Metal-Dome Contacts on PCB Pads: Specify Both Surfaces

Record the dome surface and PCB surface separately

For the dome record, name the supplier, part, base material, contact face and any finish applied to that face. Do not infer the contact-side coating from a marketing photograph or from a similar part number. For the PCB record, name the fabricator's exact contact-pad finish, the controlled pad artwork and the fabrication revision. Mark where the dome actually touches the pad and whether the drawing leaves an exposed, accessible contact area.

Then add the controller: a closure that works for one input circuit is not automatically acceptable for another sensing threshold or environment. Have the OEM define its closed/open electrical behavior, relevant voltage/current or sensing method and the owner of acceptance limits. Record intended inactivity, contamination or exposure conditions when they are part of the application. A dome change, pad-finish change or controller change can each alter the question the sample must answer.

In its dome-plating guide, Snaptron discusses unplated stainless steel and nickel, gold, silver and tin options for its own domes. It warns that the mating PCB or flexible-circuit finish, contamination, actuator alignment and life requirements also affect the complete contact. Gold on a dome is not automatically a mechanical-life improvement. These are supplier application considerations, not a recommendation that HYR uses any named finish.

Read pad-finish guidance within its supplier boundary

Start with the actual dome/PCB design, target electrical behavior and planned environmental/cycle checks. Ask the responsible dome and PCB suppliers what pad finishes they support for those conditions. 'Nickel,' 'hard gold' and 'ENIG' describe different constructions and processes; an RFQ should not collapse them into the word 'gold.' State which document and revision controls each candidate finish, and ask what board-fabrication evidence will be supplied.

Do not copy a supplier's plating-thickness table directly into an unrelated HYR BOM. A finish can satisfy its own deposition specification while the assembled dome still lacks a verified electrical-closure result. Likewise, a standalone dome force curve does not measure the resistance of the mated board contact. Request the finished sample and the electrical method that the buyer actually needs.

For its metal-dome/PCB examples, Snaptron's design page recommends nickel or hard gold pad plating for most applications and says ENIG may be suitable in lower-cycle uses only after application review. It ties finish selection to contact stability and expected switch life. That conditional recommendation belongs to Snaptron's designs; it is not proof that one of those finishes is universally required, that ENIG always fails, or that an HYR product meets a specific cycle rating.

Keep ENIG specification scope separate from switch life

Electroless nickel/immersion gold (ENIG) names a printed-board surface finish, not a synonym for a hard electroplated gold contact. If a proposal cites a finish standard, record its edition, board fabrication scope and the claimed conformance evidence. Identify the actual pads and whether the board supplier can provide the required deposit, process-control and inspection records. The OEM still needs a dome-to-pad application decision.

Do not use an ENIG finish designation as a universal pass/fail result for repeated dome impacts. Define the mated specimens, mechanical actuation, electrical conditions and environment before comparing one pad option with another. An electrical reading should say which key, when it was taken, the controller or measurement circuit, the mounted state and the acceptance criterion; otherwise two numbers may not be comparable.

IPC-4552B, issued April 2021, covers ENIG on printed boards and explicitly lists contact finish among its applications. Its publicly available scope and contents address deposit thickness, process control, contact surface and finish limitations. The document does not thereby certify a particular membrane-switch build, dome pairing or cycle-life target. Its coated-board scope also does not transfer to screen-printed PET contacts.

Compare two hypothetical quotes without inventing a pass

Imagine an OEM receives Proposal A naming a metal dome but listing only 'gold PCB' and Proposal B naming a dome contact-side finish and an ENIG board finish. These are hypothetical documents, not actual HYR quotations or tested combinations. Proposal A lacks a defined board process and possibly a defined dome contact face. Proposal B describes more of the interface, but still gives no evidence that its ENIG pad meets the chosen dome supplier's application advice or the OEM's finished-switch criteria.

Ask each proposer to return the exact dome grade, contact-side treatment, pad finish/process, substrate platform, pad drawing, controller conditions and mounted-sample test method. For any ENIG proposal, ask the responsible suppliers to explain why it is appropriate for the planned use and how the board finish will be controlled. A hard-gold alternative likewise requires its own exact process and sample evidence; neither the more expensive word nor a different color is an automatic pass.

Place both proposals into the worksheet below. If one lacks a contact-side record, mark that as missing; if the electrical limit is unknown, ask the OEM to define it rather than allowing a vendor default to become the specification. Compare only the same mounted drawing revision and intended environment. The output is a decision-ready evidence request, not a ranking of unmeasured materials.

Challenge five interface handoff failures

The following are hypothetical specification and test gaps, not observed HYR defects or customer cases. Each points to a missing decision or a sample that could answer it.

• Only the dome's gold finish is recorded. Add the actual PCB pad finish, contact geometry and board revision before describing the mated interface.
• The PCB quotation calls ENIG and hard electroplated gold equivalent. Request separate finish definitions and supplier application review; do not treat a shared color as shared wear behavior.
• A printed-PET contact is assessed using a PCB ENIG deposition document. Identify the true circuit platform and choose evidence applicable to that material and process.
• A clean new sample closes once, so the proposal claims a target cycle life. Define baseline and conditioned electrical checks on a representative mounted assembly with a project-selected cycle and environment plan.
• A dome or pad supplier is changed while the title of the RFQ stays the same. Update both surface records and review whether electrical, actuation, contamination and cycling evidence must be repeated.

Send a paired-contact RFQ and request mounted evidence

Give the converter and OEM board team one controlled drawing package: dome key position, PCB contact pads, spacer and vent details, actuator and housing support, circuit input and connector boundary. Attach the proposed dome and board-finish documents by exact grade and revision. Mark which supplier owns each material and process record, and name the OEM owner who can accept a change or unresolved deviation.

Specify an evidence sequence rather than assuming a finish label closes the question. First confirm each incoming component and pad finish against its applicable specification; then measure the identified mated assembly at baseline; finally run the selected conditioning, cycling and electrical follow-up that fits the application. Agree on measurement method, sampling, specimens, numeric criteria and disposition before inspecting a result. This is a proposed buyer workflow, not an HYR released test protocol.

For an HYR engineering inquiry, send the controlled drawing and the open dome/pad pairing questions through the secure RFQ. Ask for human project review of the construction and acceptance plan. No supplier's standalone guide or parent-company reference photo substitutes for the OEM's mated-sample evidence.