SNAA427 October   2025 HDC3020

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction: Why RH Sensors Appear Out-of-Spec
    1. 1.1 Where and When do RH Errors Occur?
    2. 1.2 What are the Root Causes of RH Errors?
    3. 1.3 Case Studies
  5. 2Definitions: Key Terms for RH Accuracy
  6. 3Initial Troubleshooting Steps
    1. 3.1 Initial Verification Steps
    2. 3.2 Diagnostic Questions
  7. 4Common Sources of RH Error - Prevention and Mitigation
    1. 4.1 PCB and Enclosure Design Considerations
      1. 4.1.1 PCB Thermal Transfer to RH Sensor
      2. 4.1.2 Power Supply Noise and Analog RH Sensors
      3. 4.1.3 Enclosure Design & Airflow Considerations
    2. 4.2 Assembly, Soldering, and Manufacturing Processes
      1. 4.2.1 Assembly Instructions: What to Avoid
      2. 4.2.2 Assembly Instructions: Best Practices
      3. 4.2.3 Sensor Cavity Protection During Assembly
    3. 4.3 Rehydration Post-Assembly
      1. 4.3.1 Recovering Sensor Accuracy Post-Soldering
      2. 4.3.2 Rehydration Procedure
    4. 4.4 Test Setup and Environment
      1. 4.4.1 RH References
      2. 4.4.2 Setup Uniformity: Controlled Environment
      3. 4.4.3 Setup Uniformity: Thermal Gradients
      4. 4.4.4 Settling Time
    5. 4.5 Storage and Handling
      1. 4.5.1 Storage Temperature and Humidity Conditions
      2. 4.5.2 Storage Materials
      3. 4.5.3 How Does MSL Level Relate to RH Sensors?
      4. 4.5.4 Handling Best Practices
    6. 4.6 Chemical Contamination
      1. 4.6.1 How Chemical Contamination Affects RH Accuracy
      2. 4.6.2 Where and How are Chemical Contaminants Introduced?
      3. 4.6.3 Mitigating Effects of Chemical Contamination: Bake
      4. 4.6.4 Mitigating Effects of Chemical Contamination: Cleaning
      5. 4.6.5 Mitigating Effects of Chemical Contamination: Enclosure Design
      6. 4.6.6 Mitigating Effects of Chemical Contamination: Device Selection
      7. 4.6.7 Mitigating Effects of Chemical Contamination: Assembly Considerations
    7. 4.7 Operating Conditions: Application Environment Conditions and Effects
      1. 4.7.1 Environmental Conditions That Contribute to RH Accuracy Errors
      2. 4.7.2 RH Offset Mitigation & System-Level Design
      3. 4.7.3 Using the Integrated Heater
    8. 4.8 RH Accuracy Debugging Flowchart
  8. 5Summary: Designing for and Debugging RH Accuracy
  9. 6References
  10. 7Appendix
    1. 7.1 Case Study 1: Humidity-Induced Positive RH Offset
    2. 7.2 Case Study 2: Gradual RH Accuracy Drift in 100%RH Environment
    3. 7.3 Case Study 3: Combined Factors from Assembly & Thermal Effects

5 Summary: Designing for and Debugging RH Accuracy

RH sensor accuracy can be affected by multiple contamination sources throughout the production and deployment process. This document outlines strategies to eliminate or mitigate error sources across assembly, handling, and system integration. Whether diagnosing an existing issue or designing a new application, following a systematic process improves reliability and accuracy in RH sensing.

Looking back at Figure 1-1 and , the design timeline illustrates how many potential vectors there are for RH accuracy errors to be introduced. Starting the design process with this in mind will allow users to eliminate risks in the areas they can control. RH accuracy matters because users need their RH sensors to last as long as possible in the field and deliver the right result to the end-user. That is why it is imperative for users making designs with RH sensors to understand the RH error sources and eliminate as many as possible before RH accuracy issues appear.

Table 5-1 Summary of RH Error Sources and How to Prevent/Mitigate Them
RH Accuracy Error Source What is causing RH error? How to mitigate & prevent RH errors
PCB & Enclosure Design PCB and/or enclosure design that does not allow RH sensor to sense ambient temperature and humidity accurately. Use PCB layout techniques that optimize ambient air sensing, and enclosures with unrestricted airflow.
Soldering & Assembly Non-recommended reflow profiles and assembly materials that cause chemical contaminations or damage. Follow recommended solder reflow profile and use assembly materials without VOCs and other potential contaminants.
Rehydration Skipping or deviating from datasheet rehydration profiles. Follow datasheet rehydration instructions.
Testing Testing RH sensors without a calibrated reference, without sufficient temperature and humidity settling time, testing in an uncontrolled environment, and not taking into account test chamber errors like thermal gradients. Test RH sensors with a calibrated reference inside a RH chamber, following manufacturer recommendations for settling time and temperature gradient compensation.
Storage and Handling Damaging or contaminating RH sensors during handling, storing at extreme humidity conditions or in the presence of off-gassing chemical contaminants. Handle RH sensors with vacuum pens and store RH sensors in metalized ESD bags in low temperature and low humidity conditions away from direct light exposure.
Chemical contaminations RH sensors have their sensing polymer's dielectric properties altered by unwanted chemicals. Identify potential sources of chemical contamination by examining production process and looking at the MSDS of different materials to look for potentially problematic chemicals. Mitigate existing chemical contamination with the integrated heater or an external oven for baking.
Operating conditions in application environment Operating continuously in extreme humidity conditions. Use the integrated heater periodically to bake out excess water vapor that accumulates over time in the sensing polymer to prevent RH errors from becoming too large.