32.768kHz RTC - Ultra Sonic Welding (USW) - how to verify "Phase Noise"/jitter ?

[hilper]

Hi
We are using a 32.768 kHz Real Time Clock (RTC), in an electronic product, we have under development.
The dimensions of our PCBA are approximately 30x25 mm.

The assembly method used to join the top & bottom plastic shells (enclosures), is Ultra Sonic Welding (USW).

The parameters for the USW process are (pls see the picture below):

Welding energy: 38.1 Ws
Max. power: 452 W
Power loss: 30 W
Frequency: 34953 Hz
Welding time: 142 ms
Welding travel: 0.24 mm


Do you see any problems in using the USW process ?

If yes, do you have any suggestions to how to verify that the RTC/"CRYSTAL UNIT" has been affected by the USW process ?


We are concerned about that the USW could harm/"degrade the performance (in terms of "phase noise"/jitter) of" the RTC.


Do you have any suggestions to how to verify the "phase noise"/jitter performance of the RTC ?

BR

[RoGeorge]

Compare the phase noise of the same unit before and after the ultrasonic welding.

Phase noise accumulates as time jitter.  Therefore, if you count many oscillations with a counter, then overflow edge will not fell always at the same moment, it will wiggle around the expected overflow moment, or else said it will show time jitter.  By looking at how widespread the jitter is around the expected counter overflow moment, before and after USW, one can tell if there was any performance degradation.

This is an unrelated example based on the same principle (phase noise accumulated as jitter in time), where the oscilloscope is triggered at t₀, then the counter overflow pulse (the one jumping back and forth on the oscilloscope's screen) is observed million counts later from t₀ (here is one second later).