> I have a small project that uses a couple of coin cell battery holders:
> http://uk.farnell.com/keystone/3003/retainer-coin-cell-20mm-pk5/dp/908654
>
> The negative contact is provided by a pad about a third the area of the
> battery on the PCB.
> Space is quite tight, so I was thinking about running some traces
> underneath the battery near the negative contact.

I have no exactly specific experience, and it would depend on the mask
material, and I'd expect an epoxy two pot mask to survive well BUT I'd stil=
l
be highly wary of doing this. It looks like being well within the range of
things that Murphy excels in being good at.

By putting an unrelated track under the contact area you are introducing a
masked track to compete with the unmasked contact. If the contact is using
immersion gold or something else very thin the track + mask could end up
higher than the contact and preferentially take the contact pressure.

An "obvious" [tm] solution seems to be to build up the contact height 'ever
so slightly". Either roller tin or some purposeful extra plating or even an
actual contact shim etc.

Two very thin wires say 75% or so of the contact width apart and terminated
somewhere convenient in vias/holes just outside the battery fotoprint would
allow the battery to "sit up on rails above the pcb surface
When rendered in Courier New the following makes an ugly diagram of the
above, but it's unlikely to be needed.

BBBBBBBBBB
BBBBBBBBBB   Battery
 CCCCCCCC     Contact
  o    o        Wires
PPPPPPPPPP       PCB

Two or one strip of thin shim may be kinder to the cell. May be able to be
soldered at end nearest push in direction only. May.

Battery manufactuer have differing ideas of how wide the centre contact is.
Figures of 16, 17 and 17.7 mm can be found for a CR2032 cell.

Your holder    http://www.farnell.com/datasheets/15138.pdf

Wikipedia CR2032    http://en.wikipedia.org/wiki/CR2032_battery

Very nice links page to CR2032 from many manufacturers    http://cr2032.co/

Sony 17mm    http://cr2032.co/datasheets/sony-cr2032-datasheet.pdf

Duracell - don't know and draftsman was drunk (see 20mm dimension arrow)
http://cr2032.co/datasheets/duracell-cr2032-datasheet.pdf

Energiser 17.7mm  http://cr2032.co/datasheets/energizer-cr2032-datasheet.pd=
f

Varta - shoulder dimension <> contact width?
http://cr2032.co/datasheets/varta-cr2032-datasheet.pdf

Panasonic 16mm    http://cr2032.co/datasheets/panasonic-cr2032-datasheet.pd=
f

Maxell - go away    http://cr2032.co/datasheets/maxell-cr2032-datasheet.pdf
Some nice others specs.


    Russell McMahon
    Applied Technology ltd.












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