Electronics > Manufacturing & Assembly

Automated assembly of CR2032 coin cell to PCB

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VintageHenk:
I'm designing a relatively high volume (~500k), very low cost CR2032-powered board that needs a flush bottom side and will go inside a potted enclosure.

Normally you would just do a reflow for the SMT parts, use a THT tabbed CR2032, a second pick-and-place round for the battery and wave solder it to the PCB, but as the bottom needs to be (relatively) flush, I can't have the battery leads sticking out. I'm also trying to avoid the cost of using a battery holder as the battery isn't replaceable anyway. I'd preferably use something like the SMT-tabbed coin cell in the attached image but that would need to be hand soldered (?), which isn't great at these volumes. I have also found sheet metal formed side entry coin cell holders (see attached image for an example) that can meet my cost targets, but I don't think a pick and place machine can shove the cells in sideways, so that would require expensive labor and/or a jig, which again isn't great.

How would you guys and gals go about automating the attachment of the battery cell to the PCB? Any secret tricks of the trade? I'm still in the design phase, so everything is open.

Kean:
At those volumes you should be discussing options with a battery supplier rather than looking at existing off-the-shelf offerings.
They would have seen similar requirements before, and can likely offer some custom termination and packaging to better suit mass production.

Kean:
Further thought
As reflow isn't compatible with batteries, and wave soldering isn't going to work for your requirements - maybe conductive glue on the top-side pads before placing the tabbed cell.  The dispensing and placement can all be automated pretty easily.  I'm guessing the current demands on the battery are pretty low so the joint resistance isn't a huge problem, and the potting will add extra mechanical strength so you wouldn't need to fully rely on the conductive glue.

David Hess:
Normally I would suggest using the flat battery holder on the top even though the battery will never be replaced, but potting a battery holder risks having the potting material push on the mechanical connections enough to disconnect the battery.

Is there any safety issue with venting when a battery is potted?

Is there an alternative to a coin cell battery which would be more suitable?

Psi:
Avoid using any method that uses a PCB pad as one of the battery contact. Such as in your 2nd pic.

It's very hard to get it to work reliably. The connection tends to go bad and become high resistance. Combine that with the fact you're using a CR2032 that already has pretty high internal resistance and you have a recipe for lots of failed products. Or products that think the battery is low when it's still ok.

Best to find a tabbed cell that will work, either TH or SMT.

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