SNAA427 October   2025 HDC1010 , HDC1080 , HDC2010 , HDC2021 , HDC2022 , HDC2080 , HDC3020 , HDC3020-Q1 , HDC3021 , HDC3021-Q1 , HDC3022 , HDC3022-Q1 , HDC3120 , HDC3120-Q1

 

  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

4.5.3 How Does MSL Level Relate to RH Sensors?

A common source of confusion regarding storage conditions is MSL level. MSL stands for Moisture Sensitivity Level, and is a storage rating that informs users under what conditions an IC can be stored. Table 4-1 shows the different MSL levels.

Table 4-1 Factory Floor Life at 30°C
MSL Floor Life Moisture Relative Humidity
1 Unlimited 85% RH
2 1 year 60% RH
2a 4 weeks
3 168 hours
4 72 hours
5 48 hours
5a 24 hours
6 Bake before use and reflow within time on label

TI's RH sensors are rated MSL-1, meaning the sensors can be stored indefinitely in the packaging without affecting mechanical reliability. However, MSL rating pertains only to package integrity, not sensing performance.

For example, storing a sensor at 30°C/85% RH for one year can preserve package quality, but degrade RH accuracy due to moisture ingress into the polymer. Therefore, sensors must be stored in cooler (20°C - 30°C), drier (30%RH to 50%RH) environments than the MSL rating suggests.

More information on MSL can be found in MSL Ratings and Reflow Profiles.