rather than by hoping the strip arrives flat. For higher-volume commodity frames, the C19400 copper-iron family offers a cheaper middle ground with good strength and thermal conductivity - another reminder that the grade map is wider than three points, and the DFM review should check whether a middle alloy fits before defaulting to the expensive end.

The selection order is fixed: define the current and the allowed temperature rise, then the required force and cycle count, then the assembly heat exposure, then the plating. Each constraint eliminates grades in sequence, and what remains is usually one defensible choice. That ordering is what a DFM review checks before anything else, and it is why the same copper strip, the same die, and the same press can produce parts as different as a 300 A busbar and a signal contact - the alloy decision comes before the die design.

Cost and Sourcing Decisions

The alloy choice is also a cost decision, and it compounds through the whole quote. Strip material is the first layer: ETP copper is the cheapest of the three, OFHC carries a small premium for the oxygen control, and beryllium copper costs several times more per kilogram. But raw material is only the first layer. The second layer is utilization - what percentage of the coil becomes parts. On a progressive layout, 60-80% utilization is the working range, and the strip layout is designed before any cutting happens. A layout that nests bends across several parts in one pass turns scrap into product; a layout that does not leaves the buyer paying for every gram of skeleton.

Temper availability shapes the schedule as much as the price. Hard-temper strip is ordered to the final strength, and a program that changes temper mid-stream changes the mill order, the springback compensation in the die, and the tryout cycle. Freezing the temper at RFQ stage is cheaper than revising it after tooling. The same applies to the plating: a selective plating pattern is designed into the strip layout, and changing the pattern after the die is cut means new access geometry, not just a new chemistry.

The volume economics decide which grade is even affordable. Beryllium copper makes sense on a spring contact that ships a million pieces; it is a harder sell on a structural bracket that could be redesigned in brass. When volume is low, the honest recommendation is often rapid prototyping or pre-production runs to validate the design before the die commitment, then conversion to progressive tooling when volume data justifies it. When volume is high, the die amortization collapses and the conversation moves entirely to per-part price - which is where strip utilization and plating pattern do the heavy lifting. The high-volume stamping guide covers the production-system side of that calculation.

Copper is also a volatile commodity, and the quote should say what the material basis is. A fixed-price quote absorbs the metal price; a floating quote passes it through. Neither is wrong, but the buyer should know which one they signed, because a copper swing of tens of percent over a program life is bigger than most piece-price negotiations. Ask for the material index and the date of the basis, and check that the quote's scrap credit - the buyback of the skeleton - is a real line, not a rounding error.

A Selection Checklist for Your Drawing

Run the selection in the same order every time, and the grade stops being a guess. The checklist below is the one a DFM review applies to a copper part before anything is quoted.

• Define the current and the allowed temperature rise. If the part carries real amps, the cross-section and the grade must pass the temperature budget. Pure copper leads unless formability forces a compromise.
• Define the force and the cycle count. If the part must flex and hold force, C17200 is the default and the relaxation curve is the deciding number. If it never flexes, hard-temper C11000 or C10200 covers the job.
• Check the assembly heat exposure. Reflow, soldering and potting temperatures must be checked against the temper retention and the relaxation threshold of the chosen grade.
• Choose the plating with the grade. Tin for solder, nickel-under-gold for signal, silver for high current. Name the thickness band and the test standard (ASTM B117 for salt spray) on the drawing.
• Lock the temper and the tolerance map. Temper on the material callout, ±0.005 mm features named for the critical locations, flatness controlled by coining where the part stacks.
• Run the cost model. Material cost, utilization, scrap credit, plating pattern and tooling amortization in one table. If the total does not make sense at your volume, the grade or the layout is wrong.

The same discipline applies to the wider copper family. Brass and phosphor bronze cover parts that sit between pure copper and beryllium copper on the same axes of strength, fatigue, relaxation and cost. For spring contacts specifically, the spring contact design guide walks the beam geometry that the alloy has to survive.

Send Us Your Drawing

The cost of guessing the grade wrong is measured in field failures - a busbar that runs hot at rated current, or a contact that relaxes after ten thousand cycles. Conductivity, tensile range and thermal ceiling pick the grade; the drawing and application data pick everything else. When the application data is complete - current, temperature, cycle count, assembly heat, plating requirement - the grade decision is usually one defensible choice, and the die design follows it.

Send us your drawing for a grade-matched DFM review within one business day. Include the current, the operating temperature and the cycle life, and we will return the grade, the temper and the plating stack that hits the spec without paying for headroom you do not need.