If I wave solder in the battery, it begins draining rapidly until the RTC chip (clock) is set. So I installed a jumper. Now I manufacture without the jumper, and then in the bed of nails testing, I set the clock and install the jumper before I package it and put it in stock. I never EVER want the jumper removed, but it is happening. Is there a way to make a lockable jumper or other ideas for a solution?
Could you wave solder in a battery holder instead, and install the battery later in your manufacturing process?
Here's an app note from TI about this sort of thing using their parts: https://e2e.ti.com/blogs_/b/powerhouse/archive/2014/06/05/maximize-shelf-life-with-a-one-time-push-button-switch
- conductive paint dabbed onto a SMD resistor footprint
- use a simple graphite pencil to shorten two pads (your RTC doesn't draw enough current, hopefully, to make these couple 100 Ω a problem)
- make through holes in the right distance. Use an office stapler to close the circuit
- big fat REMOVING THIS JUMPER DAMAGES THE DEVICE AND IS DETECTABLE silkscreen or neon sticker
- through-hole rivet
You could add an inexpensive SOT-23 or SC-70 MOSFET and a (say) 10M resistor and put the jumper in place to turn the RTC off.
There would be a drain of a few hundred nA, probably less than the battery self-discharge, until the jumper is removed.