'Stamped Shield Cans: RF Tuning and Board Attach'
Short answer: a stamped shield can is a thin-metal enclosure, usually 0.15-0.30 mm tin-plated steel or a copper alloy, soldered or clipped over an RF circuit to contain electromagnetic energy and provide a clean ground return. The can is not just a lid — its cavity height, wall spacing and vent pattern are tuning elements that shift resonant frequency and shielding effectiveness. Get the ground-pad layout and can geometry right and you pass EMC without a ferrite or a board re-spin. Get them wrong and you chase emissions no firmware patch will fix.
Most engineers treat a shield can as packaging. It is not. At 1-6 GHz the can behaves as a resonant cavity and your vent slots behave as small antennas, so the mechanical drawing quietly sets electrical performance. This guide walks through what the can does, how geometry tunes it, what materials and plating to pick, and how to attach it to the board without wrecking yield.
What Does a Stamped Shield Can Actually Do?
A shield can does three jobs at once. First, it contains radiated emissions from a noisy circuit so the product passes EMC limits. Second, it shields a sensitive receiver from outside interference. Third, it gives the circuit a short, low-impedance ground return path through the board and the can walls.
That third job is where most designs fail. A can with sparse ground stitching is an antenna, not a shield. The general industry rule is simple: keep the spacing between grounding points below one-twentieth of a wavelength at your highest frequency. At 2.4 GHz the free-space wavelength is about 125 mm, so stitch spacing should stay at or under roughly 6 mm. At 5 GHz the wavelength drops to about 60 mm and the target tightens to around 3 mm. Those numbers are defensible starting points, not magic — verify with a near-field probe or a chamber sweep.
How Does Can Geometry Set RF Performance?
A closed rectangular can resonates at frequencies set by its internal dimensions. The lowest-order cavity mode scales with the longest internal dimension, so a larger cavity resonates lower. In practice you have two knobs: height and footprint.
Raising the can height lowers the lowest resonance, which is usually the wrong direction because you want the first resonance above your operating band. Flattening the can pushes resonance up. If you need a taller can for component clearance but cannot afford a low resonance, you break the cavity into compartments with internal walls or add grounded dividers — this raises the effective resonant frequency and improves isolation between the noisy part and the sensitive part.
Vent and cooling slots are a second tuning problem. A slot behaves as a slot antenna whose efficiency rises as its length approaches a half wavelength. Keep individual slot length short — under about one-twentieth of a wavelength — and orient long slots so they do not line up into one electrically long opening. Many shield cans fail only because three short vents on one face accidentally form a single long aperture.
| Parameter | Practical target | Why it matters |
|---|---|---|
| Ground-stitch spacing | ≤ λ/20 (≈6 mm at 2.4 GHz, ≈3 mm at 5 GHz) | Controls leakage; sparse stitching turns the can into an antenna |
| Single vent slot length | ≤ λ/20 | Long slots radiate; keep them short and staggered |
| Cavity height | Just clears tallest component + 0.2 mm | Flatter cans push first resonance higher |
| Wall thickness | 0.15-0.30 mm | Balances stiffness, cost and formed radius |
| Can-to-board coplanarity | ≤ 0.05 mm | Flat feet solder reliably; warped feet cause opens |
Materials and Plating for Shield Cans
Tin-plated steel (SPTE) is the workhorse because it solders well and costs little. Copper alloys such as C2680 brass or phosphor bronze form the spring fingers and clip features where you need contact force rather than solder. Nickel-silver (CuNiZn) is common for cans that must hold tight tolerances and resist corrosion without plating.
| Base material | Typical thickness | Plating | Best for | Notes |
|---|---|---|---|---|
| Tin-plated steel (SPTE) | 0.15-0.25 mm | Matte tin | Solder-down cans, high volume | Cheapest; watch tin whiskers on fine features |
| Brass C2680 | 0.15-0.30 mm | Ni + Au flash | Clip-on cans, spring contacts | Needs spring temper for finger force |
| Phosphor bronze | 0.15-0.30 mm | Ni + Sn or Au | EMI fingers, board-to-board | Best fatigue strength for repeated mating |
| Nickel-silver | 0.20-0.30 mm | Bare or Ni | Tight-tolerance frames | Corrosion resistant without plating |
| Copper C110 | 0.20-0.30 mm | Ni + Sn | High conductivity shields | Softer; strain-hardened tempers preferred |
Gold is not used for whole cans — it is too expensive. A nickel underplate with a thin gold flash on contact surfaces keeps contact resistance low and stable, which matters when the can is also serving as a grounding contact. For solderable feet, matte tin over nickel is the standard. Send the surface spec together with the drawing; plating choice, not stamping, is usually what decides long-term contact reliability.
Board Attach Options: Legs, Clips and Solder Pads
How the can meets the board decides assembly cost more than the stamping does. Four approaches dominate.
| Attach method | How it works | Board prep | Pros | Cons |
|---|---|---|---|---|
| Through-hole legs | Bent legs insert into plated holes and are wave/reflow soldered | PTH holes | Strong, low resistance | Consumes board area, blocks bottom-side routing |
| SMT solder feet | Flat feet reflow onto pads with the rest of the board | SMD pads + paste | No extra process step, pick-and-place compatible | Flatness is critical; poor feet cause tombstoning |
| Clip-on fingers | Can snaps over castellated or SMD fence | Fence/pads | Field-serviceable, removable | Needs spring temper and controlled finger force |
| Combined shield + frame | Stamped frame soldered down, lid clips on | Frame pads | Easy rework, good isolation | Two parts to manage |
For SMT cans the foot flatness and coplanarity target is typically 0.05 mm or better, and the can needs a flat pick area of at least 3 mm across for the nozzle. Where a can must be removable for rework, design a stamped frame that solders down permanently and a lid that clips into it — that keeps the sealing ground ring intact while letting you lift the lid.
Design Rules That Keep Assembly Clean
Keep a keep-out of at least 0.3 mm between the can wall and the tallest adjacent component so the can does not crush parts when it seats. Specify a generous formed radius — thin strip tears at sharp corners, and the die needs at least one material thickness of radius to form without cracking. Control burrs on the bottom edge, because a burr on a solder foot lifts the can and creates an open joint.
Design the vent pattern for tooling too. A slot pattern that looks clean in CAD may need a weak bridge in the die that breaks after a few thousand strokes. If you need many small vents, keep the bridge between slots at least 0.8 times the strip thickness so the punch stays strong.
If your project also needs stamped grounding clips, fingers or terminal hardware around the same board, it makes sense to source the whole family from one stamping line rather than split the tooling across suppliers. See how we approach EMI shielding contacts and stamped shields and enclosures for related design notes, or review the broader metal stamping process behind these parts.
Frequently Asked Questions
Q: What thickness of metal is used for a stamped shield can?
A: Most RF shield cans are stamped from 0.15-0.30 mm strip. Tin-plated steel at 0.20 mm is the common default; copper alloys run at the thicker end when the can includes spring fingers that need fatigue strength. Thicker material stiffens the can but raises forming force and cost, so pick the thinnest gauge that still meets coplanarity and finger-force targets.
Q: Can shield cans be attached with standard SMT reflow?
A: Yes. Flat-foot cans are placed by a pick-and-place nozzle and reflowed with the rest of the board, provided foot coplanarity is held to about 0.05 mm and the part has a flat pick area of at least 3 mm. Beyond that, the main risk is tombstoning from asymmetric paste, so balance the pad layout.
Q: How do I stop a shield can from resonating in my band?
A: Raise the first cavity resonance above your operating band by flattening the can or adding internal grounded dividers, and keep every vent slot shorter than about one-twentieth of a wavelength at your highest frequency. Ground stitching should also follow the λ/20 rule. Then verify with a near-field probe before you commit to the design.
Q: Do you hold tight tolerances on stamped shield cans?
A: We hold ±0.05 mm on formed shield-can features as a standard stamping tolerance, with tighter control on specific critical dimensions where the drawing calls for it. Because cans are deep-formed from thin strip, the practical limits depend on feature size and material, so we flag any dimension that would drive cost without adding function.
Q: What sample lead time can I expect for a new shield can?
A: Soft or bridge tooling for a prototype shield can typically ships samples in about 10-15 working days; a full progressive die for volume is longer. Send a drawing with material, plating and attach method, and BQUQ returns an indicative quote within 12 working hours, with real tooling and piece prices once the geometry is confirmed.
Related Resources
- EMI Shielding Contacts Guide: designing stamped fingers and contact points for shielding and grounding.
- Metal Stamping Service: progressive-die and short-run stamping for shield cans, frames and terminal hardware.
- About BQUQ: an ISO9001-certified source factory in Dongguan running stamping, CNC, springs, collets and heat sinks under one roof.
- Contact us: send your drawing to sc@bquq.com for a 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
