The medical device customer called us in April. They had just received a shipment of dome sheet arrays from us, and 3% of the sheets had a tiny scratch on the dome surface. The scratch was not deep - it was about 0.02mm wide - but it was enough to change the actuation force by 15 grams. On a medical infusion pump, where the button must feel exactly the same every time, that 15-gram variation was a problem.
We investigated. The scratch was not from the stamping process. It was from the packaging. Our operators were manually placing each dome sheet into a protective bag, and then sealing the bag with a heat sealer. During that process, the operator's fingernail would occasionally catch the edge of the dome, leaving a tiny scratch. The scratch was invisible to the naked eye, but it was measurable on the force tester.
We installed a fully automated packaging line in June. The scratch rate dropped from 3% to 0.1%.
What the old process looked like
Before the new line, every dome sheet went through four manual steps:
Step 1: An operator picks the dome sheet off the tray, using tweezers.
Step 2: The operator places the sheet into a 100um-thick anti-static poly bag.
Step 3: The operator folds the bag over, and seals it with a hand-held heat sealer.
Step 4: The operator labels the bag with the part number, batch number, and quantity, and puts it into a cardboard box.
Each sheet took about 15 seconds to package. An operator could package about 240 sheets per hour. The problem was not speed - it was consistency. Some operators were more careful than others, and the scratch rate varied from 1% to 5% depending on who was on the line. We also had a problem with contamination: the operator's gloves would leave tiny lint particles on the dome surface, which could cause intermittent contact.
Dome sheet arrays being fed into the automated packaging line, with zero human contact.
What the new line does
The new line is a fully automated reel-to-reel packaging system. The dome sheets come off the die-cutting machine on a carrier film, and they go directly into the packaging line without any human touching them.
The line has four stations:
Station 1: Cleaning. The dome sheet passes through an ionizing air knife, which blows off any dust or lint particles. The ionized air neutralizes the static charge on the film, so dust does not stick to the surface.
Station 2: Inspection. A camera looks at each dome sheet, checking for scratches, dents, or missing domes. If it finds a defect, it marks the sheet with a red dot, and the downstream operator can pull it out later.
Station 3: Packaging. The dome sheet is automatically fed into a pre-formed anti-static bag. The bag is sealed with a heat sealer, which holds the temperature at 160C ±5C, and the pressure at 0.3 MPa. The seal width is 5mm, which is wide enough to prevent leaks but narrow enough to not waste material.
Station 4: Labeling. A thermal printer prints the part number, batch number, and quantity onto a label, which is automatically applied to the bag. The label also has a QR code, which links to the inspection report for that batch.
Four-legged stainless steel domes sealed in anti-static bags, ready for shipment.
The numbers
The new line packages 1,200 sheets per hour, which is 5x faster than the manual process. The packaging time per sheet dropped from 15 seconds to 3 seconds. The scratch rate dropped from 3% to 0.1%. The lint contamination rate dropped from 2% to 0.05%.
We also reduced the number of operators on the packaging line from 6 to 1. The one operator is just monitoring the line, reloading the bags and the labels, and pulling out any defective sheets that the camera flagged. This freed up 5 operators to move to the stamping line, where we needed more hands.
The payback period on the new line was about 14 months, based on the reduction in scrap and the increase in throughput. That is faster than we expected.
What this means for our customers
If you order dome sheet arrays from us, you will now receive them in a sealed, labeled bag, with a QR code that links to the inspection report. You can scan the QR code with your phone and see the force curve, the salt spray test result, and the visual inspection photo for your specific batch.
This is especially important for medical and automotive customers, who need full traceability for every part. If you have a problem with a batch, you can scan the QR code and we can pull up the exact production parameters, the operator who ran the stamping press, and the packaging line settings. We can trace every dome sheet back to the raw material roll it came from.
We also offer custom packaging options: we can package the sheets in tape and reel, in waffle packs, or in custom trays. If you have a specific packaging requirement for your metal domes, FPC assemblies, or membrane switch panels, talk to our sales team. We will work with you to design the right packaging for your product.
- John Smith, Senior Application Engineer, Shanyo
