Good vibrations

Robert Chittick of C-MAC Quartz Crystals, located in Essex, England, describes his company’s experience with a CO2 composite spray cleaning unit for removing submicron particles from piezoelectric crystal resonators during production.
Quartz crystal resonators (QCRs) are used in a myriad number of electronic devices and applications requiring precise timing.  QCRs vibrate at a fixed frequency when electrically excited.  QCR contamination results in poor stability and aging characteristics, and produces an effect called drive level dependence (DLD).  This means the activity of the QCR is non-linear with the applied drive level, and in extreme cases may not oscillate at all.  This is commonly called a sleeping crystal.  Thus removal of surface contaminations is critical to the functionality of QCRs and successful removal to produce a qualified timing device is indicative of successful removal of submicron contamination.  C-MAC tests proved that the CO2 composite spray technology could successfully reduce or eliminate DLD without damage to delicate QCRs.  Moreover the CO2composite spray cleaning technique allows for cleaning immediately following plating in their original containers, improving productivity of the cleaning operation.

Source: 
“Using CO2 Snow to Correct Drive Level Dependence in Quartz Crystal Resonators”, Precision Cleaning, June 1997