Grounding Clips and Cans: Stamped EMI and RF Contacts
Short answer: a stamped grounding clip is a spring contact whose only job is to make a reliable, low-resistance electrical connection between two metal parts — usually a shield can and a PCB ground pad, or two chassis pieces. The number that decides whether it works is contact force: production grounding fingers typically press with 0.3–1.5 N (30–150 gf) through a deflection of 0.2–0.8 mm, which holds contact resistance below roughly 10–50 mΩ and survives 10,000+ compression cycles. Materials are beryllium copper, phosphor bronze or spring-temper stainless, plated in tin, nickel or gold. Stamping makes them at $0.005–$0.05 each.
Every electronic product you have opened has grounding clips somewhere: the spring fingers along a shield can's edge, the clip that grounds a metal lid to a board, the contact that ties an antenna or connector shell to chassis ground. They are stamped from thin strip, formed into shape on a progressive die, and rely entirely on spring force to keep the connection alive across temperature swings, vibration and thousands of assembly cycles. Because they look trivial, they are usually the last thing reviewed and the first thing that fails an EMI test or an ESD event. This guide covers the numbers that matter.
What Grounding Clips and Cans Actually Do
A grounding can or clip has two jobs. The first is electrical: provide a low-impedance path between the item being grounded and the ground plane, and do it without solder — the clip's spring force is the connection. The second is mechanical: keep that force over the product's life, through thermal cycling, shock and repeated assembly. When a designer says "the shield isn't grounding properly," the failure is almost always a contact that lost its force, an oxidation film on the surface, or a plating that wore through.
Grounding cans — the fence-and-lid shields soldered around ICs — also need their lids grounded to the frame. Stamped fingers on the lid, or dimples in the frame, press against the mating surface and complete the shield's perimeter electrically. An ungrounded lid turns the shield into a slot antenna; a lid with good stamped grounding contacts every few millimetres keeps the shield's effectiveness where the design intended. The deeper shielding story is in our EMI shielding contacts guide, which covers finger geometry in detail.
Normal Force: The Number That Decides Performance
Contact resistance between two clean metal surfaces drops as force rises, because more microscopic asperities touch. But force is not free: higher force means stiffer material, more stress, and sooner or later permanent set when the clip is deflected. The designer's job is to pick the smallest force that reliably breaks through surface films and holds resistance, then prove the clip still delivers it at end of life.
| Application | Typical normal force | Working deflection | Cycles expected |
|---|---|---|---|
| PCB ground clip (board to chassis/shield) | 0.5–2.0 N | 0.2–0.6 mm | 10,000+ |
| Shield can lid finger | 0.3–1.0 N | 0.2–0.5 mm | 1,000–10,000 |
| Connector shell / I/O grounding clip | 1.0–3.0 N | 0.3–0.8 mm | 5,000–20,000 |
| Battery / module grounding contact | 0.5–2.0 N | 0.3–1.0 mm | 1,000–10,000 |
Why so much force for such a small part? Because plating is not a perfect conductor film: tin forms oxides, nickel passivates, and even gold needs pressure to guarantee metal-to-metal contact through dust and handling residue. A clip pressing with 0.3 N or less is a reliability lottery. Design rule of thumb: pick a material and thickness so the clip delivers its required force at maximum deflection with stress below about 60–70% of the yield strength, then verify with samples — springback and real stress are not reliably predictable from hand calculations on parts this small.
One more number belongs on the specification: the current the clip may have to carry. Most grounding clips only steer static and ESD, but some pass real current — antenna feeds, bonding straps, chassis returns — and then conductivity and cross-section matter, not just force. Tell the supplier the worst-case current and its duration; it changes the alloy and thickness choices even when the mechanical drawing is identical.
Materials: Spring Alloys, Not Structural Steel
Grounding clips are springs first and conductors second. The material must survive bending into shape, deliver force without taking a permanent set, and carry enough conductivity for the grounding function. That narrows the list to a few copper alloys and spring-temper stainless.
| Alloy | Conductivity (% IACS) | Max use temp | Spring quality | Relative cost |
|---|---|---|---|---|
| Beryllium copper C172 | 22–28% | 200°C+ | Excellent, low set | 4–7× |
| Phosphor bronze C5210 | 13–15% | 150°C | Very good | 1.5–2× |
| Brass C260 (hard) | 28% | 100°C | Fair, set at low stress | 1.0× (baseline) |
| Stainless 301 (full hard) | 2–3% | 250°C+ | Very good | 1.5–2× |
| Nickel silver | 5–8% | 150°C | Good | 1.8–2.5× |
Beryllium copper is the classic grounding-clip alloy because it combines spring strength with real conductivity and resists relaxation at temperature; its cost and handling restrictions are why phosphor bronze and 301 stainless take the jobs where conductivity is secondary. Steel clips are fine for grounding force if the resistance budget allows — skin effect at RF means a steel contact can ground a shield adequately when the connection is short. Whatever the alloy, order it to a specified temper: soft strip forms easily but delivers no force, and over-hard strip cracks in the die. Plating choice is covered in our stamped contact plating guide; for grounding, tin over a nickel barrier is the workhorse, gold flash appears where corrosion and low resistance both matter, and bare beryllium copper is used where the alloy's own surface is acceptable.
Why Stamping Is the Only Serious Process
Grounding clips are high-volume, thin, springy shapes with tight form tolerances — a textbook progressive-die product. Strip feeds through stations that blank, form, coin and sometimes plate or separate in-die at 200–600 strokes per minute with multiple parts per stroke, delivering clips that cost $0.005–$0.05 and never need a human hand to be identical. No other process comes close at volume: machining a 0.1 mm spring finger is absurdly slow, and wire EDM or laser cutting cannot match stamping's edge quality and speed for millions of pieces.
| Route | Tooling cost (indicative) | Part cost at 1M/yr | Notes |
|---|---|---|---|
| Progressive die stamping | $4,000–$15,000 | $0.005–$0.05 | The standard; best edge quality |
| Photo etching | $500–$2,000 | $0.05–$0.30 | Prototypes, no burr, slower |
| Wire EDM / laser | $0–$500 setup | $0.50–$5.00 | Samples and micro runs only |
The stamping tolerance story matters here because a grounding clip's force is a function of its formed geometry: ±0.05 mm on a 2 mm-long finger changes force by a noticeable margin, which is why we hold formed features tightly and check force on sample lots rather than assuming the drawing is enough. If the contact also has to carry signal, the material and plating guidance in our metal shrapnel and spring contact guide applies directly.
Designing a Grounding Clip That Passes on the First Try
Start from the force you need and the space you have, then choose thickness: a clip's force scales roughly with the cube of thickness and linearly with width, so thickness is the fastest lever but also the fastest way to overstress. Keep the working deflection inside the elastic range with margin — 30–70% of the available travel is a sane window for most finger designs. Radius every bend at least one material thickness; sharp bends on spring temper are crack starters. Think about how the part is held: grounding clips are usually press-fit into a PCB hole or a slot, so the retention features (barbs, dimples) are part of the same die, and they need their own force budget.
Plating direction matters too: if the strip is pre-plated, forming happens after plating and sharp bends can crack the finish exactly where the contact wipes. Specify which surfaces are functional, what the wipe length is, and whether the contact should slide (wipe) or press (butt) against the mating surface. A wipe of 0.2–0.5 mm cleans oxides and gives a much more reliable connection than a pure butt contact. Then send the drawing to a die shop that runs stamped terminals and contacts daily — the DFM feedback on a grounding clip is worth more than the die itself.
Verification is cheap relative to the failure it prevents. We measure clip force on a force gauge against a test anvil at the specified deflection, check contact resistance with a micro-ohmmeter through the plated interface, and cycle sample lots to the expected lifetime before production tooling is cut. Those three numbers — force at working deflection, resistance through the joint, and force after cycling — catch more grounding failures than any drawing dimension. If your product has to pass EMC or ESD testing, validate the clip in the real assembly early: the difference between a passing and a failing shield is often a clip whose force looked fine on paper and was not.
Frequently Asked Questions
Q: How much contact force does a grounding clip need?
A: Production grounding clips typically press with 0.3–1.5 N through 0.2–0.8 mm of deflection. Below about 0.3 N the connection becomes unreliable because surface films and plating oxides are no longer broken through reliably.
Q: What is the best material for a stamped grounding clip?
A: Beryllium copper C172 gives the best combination of spring force and conductivity but costs 4–7× brass. Phosphor bronze C5210 and full-hard 301 stainless cover most jobs; brass is cheapest but takes permanent set under sustained deflection.
Q: How many cycles does a stamped grounding clip survive?
A: Well-designed clips on beryllium copper or phosphor bronze survive 10,000+ compression cycles, and shield-lid fingers 1,000–10,000 cycles. Fatigue life collapses if working stress stays near yield, so design force with stress margin, not at the limit.
Q: Can a steel grounding clip work for RF grounding?
A: Yes. At RF, skin depth in steel is only a few micrometres, so a short steel contact can ground a shield adequately when force, plating and wipe are right. Copper alloys only become necessary when the contact must also carry signal current.
Q: What tolerances can you hold on stamped grounding clips?
A: Formed features such as finger height and bend angles typically hold ±0.05 mm on our progressive dies, with blanked outline at ±0.02–0.05 mm. Because contact force depends on formed geometry, we verify force on first articles and sample lots.
Related Resources
- EMI shielding contacts guide — finger geometry, contact force and materials for shields and grounding.
- Stamped terminals and contacts — the grounding clips, fingers and contact springs BQUQ stamps on progressive dies.
- About BQUQ — ISO9001-certified source factory in Dongguan running stamping, CNC, springs and heat sinks under one roof.
- Contact us — send the drawing and receive a stamped-part quote within 12 working hours.
Authored by the BQUQ Engineering Team. BQUQ is an ISO9001-certified source factory in Dongguan, China, running CNC machining, metal stamping, custom springs, heat sink and collet lines under one roof. Send drawings to sc@bquq.com or WhatsApp +86 13713157787 for a quote within 12 working hours. www.bquq.com
