Ultrasonic Cleaning of PCB’s with Crystals

Ultrasonic cleaning is a common method for cleaning electronic components and printed circuit boards (PCB). It uses high-frequency waves (usually running around 40 kHz) to agitate the cleaning liquid, thereby forcing the contaminants to be removed. Is there any risk when using ultrasonic cleaning on PCBs with crystals?

As a general rule, crystals in the MHz range such as LFSPXO056215REEL from IQD
should not be damaged during ultrasonic cleaning. Although the overall frequency and specifications must be considered, higher frequencies use thinner quartz blanks, and thicker low-frequency devices are more likely to break.

However, the risk to “tuning fork” technology used to produce low frequency crystals (such as the common 32.768 kHz crystal, LFXTAL073264REEL) is much higher. In applications, these crystals are designed to work at very low drive levels. Its internal architecture is designed to excite resonance at a very low input power level, which means that higher power levels are more likely to cause physical damage than other products. The frequency used in ultrasound is very close to the resonance frequency of quartz, which further increases the possibility of self-resonance.

Thus it can be seen that the use of ultrasonic cleaning on quartz products containing PCB is not without risks. For low frequency crystals in the kHz range, ultrasonic cleaning is not recommended. For other types of crystals, you may need to test your cleaning solution to evaluate the risks before using it in production.

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