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

7.1 Case Study 1: Humidity-Induced Positive RH Offset

Problem Statement

The customer implemented the HDC3020 on a PCB and observed a positive RH offset on a subset of devices compared to a reference during their post-assembly evaluation. Two affected units were returned to TI for analysis after being desoldered from the board.

Investigation Phase

The initial step was to test the returned devices in a controlled RH chamber across a range of humidity levels. Compared to known-good control units, the returned devices showed a consistent RH offset, but no gain error. Since the error was limited to an offset, the investigation focused on temporary moisture absorption rather than chemical contamination. This RH offset is shown in Figure 7-1.

HDC3020 with RH Offset Vs Known Good HDC3020 Figure 7-1 HDC3020 with RH Offset Vs Known Good HDC3020

Since this was only RH offset and not RH gain, the investigation focused on excess moisture absorption as the potential cause, instead of chemical contamination. To mitigate the suspected moisture-induced error, the sensors were baked at 100°C for 2 hours and retested. This baking successfully restored RH accuracy. If this had failed, a secondary bake at 100°C for 10 hours would have been considered. If the offset persisted, this suggests either permanent damage due to environmental stress or possible chemical contamination.

After baking the HDC3020, the sensor was able to have the RH offset removed. The customer's returned RH sensor had it's RH accuracy improve as seen in Figure 7-2.

HDC3020 with RH Offset Post Bake Figure 7-2 HDC3020 with RH Offset Post Bake

To find the root cause, the user needed to find differentiating information or steps taken between the HDC3020s showing this offset and those without offset. After ruling out lot differences or application differences, the user identified that all the sensors that were positively offset were being assembled at one particular manufacturer. That PCBA manufacturer may have been continually exposing the HDC3020 to high RH conditions (>70%) either during assembly or storage, leading to the positive RH offset.

Conclusions

  • The RH error was most likely caused by temporary moisture absorption during high-humidity assembly conditions.
  • Baking at 100°C for 2 hours effectively removed the offset.
  • All affected devices were traced to a single manufacturer, highlighting the importance of controlling humidity during sensor assembly.
  • Preventative action included implementing low-RH storage or avoiding high-humidity exposure during assembly.