On 13/10/2011 15:03, RussellMc wrote:
> 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 st=
ill
> be highly wary of doing this. It looks like being well within the range o=
f
> things that Murphy excels in being good at.

These were pretty much my thoughts too - I know solder mask is generally=20
pretty tough (from experience scraping it off to probe traces etc) but=20
Murphy is bound to ensure that a few percent have problems, for instance=20
if someone uses a sharp implement to push the old battery out when=20
changing batteries and accidentally scrapes a bit of the mask off.
I will ask my PCB house if they have any suitable coating that can be=20
added in that area.

>
> 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 usin=
g
> immersion gold or something else very thin the track + mask could end up
> higher than the contact and preferentially take the contact pressure.

This is an excellent point, will see what could be done about this also.

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

Yep, another question for PCB house.

> Two very thin wires say 75% or so of the contact width apart and terminat=
ed
> somewhere convenient in vias/holes just outside the battery fotoprint wou=
ld
> allow the battery to "sit up on rails above the pcb surface

Interesting idea, another thing to consider, thanks.


--=20
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