Author: John Smith, Applications Engineer at Shanyo.
A few months ago a hardware team in Shenzhen sent us a photo: a 12-key remote control where every other button felt mushy. They had designed the dome pads in-house, ordered our standard 12 mm snap domes, and assembled the array themselves. The problem was not the domes - it was the PCB pad layout. The center contact pad was 3 mm too wide, the ground ring was missing a 0.2 mm gap, and two vias landed directly under the dome's snap point. The domes were bottoming out on copper instead of clicking cleanly.
We see this pattern on roughly one out of four new design-ins. A metal dome is a precision spring switch. It does not care how pretty your PCB looks - it cares about pad geometry, clearances and copper-to-dome contact physics. Get the layout wrong and you get weak clicks, double-triggering, or early failure long before the rated 500,000 cycles. Below are the seven rules we hand to every new customer's hardware engineer before they release Gerber files.
1. Center contact pad: smaller than you think
The center pad is where the dome center touches to close the circuit. The most common mistake is making it too large. If the center pad covers more than about 30% of the dome's projected area, the dome cannot snap cleanly - it bottoms out and the click disappears.
For a standard 12 mm round dome, we recommend a center pad diameter of 2.5 mm to 3.0 mm. For a 6 mm dome, drop to 1.0 mm to 1.5 mm. The pad should be centered within ±0.15 mm of the dome's geometric center. Offset the center pad by 0.3 mm and you will feel it as an off-center click - the key still works, but the product feels cheap.
2. Outer ground ring: leave the snap gap
The outer (anode) contact ring needs to sit under the dome's rim, but it must not extend into the area where the dome flexes during snap. If the copper ring rises too far inward, it acts as a mechanical stop and kills the tactile ratio.
Our rule of thumb: the inner edge of the outer ring should sit 0.3 mm to 0.5 mm outside the dome's free-state rim. There should be a clear solder-mask-defined gap between the center pad and the outer ring of at least 0.2 mm. For sealed or low-signal designs, extend the ring slightly and add a gold contact spot - but keep the snap gap clean.
3. Dome-to-dome spacing: do not crowd the carriers
When designing a keypad array, it is tempting to pack domes as close as the key pitch allows. But each dome on a dome sheet array sits on a PET carrier, and that carrier needs room to breathe. Center-to-center spacing below 8 mm for 12 mm domes causes adjacent domes to interfere during snap - press one and the neighbour feels it.
Minimum center-to-center distance should be dome diameter + 2 mm. So 12 mm domes need 14 mm pitch; 6 mm domes need 8 mm. If your industrial design demands tighter pitch, move to a smaller dome size rather than squeezing the layout.
4. Vias: never under the snap point
This is the mistake that caused the Shenzhen remote-control failure. Vias are fine on a PCB, but no via, via barrel, or via tenting bump may sit directly under the dome's snap path. A via tent under the center point raises the copper by 0.1 mm–0.2 mm, which the dome feels as a hard stop. The click goes dead and the dome either stays closed or double-triggers.
Run vias outside the outer contact ring, or bury them beneath the solder mask with a flat tent. If routing forces a via near the pad, keep it at least 1.0 mm from the center pad edge and confirm tenting flatness with your board house.
5. Solder mask: define the pads, not the copper
Let the solder mask define the contact area. Do not rely on mask-to-copper registration to trim the pad - that tolerance is typically ±0.1 mm, which is enough to ruin a carefully calculated click ratio. We recommend:
- Solder mask opening on the center pad: pad size + 0.1 mm clearance on each side.
- Mask cover over the rest of the copper, including the area where the dome rim flexes.
- No mask sliver between center and ring that could peel and interfere after assembly.
For gold-plated pads (ENEPIG preferred), specify the contact finish only on the two contact zones - not the whole board - to control cost.
6. Adhesive area: the dome needs a home
Most consumer-electronics metal domes ship on a carrier with 3M 467 adhesive backing. The adhesive needs a flat, clean copper or mask surface to bond to. Do not place test points, silk-screen text or via stitching directly under the adhesive ring - any bump breaks the bond and causes the dome array to lift after temperature cycling.
We usually ask PCB designers to leave a 2 mm-wide ring of flat solder mask around the contact pads, dedicated to the adhesive. This is also where you want the dome array's alignment features to land.
7. Backlighting and cutouts: keep the light path clean
If your keypad has LED backlighting, the light needs to reach the keycap through gaps around the dome. Leave at least a 0.5 mm annular gap between the dome rim and the surrounding mask, and route the LED either off-center or in a dedicated light pipe. A dome directly over an LED creates a dark spot - the stainless steel blocks the light completely.
For high-end designs we pair the dome array with an FPC flexible circuit and a light guide film, which solves backlighting uniformly. If you are building a rigid PCB design, plan the LED positions on a cross-section before routing.
What we send with every dome array order
When you order custom domes from us, we do not just ship parts. The package includes:
- A recommended Gerber layer stackup with pad dimensions drawn to scale.
- A force-curve graph for the exact dome geometry you selected.
- An adhesive-bonding diagram showing the flat mask area.
- Salt-spray and RoHS certificates.
This is the difference between a supplier that sells stamped discs and a partner that designs with you. The Shenzhen team re-spun their board to our recommended layout, and the second assembly passed 100% of the click-feel checks. The remote shipped on schedule.
Check your Gerber files before you send them out
Before you commit a PCB run, open your Gerber viewer and ask: Is the center pad under 30% of the dome area? Is there a 0.2 mm gap to the outer ring? Are vias clear of the snap path? Is there a flat adhesive ring? Is backlighting routed away from the steel?
If any answer is "no", take another look. A 10-minute layout review saves a 4-week PCB respin and a missed launch window.
Need a second pair of eyes? Send us your Gerber files or a pad-layout screenshot. Our engineering team will flag any dome-interference issues - free, before you commit to tooling.
John Smith is an applications engineer at Qingdao Shanyo Precision Electronic Technology Co., Ltd., a metal dome manufacturer in Qingdao, China, supplying dome arrays, FPC circuits and silicone keypads to consumer, automotive and medical OEMs since 2004.
Author: John Smith, Applications Engineer at Shanyo.
A few months ago a hardware team in Shenzhen sent us a photo: a 12-key remote control where every other button felt mushy. They had designed the dome pads in-house, ordered our standard 12 mm snap domes, and assembled the array themselves. The problem was not the domes - it was the PCB pad layout. The center contact pad was 3 mm too wide, the ground ring was missing a 0.2 mm gap, and two vias landed directly under the dome's snap point. The domes were bottoming out on copper instead of clicking cleanly.
We see this pattern on roughly one out of four new design-ins. A metal dome is a precision spring switch. It does not care how pretty your PCB looks - it cares about pad geometry, clearances and copper-to-dome contact physics. Get the layout wrong and you get weak clicks, double-triggering, or early failure long before the rated 500,000 cycles. Below are the seven rules we hand to every new customer's hardware engineer before they release Gerber files.
1. Center contact pad: smaller than you think
The center pad is where the dome center touches to close the circuit. The most common mistake is making it too large. If the center pad covers more than about 30% of the dome's projected area, the dome cannot snap cleanly - it bottoms out and the click disappears.
For a standard 12 mm round dome, we recommend a center pad diameter of 2.5 mm to 3.0 mm. For a 6 mm dome, drop to 1.0 mm to 1.5 mm. The pad should be centered within ±0.15 mm of the dome's geometric center. Offset the center pad by 0.3 mm and you will feel it as an off-center click - the key still works, but the product feels cheap.
2. Outer ground ring: leave the snap gap
The outer (anode) contact ring needs to sit under the dome's rim, but it must not extend into the area where the dome flexes during snap. If the copper ring rises too far inward, it acts as a mechanical stop and kills the tactile ratio.
Our rule of thumb: the inner edge of the outer ring should sit 0.3 mm to 0.5 mm outside the dome's free-state rim. There should be a clear solder-mask-defined gap between the center pad and the outer ring of at least 0.2 mm. For sealed or low-signal designs, extend the ring slightly and add a gold contact spot - but keep the snap gap clean.
3. Dome-to-dome spacing: do not crowd the carriers
When designing a keypad array, it is tempting to pack domes as close as the key pitch allows. But each dome on a dome sheet array sits on a PET carrier, and that carrier needs room to breathe. Center-to-center spacing below 8 mm for 12 mm domes causes adjacent domes to interfere during snap - press one and the neighbour feels it.
Minimum center-to-center distance should be dome diameter + 2 mm. So 12 mm domes need 14 mm pitch; 6 mm domes need 8 mm. If your industrial design demands tighter pitch, move to a smaller dome size rather than squeezing the layout.
4. Vias: never under the snap point
This is the mistake that caused the Shenzhen remote-control failure. Vias are fine on a PCB, but no via, via barrel, or via tenting bump may sit directly under the dome's snap path. A via tent under the center point raises the copper by 0.1 mm–0.2 mm, which the dome feels as a hard stop. The click goes dead and the dome either stays closed or double-triggers.
Run vias outside the outer contact ring, or bury them beneath the solder mask with a flat tent. If routing forces a via near the pad, keep it at least 1.0 mm from the center pad edge and confirm tenting flatness with your board house.
5. Solder mask: define the pads, not the copper
Let the solder mask define the contact area. Do not rely on mask-to-copper registration to trim the pad - that tolerance is typically ±0.1 mm, which is enough to ruin a carefully calculated click ratio. We recommend:
- Solder mask opening on the center pad: pad size + 0.1 mm clearance on each side.
- Mask cover over the rest of the copper, including the area where the dome rim flexes.
- No mask sliver between center and ring that could peel and interfere after assembly.
For gold-plated pads (ENEPIG preferred), specify the contact finish only on the two contact zones - not the whole board - to control cost.
6. Adhesive area: the dome needs a home
Most consumer-electronics metal domes ship on a carrier with 3M 467 adhesive backing. The adhesive needs a flat, clean copper or mask surface to bond to. Do not place test points, silk-screen text or via stitching directly under the adhesive ring - any bump breaks the bond and causes the dome array to lift after temperature cycling.
We usually ask PCB designers to leave a 2 mm-wide ring of flat solder mask around the contact pads, dedicated to the adhesive. This is also where you want the dome array's alignment features to land.
7. Backlighting and cutouts: keep the light path clean
If your keypad has LED backlighting, the light needs to reach the keycap through gaps around the dome. Leave at least a 0.5 mm annular gap between the dome rim and the surrounding mask, and route the LED either off-center or in a dedicated light pipe. A dome directly over an LED creates a dark spot - the stainless steel blocks the light completely.
For high-end designs we pair the dome array with an FPC flexible circuit and a light guide film, which solves backlighting uniformly. If you are building a rigid PCB design, plan the LED positions on a cross-section before routing.
What we send with every dome array order
When you order custom domes from us, we do not just ship parts. The package includes:
- A recommended Gerber layer stackup with pad dimensions drawn to scale.
- A force-curve graph for the exact dome geometry you selected.
- An adhesive-bonding diagram showing the flat mask area.
- Salt-spray and RoHS certificates.
This is the difference between a supplier that sells stamped discs and a partner that designs with you. The Shenzhen team re-spun their board to our recommended layout, and the second assembly passed 100% of the click-feel checks. The remote shipped on schedule.
Check your Gerber files before you send them out
Before you commit a PCB run, open your Gerber viewer and ask: Is the center pad under 30% of the dome area? Is there a 0.2 mm gap to the outer ring? Are vias clear of the snap path? Is there a flat adhesive ring? Is backlighting routed away from the steel?
If any answer is "no", take another look. A 10-minute layout review saves a 4-week PCB respin and a missed launch window.
Need a second pair of eyes? Send us your Gerber files or a pad-layout screenshot. Our engineering team will flag any dome-interference issues - free, before you commit to tooling.
John Smith is an applications engineer at Qingdao Shanyo Precision Electronic Technology Co., Ltd., a metal dome manufacturer in Qingdao, China, supplying dome arrays, FPC circuits and silicone keypads to consumer, automotive and medical OEMs since 2004.
