ultrasonic welding effects on gyros

Hi,

We're using ultrasonic welding to assemble the plastic housing our circuit sits in. The circuit has an ITG3200 on it. About half of the assembled circuits end up not working - with not working meaning that the gyro stops reacting to rotation. We see values on the three axes that vary by about 4 from their current value, and show no reaction to any motion.

Is this a matter of finding an appropriate frequency for the welding machine, or is ultrasonic welding a non-starter for these gyros?

thanks