Copper Alloy Stamped Parts: Grades, Plating and When to Use Each

Wrong copper alloy choice is the quietest way to kill a stamped component. We see it every year on connector and lead-frame programs: a buyer specs "copper" because it sounds conductive, the supplier ships brass to hit a price, and the finished terminal passes incoming inspection at room temperature. Six months into field service the contact resistance drifts, the spring loses clamp force, or the plating blisters at the bend. By then the die is paid for, the reel is in the customer's line, and the failure traces back to one decision made on a spreadsheet. Pick the wrong alloy and you trade a few cents per part for field returns, requalification, and a credibility hit that no supplier discount covers. Pick right and the part runs for the life of the device with margin to spare.

Why the grade decides everything before the die is cut

Stamping locks in the material first. You cannot recover conductivity you never had, and you cannot add fatigue strength by plating over a soft substrate. The five copper families we run on precision parts - pure copper, brass, phosphor bronze, beryllium copper, and copper-nickel white copper - sit at completely different points on the conductivity-versus-strength curve. A C11000 terminal carries current almost like the copper busbar in your wall. A C5191 spring carries almost none of it but holds its shape under 100,000 cycles. Treat them as one "copper" and you will mis-specify half your bill of materials.

The three numbers that settle most arguments are conductivity (%IACS), tensile strength (MPa), and stress-relaxation resistance. Conductivity is what your electrical engineer cares about. Strength and relaxation are what your mechanical engineer cares about. A good stamped-part spec balances all three against formability - because if the material cracks in the die, none of the other numbers matter.

Grade-by-grade: what the data actually says

C11000 / C10200 - pure copper

This is the electrical workhorse. C11000 (ETP, electrolytic tough pitch) and C10200 (OF, oxygen-free) both run about 100-101% IACS conductivity - that is the reference copper against which every other alloy is measured. C10200 drops the oxygen to under 10 ppm, which matters when you are welding or brazing lead frames where porosity at the joint is not acceptable. Tensile strength lands around 210 MPa annealed and climbs to roughly 380 MPa in hard temper. Density is 8.89 g/cm³.

Use it where current carrying is the job: busbars, ground straps, power terminals, battery tabs, and thick lead frames that need to move amps, not hold a spring. The trade-off is softness and poor springback - pure copper will not hold a cantilever contact. It also work-hardens fast, so deep or repeated draws need intermediate anneals. For stamped power parts where conductivity is non-negotiable, this is the default, and C10200 is the call when the downstream process is fusion welding.

C2600 / C2680 - brass

Brass is copper with zinc, and the zinc cuts conductivity hard in exchange for formability and cost. C2600 (70/30 cartridge brass) and C2680 (65/35 yellow brass) both sit near 28% IACS conductivity. Tensile strength runs about 300 MPa annealed and reaches 550-580 MPa in spring-hard temper. The drawability is excellent - brass is the material we reach for when the part has a deep shell, a tight radius, or a complex progressive-die form that would split in pure copper.

Use brass for non-current-critical structural stampings: shields, brackets, connector shells, and housings where the metal is mechanical, not electrical. It also takes tin plating cleanly and costs well below the bronzes. The limit is conductivity and a moderate relaxation rate, so we keep brass out of anything that must carry signal current or hold a precise contact force over years of heat cycling.

C5191 / C5210 - phosphor bronze

Phosphor bronze is where spring performance lives. C5191 (about 5% tin) and C5210 (about 8% tin) run low on conductivity - roughly 12-13% IACS - but deliver tensile strength of 550-650 MPa in spring temper with outstanding fatigue life. Tin and a trace of phosphorus give it corrosion resistance and a stable modulus that brass cannot match. C5210, the higher-tin grade, pushes strength and wear resistance further at a small cost to formability.

This is the contact-spring material: the little cantilever and coil springs inside connectors, relay blades, and switch contacts. When the part must flex millions of times and still hold clamp force, phosphor bronze is the safe, proven choice. The penalty is that 13% IACS means it is a poor conductor - you design the current path through a separate contact area or a thicker cross-section, not through the spring itself. We plate the contact tips (gold or silver) and let the bronze do the mechanical work.

C17200 - beryllium copper

Beryllium copper is the premium spring alloy and the only one here that combines real strength with useful conductivity. C17200 comes solution-treated at about 22% IACS and, after precipitation hardening, reaches tensile strength of 1,100-1,380 MPa while keeping that 22% IACS ballpark. Fatigue strength and stress-relaxation resistance are the best of the copper family by a wide margin. It is also non-sparking and dimensionally stable through heat treat, which is why it shows up in oil-and-gas, aerospace, and high-reliability connectors.

Use C17200 where you need a spring that also carries meaningful current, or where relaxation at 125-150 °C would wreck a phosphor-bronze part. The downsides are cost - it runs several times the price of bronze - and beryllium handling controls in the mill and plating line. For most commercial connectors, phosphor bronze does the job cheaper; C17200 earns its price only when the spring must survive high temperature, high cycle count, or a combination of current and force that bronze cannot hold.

White copper / copper-nickel

White copper, the copper-nickel family, trades conductivity for corrosion resistance and a neutral, silvery appearance. A representative grade such as C70600 (90/10 cupronickel) runs about 7-9% IACS conductivity with tensile strength near 275-415 MPa. It does not tarnish like brass, it resists seawater and industrial atmospheres, and it is non-magnetic - useful where that matters. Formability is good, though work-hardening means planned anneals on deep draws.

We reach for white copper on marine, medical, and decorative-precision parts where appearance and corrosion resistance beat conductivity: connector shells in harsh environments, sensor housings, and watch- or instrument-grade trim. It is rarely the electrical path; it is the durable, good-looking envelope around one.

Application map: which alloy goes where

The grade sections above compress into a working map. The table below is the one we actually use at quoting time, and it is the fastest way to catch a mismatch between the drawing and the application.

Alloy family	Typical stamped parts	Why it wins	Watch out for
C11000 / C10200	Busbars, ground straps, power terminals, battery tabs, lead frames	100-101% IACS, the conductivity reference	Soft, no springback, work-hardens fast
C2600 / C2680	Shields, brackets, shells, housings	Deep-draw formability, low cost, clean tin plating	28% IACS, moderate stress relaxation
C5191 / C5210	Contact springs, relay blades, switch contacts	550-650 MPa spring temper, fatigue life	12-13% IACS, current must bypass the spring
C17200	High-temp springs, current-carrying springs, aerospace contacts	1,100-1,380 MPa hardened, best relaxation resistance	Premium cost, beryllium handling controls
C70600 white copper	Marine shells, sensor housings, instrument trim	Corrosion resistance, silvery finish, non-magnetic	7-9% IACS, planned anneals on deep draws

Temper, formability and the bend-radius budget

The grade fixes the alloy; the temper fixes what the die can do to it. The same C5210 strip in annealed condition forms like a sheet of writing paper, and in spring temper it fights the die and springs back. Copper strip is ordered by temper for a reason: the stamping shop does not "make" the temper, it buys it, and the drawing must name it or the die, the plating and the field behavior are all undecided.

Formability and strength move in opposite directions within every grade. Annealed C11000 at 210 MPa bends and draws easily; hard-temper C11000 at 380 MPa needs larger radii and springs back visibly. The same logic runs through the whole family: a spring-hard brass clip that holds 550-580 MPa will crack at the radius an annealed blank takes for granted. The practical rule is to keep the inside bend radius above the material's floor for the ordered temper, put the radius on the drawing, and let the die builder hold it instead of guessing.

Springback is the second half of the formability story. Hard tempers spring back more, so a 90° form on spring-hard bronze lands at 93-95° unless the die overbends or coins the corner. Coining - squeezing the bend zone to lock the angle - is the standard fix, and it adds a little die cost to save a lot of rework. Deep draws have their own budget: pure copper, brass and cupronickel work-harden, so a draw ratio past the annealed limit needs an intermediate anneal or a move to a more drawable temper. When the drawing shows a deep shell in a spring material, that is a conversation to have before tooling, not during first article.

Plating: the second decision that gets ignored

The base alloy gets the part stamped; the plating gets it qualified. Four finishes cover almost everything we plate on copper-alloy stampings, and each earns its place on data, not habit.

Plating	Typical thickness	What it buys you	Where we use it
Tin (Sn)	0.5-3.0 µm, often reflowed	Solderability, oxidation protection, low contact resistance for power	Power terminals, busbar tabs, wire-to-board contacts
Nickel (Ni)	1.0-5.0 µm barrier	Wear and corrosion barrier under precious metal; diffusion stop	Underlayer for gold/silver, EMI gaskets
Silver (Ag)	0.5-2.0 µm	Highest conductivity of any finish, excellent for high-current contacts	High-current connectors, RF contacts, switching
Gold (Au)	0.025-1.0 µm flash to hard gold	Corrosion-free, stable contact resistance, no fretting oxide	Signal contacts, low-level circuits, mating surfaces

Tin is the workhorse for solderable power parts and is usually reflowed to kill the matte whisker-risk. Nickel is almost never the top layer - it is the barrier that keeps zinc or copper from migrating into a thin gold or silver contact and forming a high-resistance intermetallic. Silver wins on conductivity but tarnishes, so it stays on high-current contacts that run warm enough to self-clean. Gold is the signal-contact finish: a thin flash over nickel gives you a contact that reads the same ohm after ten years as on day one. The mistake we correct most often is a thick, expensive gold where a reflowed tin would have passed, or a bare bronze spring shipped with no plating at all.

Plating selection is a cost decision as much as a reliability decision. Gold and silver are precious metals; plating a whole strip to contact thickness when only the mating face needs it is the most common overspend on connector programs. Reel-to-reel selective plating puts gold or silver only on the contact zone, tin only on the solder pad, and leaves the structural shank bare - at a fraction of the full-strip cost and with better thickness control where it matters. On high-volume parts the selective line runs in-line with the press, so the thickness is verified per reel, not trusted to a subcontractor. The full decision framework, including when tin beats gold and when the nickel underplate earns its cost, is in our terminal plating guide.

Plating must survive the forming operation. Plating applied after stamping sees no strain, but pre-plated strip gets bent, and a brittle layer cracks at the radius - a corrosion cell in the making. The rule is to specify the plating sequence (strip-plate then form, or form then plate) on the drawing, because the two routes have different cost structures and different field behavior.

Stress relaxation - the failure mode nobody mentions

Conductivity gets the spotlight; stress relaxation is what actually retires connectors in the field. Stress relaxation is the loss of clamp force at temperature while the spring stays deflected. A phosphor-bronze contact at 85 °C might hold 80-85% of its force after 1,000 hours; push it to 125 °C and that number drops fast, and the contact resistance climbs as the fingers loosen. C17200 holds force far better at the same temperature, which is exactly why it is specified for under-hood and industrial electronics. Pure copper and brass barely count as springs at all - they relax so quickly that we never use them in a deflection-critical role.

The practical rule: if the part is a spring and it lives above 105 °C, run the relaxation curve before you pick the alloy. Do not let a room-temperature tensile number stand in for hot performance. We have seen a "strong enough" brass clip lose half its force in a warm enclosure and let a loosely seated contact arc.

How the alloy moves through the stamping process

The alloy choice also decides how the part runs through the press. High-volume terminals, contacts and lead frames run in progressive dies on high-speed presses, and the material envelope is part of the process design. Strip thickness from 0.05 to 3.0 mm and strip width to 650 mm covers the range from thin bronze contact springs up to heavy pure-copper busbar sections. Presses in the 25-80 ton class run up to 300 strokes per minute with piloted die positioning at ±0.005 mm, which is what makes drawing tolerances on contact geometry repeatable across a full reel.

Spring materials and power materials want different die design. A phosphor-bronze spring needs a die that controls springback and holds the bend radius; a pure-copper busbar needs sharp tooling and tight clearances so the soft material blanks clean instead of dragging a burr. The heavier power parts move to the 45-110 ton press class where the tonnage to blank and coin thick copper is available without distortion. In-house tooling with wire EDM, CNC and grinding keeps the die geometry true, and the quality lab adds CMM, optical measurement and in-line vision to hold the ±0.05 mm class features that connectors live or die on. Our progressive die high speed stamping service page covers the equipment and inspection stack in detail, and the lead frame stamping guide applies the same logic to the thinnest, tightest parts in the family.

Cost economics: the alloy decision is a cost decision

Alloy choice moves piece price through four levers, and understanding them beats negotiating against them. The first is material cost itself: the hierarchy runs beryllium copper well above bronze, bronze above brass, brass above pure copper, with copper's own price volatility on top. The second is utilization. Copper strip is priced by weight and bought in coil; a layout that nests poorly scraps a premium material, while a small outline relaxation on a non-functional edge can move utilization several points at zero functional cost.

The third lever is plating. Selective precious-metal plating instead of full-strip plating can cut the finish cost on a connector program by more than the alloy difference between brass and bronze - which is why the cheapest-looking alloy choice can end up the most expensive system when it forces an upgrade in finish. The fourth is process stability. A spring material that fights the die, springs back unpredictably, or needs extra annealing costs more per good part than a slightly dearer material that runs at full press speed. The piece price that matters is the cost per good part out of the line, not the cost per kilogram of strip.

Tooling amortization closes the picture. The same progressive die spread across 100,000 parts a year carries a fraction of the per-part burden it carries at 10,000, which is why the alloy and plating decisions are locked before the production die is cut. Requalifying a material after tooling - new first article, new plating qualification, new relaxation testing - is a real cost, and it is the strongest argument for getting the alloy right at the quoting stage. Prototype parts from the same tool room that will run volume keep that decision cheap to change early and expensive to change late.

Corrosion, environment and compliance

Copper alloys tarnish, and the tarnish film is a high-resistance layer on a contact. The finishing decision is therefore an environmental decision: tin and gold resist atmospheric corrosion, silver tarnishes but self-cleans on warm high-current contacts, bare bronze grows an oxide that raises contact resistance in low-level circuits. Coastal and industrial atmospheres accelerate everything, which is why salt spray screening per ASTM B117 is a standard gate on marine, automotive and outdoor connector programs.

Galvanic pairing decides what happens at the assembly. Brass and bronze parts mated to aluminum housings or steel hardware form couples that corrode when moisture gets in; a nickel barrier or a plated finish on the stamped part usually closes the gap. Compliance is the paperwork half of the same decision: RoHS restricts lead and other substances in the plating, REACH covers the supply chain registration, and the material certificate must show the actual grade and temper of the coil that ran. None of this is exotic - it is the difference between a part that passes an audit and one that fails one.

Quality gates and material control

The quality system is what makes the alloy choice auditable. Incoming material certification verifies the grade and temper of every coil against the drawing; without it, a "substitution" of brass for bronze is invisible until the field finds it. Temper verification catches a coil that arrived softer or harder than ordered, which changes springback and contact force. Plating thickness is verified on production parts by X-ray fluorescence per batch, and the first article inspection report carries CMM data at the critical contact features.

Factories running IATF 16949:2016 quality systems produce the PPAP-style documentation that connector and automotive programs require, with batch traceability back to the coil and the plating lot. The control plan ties the measurements to the features that matter - contact force, plating thickness, critical dimensions - so a drift shows up in the lab, not in the field. When the paperwork and the parts both trace to one accountable source, the alloy decision is a decision, not a hope.

Supplier evaluation checklist

Five questions separate a copper stamping supplier that will hold the grade from one that will quietly trade it for a price. First, does the quote name the alloy, the temper and the finish, or does it say "copper"? Second, does the shop verify incoming material certificates per coil, including temper? Third, is plating in-house and verified per batch by XRF, or trusted to a subcontractor? Fourth, does the quality system produce first article reports with CMM data and batch traceability under IATF 16949? Fifth, does the DFM review flag formability, springback and relaxation before tooling, or discover them at first article?

Three answers end the conversation early: no temper on the drawing, no incoming certificate control, and no plating verification per batch. Those three gaps are how "copper" becomes brass, and how brass becomes a field return. The connector terminal stamping guide walks the design side of the same decision, and the metal stamping materials guide covers the broader grade landscape across steel, aluminum and copper.

FAQ

What copper alloy should a power terminal use? C11000 or C10200 pure copper at 100-101% IACS when the part must carry current. Choose C10200 oxygen-free when the joint is welded or brazed downstream.

Why is phosphor bronze used for contact springs? C5191 and C5210 deliver 550-650 MPa in spring temper with outstanding fatigue life and a stable modulus, which is what holds clamp force over millions of cycles. The trade is conductivity at 12-13% IACS, so the current path is designed around the spring, not through it.

When does beryllium copper justify its cost? When the spring must carry meaningful current, or survive 125-150 °C service where phosphor bronze relaxes. At 1,100-1,380 MPa hardened, it is the only copper family that combines real strength with useful conductivity.

Why does brass fail as a spring? Brass relaxes too fast at temperature - a clip that seems strong at room temperature can lose half its force in a warm enclosure. Keep brass for structural and shell parts, not deflection-critical contacts.

What plating should a solderable terminal get? Reflowed tin at 0.5-3.0 µm for solderability and oxidation protection. Add a 1.0-5.0 µm nickel barrier under gold or silver when the contact is signal-grade.

Why do copper parts blister or crack at the bend? Either the plating was applied before forming and cracked at the radius, or the bend radius was below the temper's floor. Both are drawing-stage decisions, not field mysteries.

How to pick: a field rule we use

Start with the current. If the part must carry real amps, pure copper (C11000/C10200) leads unless formability forces a compromise, in which case thick brass or silver-plated bronze carries the path. If the part must flex and hold force, phosphor bronze (C5191/C5210) is the default spring and C17200 is the upgrade for heat or cycle count. If the part is mostly structural or a shell, brass (C2600/C2680) or white copper wins on cost, form, or corrosion. Then plate to the contact requirement: tin for solder, nickel-under-gold for signal, silver for high current. Match the alloy to the job and the failure modes listed above largely disappear before the first reel ships.

None of this is theoretical on our floor - we stamp all five families on the same progressive dies and plate them in-house, so the grade and finish are decisions we make with you at the quoting stage, not after a reject. If you are scoping a terminal, connector, lead frame, shield, or small bracket and the alloy call is still open, send us the current, the operating temperature, and the cycle life. We will tell you the grade, the temper, and the plating stack that hits the spec without paying for headroom you do not need - and we will flag it before tooling, not after.

Send us your drawing and requirements for a grade, temper and plating recommendation with a quote.