Cleaning RH sensors is a delicate procedure that should only be performed by experienced personnel. It is only effective in cases of visible solid or liquid contamination on the sensing polymer; cleaning cannot remove gaseous contaminants such as off-gassed VOCs. Figure 4-10 illustrates how to use a swab to clean the top of the sensing polymer. Manual cleaning poses a risk of damaging the RH sensor, so it should not be done as the first troubleshooting step.

Cleaning a sensor manually can siginificantly improve deposited chemical contaminants, but should only be used for troubleshooting purposes. If cleaning is done on a large quantity of devices, the risk of damage to the sensor increases significantly. Cleaning should be used to identify if a deposited chemical is causing RH accuracy errors so that the chemical can be avoided in production or end-application environments.

Figure 4-10 HDC Manual Cleaning Example

The following steps describe the procedure to safety clean the sensing cavity of RH sensors:

• Do not use chemical cleaning agents such as PCB wash or isopropyl alcohol.

• Lightly moisten a cotton swab with distilled water. The swab should be damp but not dripping.

• Gently clean the interior of the RH sensor cavity. Avoid direct pressure with the sensing polymer, wipe as lightly as possible.

• Ensure no residual water remains inside the cavity.

• Avoid spilling water onto the sensor's sides, which could lead to electrical shorts on the PCB.

• Dry the sensor using low-pressure compressed air directed across the surface.

• Do not use ultrasonic baths, as submersion and vibration can damage the sensor and lead to water ingress under the device, especially if the thermal pad is not soldered.

• Use a microscope to observe the sensing polymer, and observe if any solid contaminants were removed.