Hi Ingemar,
I sure hpe it says 6-10 grms, not grams. If it says grams than the document
got over-edited by staff thinking this is a typo. grms stands for 'g', the
Earth gravitational acceleration constant and rms stands for
root-mean-square, and is standard vibration terminology.
This is an effective ESS procedure for finding solder joints with latent
defects, and comes from some of the old military vibrational requirements.
The full details you would have to get from one of the vibration gurus, I am
not one of them.
In addition, be careful with superBGAs, they warp at high power dissipation
and can cause tension induced SJ failures.

Werner Engelmaier

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