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Here is a schematic of a surface mount coin cell holder, taken from the datasheet:

enter image description here

Presumably after it is soldered in place, you just slide the coin cell underneath the central part, with the positive side down, and with the positive line underneath the middle part of the holder, onto which the cell presses down to complete the circuit. The mounting tabs give the negative polarity.

But a few things don't make sense.

  • Why are there little holes in the tabs, which presumably are the mounting points - won't this just reduce the strength of the mounting?
  • The 'gap' into which to slide the coin cell seems to be only 0.41mm high, which is surely ridiculously thin for a coin cell - is the idea that the holder stretches up to accommodate it?
  • If so, what size coin cell will it accept, and why isn't this specified on the datasheet?
  • Doesn't this method of operation mean that there will be a lot of upward force on the contacts?
  • How will this ensure a good enough electrical connection to the positive terminal, if there is no solder used there?
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    \$\begingroup\$ According to the drawing you linked, that is just the "Coin Cell SM Negative Contact". "Negative Contact" probably implying there is another part called a "Positive Contact". \$\endgroup\$
    – Tyler
    Mar 7, 2017 at 18:14
  • \$\begingroup\$ Yeah looking at the height ( 0.2mm ) you'll have trouble sliding paper underneath it, let alone a coin cell... You need to find the other half as Tyler says. \$\endgroup\$ Mar 7, 2017 at 18:26
  • \$\begingroup\$ That's only half what you need. You need a clip that goes on top of that. There are much better one-piece solutions. But when you chose one, pick one that LOCKs in the battery, and does not just hold it with a spring. Esp. if it is something that is shipped with the battery in place. \$\endgroup\$
    – Trevor_G
    Mar 7, 2017 at 18:52
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    \$\begingroup\$ This question shouldn't be downvoted! The OP had a misunderstanding, and asked a well-formulated question to clear it up! That's what this site is for :) \$\endgroup\$
    – bitsmack
    Mar 7, 2017 at 19:17
  • \$\begingroup\$ Thanks everybody (except for the downvoter :)). Clearly only people who already know loads about electronics are allowed on this site. \$\endgroup\$ Mar 7, 2017 at 20:12

1 Answer 1

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Presumably after it is soldered in place, you just slide the coin cell underneath the central part

No, this is meant to replace the usual PCB pad. In some applications a PCB copper trace doesn't meet the requirements (perhaps it's the wrong plating, etc) so they place a component to act as the negative contact. This fits entirely under a typical side insertion coin cell holder, and is thin enough that in most applications you don't need a taller one - it adds pressure, which may be a good thing depending on the application.

Why are there little holes in the tabs, which presumably are the mounting points - won't this just reduce the strength of the mounting?

Not necessarily. The solder fillet that forms in the hole may add as much strength as a flat contact, but more importantly this allows for inspection of the solder joint. Further, this is the negative contact, and pressure will be applied from above, pushing it into the PCB. This won't undergo significant pulling strain.

The 'gap' into which to slide the coin cell seems to be only 0.41mm high, which is surely ridiculously thin for a coin cell - is the idea that the holder stretches up to accommodate it?

No, the cell goes above it.

what size coin cell will it accept, and why isn't this specified on the datasheet?

This works for many coin cell sizes, and isn't designed for a specific coin cell size.

Doesn't this method of operation mean that there will be a lot of upward force on the contacts?

Not applicable when used correctly.

How will this ensure a good enough electrical connection to the positive terminal, if there is no solder used there?

The positive terminal will have to be a separate piece, placed above this piece. During assembly you'll have two components installed at this location, first this negative terminal, then over that a positive terminal on different PCB pads.

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