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

7.2 Case Study 2: Gradual RH Accuracy Drift in 100%RH Environment

Problem Statement

The HDC3022 was deployed in three outdoor environments: urban, coastal, and mountainous. All devices initially met RH accuracy specifications. However, over a period of two to three months, devices showed RH accuracy degradation, failing to reach full 100% RH during high humidity conditions. For example, one sensor remained at 90% RH despite ambient humidity reaching 100% as seen in Figure 7-3.

HDC3022 RH Error at 100% RH Dropping Over Time Figure 7-3 HDC3022 RH Error at 100% RH Dropping Over Time

Investigation Phase

As the devices operated within the specifications prior to deployment, early-stage causes such as PCB layout, assembly, or rehydration were ruled out. Although environmental exposures varied across the three locations, the symptoms were consistent, suggesting a shared root cause.

Despite prolonged exposure to 100% RH typically causing a positive RH offset, these sensors exhibited the opposite: reduced maximum RH readings. This pointed to an obstruction rather than polymer saturation. Baking the devices at 70°C and 10% RH for 6 hours restored RH accuracy, confirming a recoverable error.

The likely cause was determined to be dust accumulation on the PTFE filter, which inhibited moisture ingress. This hypothesis was formed by process of elimination, given that chemical contamination was unlikely due to the RH being accurate during initial deployment and the different application environments making it difficult to identify a common exposed chemical. The improvement after baking suggested that the accumulated dust was partially removed, allowing the sensing polymer to rehydrate.

Figure 7-4 is a representation of the root cause identification process, demonstrated on the RH Accuracy Debugging Flowchart:

RH Accuracy Debugging Flowchart Case Study 2 Example Figure 7-4 RH Accuracy Debugging Flowchart Case Study 2 Example

Conclusions

  • A low-temperature baking step improved performance by clearing the obstruction.
  • The issue was not tied to chemical contamination from VOCs or assembly quality.
  • Enclosure design improvements can reduce future dust ingress by reorienting air intake so that dust cannot arrive to the HDC3022.
  • Since oven access is impractical for fielded devices, the integrated heater is recommended for periodic use.