Battery Holder Footprint (Repost)

[SolarSunrise]

Hello again. I am currently designing a device that is powered from two LR44 coin cell batteries. The data sheet from the battery holder manufacturer says I need minimum 4mm by 4mm copper pad for the negative contact (check image below).

But won't this create an unstable connection? The diameter of a standard LR44 is about 11mm. The height of the plated copper would be lower than the surrounding solder mask(or is it?), thus the bottom of the coin cell won't contact the pad. Unfortunately the data sheet has absolutely nothing related to solder mask expansion and all the important bits. Do I have to make a HUGE solder expansion to keep the solder mask out?

The reason I'm really picky here is because as always, there's nothing more excruciating than having a production run of 1000 faulty boards... And this is my first design that had coin cells (never had to use one of these boys before). Just trying to avoid Murphy.

Thanks a lot guys!

Note: This is a repost to the General PCB Descussion. The original was in the Altium section, which I can't remove!

[peter.mitchell]

mind linking the datasheet for the specific battery holder? i cant wrap my head around it with the info provided.

[sleemanj]

The reason I'm really picky here is because as always, there's nothing more excruciating than having a production run of 1000 faulty boards... And this is my first design that had coin cells (never had to use one of these boys before). Just trying to avoid Murphy.

Go to tool box, collect calipers, measure battery.

I think the battery negative has a raised portion,that may be 4x4,then again, 4x4 is just the MINIMUM.  Doesn't mean you can't go bigger.

[peter.mitchell]

If this is a LR44 holder with a insulator like this

Just make a nice big pad in the center until it "looks about right", if you have a bigger pad it'll be more likely to make contact, even if uneven.

heres a quick footprint i whipped up that "looks about right" https://dl.dropboxusercontent.com/u/677635/lr44.PcbLib

[SolarSunrise]

Thanks guys! Unfortunately, I did few tests and concluded that this specific battery holder was very unstable. You really need a raised negative battery contact for the holder to be reliable. I ended up using a CR2032 battery holder from MPD (check attachments), which was much more reliable. Had to use an extra op amp to split the power supply into +/-1.5v though...

So the conclusion? Don't use these cheap metal frame holders but instead, use a battery holder that has a separate negative and positive contacts.

[miceuz]

errr... wouldn't putting solder paste on this 4x4mm pad solve the problem?

[peter.mitchell]

errr... wouldn't putting solder paste on this 4x4mm pad solve the problem?

not really; the potential for un-evenness is higher.

[kizzap]

Keep any copper not connected to that pad out of the connector, use soldermask peelback.