A medical device buyer told us their startup had saved money by ordering loose individual domes instead of pre-laminated dome sheet arrays. The first 500 units went out by hand assembly, and the per-dome price looked attractive. When they ramped to 20,000 units a year and tried to place the domes on their SMT line, the pick-and-place nozzle kept picking two domes at once because the parts were loose in the tape, and about six percent of the boards came out with a dome flipped over or shifted sideways. A flipped dome looks fine on the outside but never collapses. By the time they added inspection, rework and a custom feeder, the "cheaper" loose domes cost more per finished panel than the array ever would have.
That story is the whole subject of this guide. When you source metal domes, you have two supply formats: a pre-laminated dome sheet array, where the domes are held in exact position on a carrier film ready to peel-and-place onto the PCB, or loose individual domes supplied on tape and reel for your own SMT line. The two formats look like the same part at the supplier catalog. They are not. They differ on per-unit price, assembly equipment, alignment consistency, rework rate, minimum order quantity and which production volume they actually fit.
If you are comparing dome suppliers, planning an OEM keypad program, or deciding whether to buy domes loose and assemble them yourself, the comparison table and scenario framework below show which format fits your volume, your line, and your product.
What the two formats actually are
A dome sheet array is a carrier film - usually polyester or PET - with every dome pre-positioned in the exact pattern of the customer's PCB. The array ships as a sheet or reel, and the assembler peels off the backing, aligns the whole sheet against the board, and presses it on in one placement. Every dome lands where the engineering drawing says, because the holes in the carrier film are punched to ±0.05mm.
Loose individual domes are the same SUS301 parts, supplied one at a time on tape and reel. They are fed through a pick-and-place machine that picks each dome, places it on the adhesive or pad, and moves to the next. There is no carrier film; alignment depends on the feeder, the nozzle and the board reference. For low volumes, a technician places them by hand with tweezers.
A pre-laminated dome sheet array aligned to the PCB contact pattern; all domes land in one placement.
Dome sheet array vs loose individual domes: comparison table
| Parameter | Dome sheet array (pre-laminated) | Loose individual domes (tape and reel) |
|---|---|---|
| Per-dome unit price | Slightly higher (carrier film added) | Lower base price |
| Placement method | Peel-and-place whole sheet in one step | SMT pick-and-place, one dome at a time |
| Alignment accuracy | Held to ±0.05mm by punched carrier holes | Depends on feeder and nozzle; typically ±0.15–0.25mm |
| Rework rate on assembly | Under 1% once aligned | 3–8% depending on line maturity |
| Minimum order quantity | Higher; tooled carrier for the layout | Lower; standard reel parts available |
| Setup time for new layout | Carrier film tooling, days to first sample | Feeder/nozel setup on SMT line, hours |
| Inventory flexibility | Layout-specific; cannot reuse on another board | Standard domes; reusable across designs |
| Labor per panel | One sheet placement, fast | One pickup per dome, slower |
| Best-fit volume | 5,000 panels per year and up | Below a few thousand, or high-mix low-volume |
| Main limitation | Carrier tooling cost; overkill for prototypes | Requires SMT feeder tuning; alignment drift at high speed |
How each format behaves in production
Dome sheet arrays remove the placement problem from the customer's line. Because the carrier film fixes the relative positions of every dome, the assembler only has to align the sheet once against two board reference marks. There is no per-dome feeder, no nozzle changeover, and no chance of picking two domes at once. The trade-off is that the carrier film is tooled to one specific board layout; the array cannot be reused on a different keypad. For a product that runs for years at volume, that fixed tooling is a strength, because every production run repeats the same alignment. For a prototype or a one-off, the tooling cost is wasted.
Loose individual domes are the flexible, low-commitment option. The same reel of 12mm round domes works on several different customer boards, which suits a contract assembler building small batches of many products. The cost per dome is lower because there is no carrier film. The catch is that loose domes have to be handled by equipment that is tuned to them: a feeder that separates one dome at a time, a nozzle that picks a thin stamped part without flipping it, and a placement head accurate enough to land the dome on a small contact pad. Getting that tuning right takes time, and until it is tuned the rework rate climbs. This is exactly what happened on the medical ramp.
Loose four-legged SUS301 domes on tape and reel, fed through a pick-and-place for high-mix assembly.
Scenario framework: which format for which product
High-volume fixed-layout production - choose dome sheet arrays. Automotive interior switches, appliance keypads, medical handhelds and consumer remotes that run for years at tens of thousands of units per board layout benefit most from the pre-laminated array. The alignment is fixed, the line labor drops, and the rework rate falls below one percent. The carrier tooling is paid back within the first production months.
Low-volume prototypes and pilot runs - choose loose domes. A first article, a small pilot of a few hundred panels, or a one-off custom build does not justify tooling a carrier film. Loose domes placed by hand or on a basic SMT feeder let the buyer test the design without committing to array tooling. This is the right format while the layout is still changing.
High-mix, low-volume contract assembly - choose loose domes. An assembler building ten different keypads for ten customers, each at a few hundred units a year, cannot tool a carrier film for every board. Standard loose reels that work across layouts are the practical choice, and the per-dome price stays low.
Precision and safety-related panels - choose arrays. Where a misaligned dome causes a double trigger or a dead key in a safety-relevant product, the ±0.05mm carrier alignment beats the ±0.15–0.25mm of a tuned feeder. Automotive safety buttons, medical infusion pump keys and industrial interlock panels all justify the array on reliability grounds, not just cost.
Curved or thin FPC-based panels - choose arrays on FPC. When the keypad sits on an FPC flexible circuit rather than a rigid PCB, loose domes are almost impossible to place reliably because the flexible substrate moves under the nozzle. We supply FPC panels with the domes pre-laminated at our factory, which is the standard way to build those products.
Checklist: parameters to agree before ordering
1. Annual volume per board layout. The crossover point where array tooling pays back is roughly 5,000 panels a year. Below that, loose domes are usually cheaper once assembly labor is counted; above it, the array wins on rework and labor.
2. Panel layout and dome pattern. If the keypad layout is stable and will not change, an array is sensible. If the layout is still being revised, wait for the design to freeze before tooling a carrier film.
3. Your assembly line capability. Loose domes need a feeder and nozzle tuned to thin stamped parts. If you do not have that equipment or the time to tune it, the array removes the requirement entirely. If you already run a fast SMT line with the right feeders, loose domes are efficient.
4. Dome geometry and size. Very small domes, four-legged shapes and cross domes are harder to place loose than large round domes. The smaller or more shaped the dome, the more the pre-laminated array earns its cost, because feeder misplacement rises with geometry complexity.
5. Contact finish and environmental rating. Both formats can carry silver, carbon or gold contacts; the choice of finish is independent of the supply format. Agree the contact finish and the PCB pad finish together, regardless of whether the domes arrive loose or on an array.
Common selection mistakes
The first mistake is choosing loose domes on price alone, without counting the cost of feeder tuning, inspection and rework. The medical startup's story is the textbook case: the per-dome saving disappeared under rework. Always compare the landed cost per finished panel, not the catalog price per dome.
The second mistake is tooling an array before the layout is frozen. If the contact pattern moves during prototype revision, the carrier film has to be re-tooled, and that cost lands on the buyer. Wait until the board layout is final before committing to the array.
The third mistake is assuming an array fits any SMT line. A peel-and-place array needs the operator to align the sheet against board marks, not a standard pick-and-place feeder. Make sure your assembly process can handle a sheet placement, or ask us to supply the array already laminated onto the FPC or PCB at our factory.
The fourth mistake is ignoring the dome geometry. A 12mm round dome is easy to place loose; a small four-legged 5mm dome flips in the feeder. Match the format to the geometry, not just to the volume.
How we verify alignment and contact on both formats
For arrays, we measure dome position under a microscope after lamination and confirm every dome sits within ±0.05mm of its target on the carrier, and we sample actuation force on each key to ±10g. For loose domes, we supply parts to the same dome specifications and run sample reels on a reference feeder so the customer's line can tune against a known-good part. Both formats are shipped with contact resistance and plating thickness data, and both can be paired with silicone buttons and membrane switch overlays as a complete stack.
Shanyo supplies both formats: loose individual domes in standard geometries for high-mix and prototype work, and pre-laminated dome sheet arrays for volume and precision programs. Send us your panel layout, annual volume and assembly line capability, and our engineering team will recommend which format fits, supply a sample within 48 hours for standard geometries, and quote factory pricing for custom OEM or wholesale programs. Contact Shanyo to discuss the right dome supply format for your product.
The cost crossover, shown with numbers
To make the choice concrete, run the math on a 16-key keypad. Loose domes might cost a fraction more per piece in catalog terms, but every panel needs 16 pick-and-place placements, feeder monitoring, and a post-placement inspection step. At a six percent rework rate, roughly one panel in seventeen comes back for repair. Arrays cost a few percent more per dome because of the carrier film, but the whole 16-key sheet lands in one placement, and the rework drops under one percent. At 5,000 panels a year, the saved labor and avoided rework usually covers the carrier film tooling; below that volume, the tooling does not amortize and loose domes win. At 50,000 panels a year, the array is cheaper per finished panel by a clear margin, and the alignment consistency also improves field failure rates.
Inventory is the other hidden factor. A reel of loose domes is a general-purpose part that can sit on the shelf for any future design. A tooled array is specific to one board layout and becomes dead stock if that product is cancelled. Buyers running many small programs often prefer loose domes for that reason alone, even when the per-panel math slightly favors the array. We will quote both formats on the same RFQ so the buyer can see the trade-off on their own numbers rather than choosing on a hunch. Most customers settle on a split: loose domes for prototype and low-volume SKUs, arrays for the high-volume production SKU once the design is fully frozen and validated in the field.
- John Smith, Senior Application Engineer, Shanyo Precision Electronics, Qingdao
