Checking MEMS Device Compatibility Before Ultrasonic Cleaning

A populated sensor board may contain components that tolerate a cleaning chemistry but do not tolerate the associated mechanical energy or liquid exposure. Approving a cleaner by its compatibility with solder mask is therefore incomplete. Review the entire cleaning method against every sensitive device on the assembly.

Read the device-specific restriction

STMicroelectronics’ STHS34PF80 hardware implementation guidance prohibits ultrasonic cleaning for that infrared sensor because it can damage the MEMS structure. This is a concrete restriction for the named device. Other sensors require their own current handling instructions; the word MEMS alone does not define a single cleaning qualification.

Build a compatibility list using complete component identifiers. Include sensors, microphones, resonators, open optical devices, switches, and other parts whose packaging exposes a sensitive structure or port. Record the manufacturer’s permitted methods, explicit prohibitions, and unresolved conditions.

Describe the proposed process precisely

• Name the cleaning chemistry and concentration where applicable.
• State whether the assembly is immersed, sprayed, manually cleaned, or exposed to ultrasonic energy.
• Include temperature, exposure duration, rinse method, and drying sequence.
• Identify which device surfaces or openings may contact liquid.
• Record the stage at which sensitive parts are installed.

A statement such as ‘standard wash’ cannot be compared meaningfully with a supplier restriction. The cleaning contractor and design team need the same process description before qualification begins.

Resolve incompatible requirements early

If the board requires residue removal but a fitted sensor prohibits the intended wash, review process sequencing or an explicitly permitted alternative. Installing the sensitive component after a cleaning stage may be feasible, but the subsequent soldering operation introduces its own residues and handling requirements. Temporary masking also needs evidence that it protects the relevant feature without leaving contamination.

Do not treat a short functional test as permission to override an explicit manufacturer prohibition. A reading within limits immediately after cleaning may miss latent damage or drift. Obtain written device-specific guidance if the intended process falls outside published instructions.

The production traveler should make the restriction visible where cleaning is selected, not only in the design review archive. Include inspection or calibration steps appropriate to the sensor function and preserve pre-process reference measurements when they help detect change. Review compatibility again when the device variant, cleaning equipment, chemistry, or subcontractor changes. This keeps a successful qualification tied to the actual materials and process rather than to the board’s name alone.

Make the cleaning restriction available to external assembly partners before quotation and process planning.