The German engineer on the video call leaned forward and said, "We need a dome that survives -40C to 85C, 500,000 cycles, and 95% humidity. And we need it in a dome sheet array, not loose domes, because our assembly line is fully automated."
That was the kickoff call last November. The customer is a Tier-1 supplier of battery management systems (BMS) for European electric vehicle makers. They needed a dome sheet array for the service disconnect panel on the battery pack. The panel has six buttons: battery status, cell balance, thermal warning, service mode, manual disconnect, and reset. Each button has to feel the same, every time, for the life of the vehicle.
We shipped the first 500,000 pieces last week. This is our first production order into the European EV supply chain, and it took 11 months of qualification to get there.
What made this project different
Most consumer electronics dome orders take 2-4 weeks from RFQ to production. This one took 11 months. The reason: automotive qualification is not a one-time test. It is a sequence of design reviews, sample builds, environmental tests, and process audits.
The customer's engineering team flew to our Qingdao factory in February. They reviewed our die press process, our AOI inspection, our ESD controls, and our traceability system. They asked to see the SPC chart for actuation force over the last 3 months. They asked to see the calibration records for our force gauge. They asked to see the training records for the die press operators. We had all of it, which surprised them.
Battery management system service disconnect panel with our custom dome sheet array.
Then came the testing. We built three prototype batches of 5,000 domes each. The customer tested them at their lab in Stuttgart. They ran:
Temperature cycle - -40C to 85C, 100 cycles. The actuation force changed by less than 5g, within the ±10g spec.
Humidity storage - 95% RH at 85C, 1000 hours. Contact resistance stayed below 30 milliohms.
Life cycle - 500,000 actuations at 1N/s. The force decay was less than 15%, well within the 25% failure threshold.
Vibration - 10-2000Hz sweep, 10g acceleration, 8 hours per axis. No dome delamination, no intermittent contact.
We failed the first prototype batch. The vibration test caused intermittent contact on two of the six buttons. We traced it to a too-thin gold plating on the contact point (0.03um instead of the specified 0.05um). We re-plated the second batch at 0.05um, and it passed.
The dome design
The customer needed a 12mm round dome with 250g actuation force. That is heavier than the typical 160g consumer dome, because the button has to feel deliberate - a driver should not accidentally press the service disconnect while driving.
We used SUS301 full-hard stainless steel, 0.15mm thick, with a gold flash plating of 0.05um on the contact point. The dome sheet array is on a 0.125mm polyimide film with PSA adhesive, pre-laid on the customer's FPC.
12mm SUS301 stainless steel domes rated for 500,000 cycles in EV applications.
The array has six domes on a single 80mm x 60mm sheet. The spacing between domes is 12mm center-to-center, which matches the customer's FPC button layout. We laser-marked the lot number on the corner of the film, so every sheet is traceable to the raw material coil and the die press run.
What this means for Shanyo
This order is significant for us because it proves that our metal domes can meet automotive-grade requirements. We already had IATF 16949 certification, but this is the first time our parts have been designed into a European EV program. The customer has a forecast of 2.5 million domes per year, running through 2030.
We are also applying the same process discipline to our other automotive customers. We now run all automotive orders through a dedicated production line, with first-article inspection on every shift, SPC charting on actuation force, and full lot traceability.
If you are designing an EV battery pack, a charging station interface, or an industrial control panel that needs FPC-mounted dome arrays or membrane switch panels, talk to our engineering team. We can qualify your application in 8-12 weeks, and we support automated assembly with dome sheet arrays that feed directly into your SMT line.
- John Smith, Senior Application Engineer, Shanyo
