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HDC1080: HDC1080 humidity accuracy

Noriaki Fukazawa
Expert 1620 points
Part Number: HDC1080

Dear Jose-san,

In the past, Fukasawa received Jose-san special support on the humidity accuracy of HDC 1080.
We are continuing QA with customers, but we have not solved it.
Please let me ask a question again.

<Situation>
An HDC 1080 is mounted on a mass production board of a customer.
This board is called a board A.
However, humidity accuracy errors occurred on some board A.

Therefore, exactly the same size as  board A,
board  B composed of the same parts was prepared.
The customer has identified the cause by comparing board A and board B.

※ Board size = 0.4 cm × 1.3 cm
    Configuration = HDC 1080 + 1 capacitor only

However, an error of + 5% steadily occurs in the humidity accuracy
measured on the  board B.
Also, as a result of allowing the  board B to reflow again and then leaving it,
it was possible to confirm the result that the accuracy recovered.
(Reflow is recommended only once. Customer is known)


<Question>
① We don't understand why the difference between board A and B occurs although
    both of their production conditions are same.
    Could you list possible cause?

② If the reflow temperature is low, is there a possibility of an accuracy error of 5%?

　Because accuracy restoration was confirmed when re-reflow was applied.

 

Best,Regars.
Fukazawa

  • 0
    TI__Genius 11750 points
    Howdy Fukazawa-san,

    Thank you for the post and information. I have a few questions about the test setup and environment.

    1) Did the customer perform a humidity profile on the devices to determine accuracy? If so, what was the humidity range for characterization?

    Page 5 of the datasheet, footnote (11), states that the recommended humidity operating range is 10% to 70% RH. Prolonged exposure outside this range will result in measurement offset, which will affect the accuracy of the device.

    One experiment to try is to slightly bake another set of boards that display the issue. If the offset is corrected, the root cause may be exposure above the range above, or possible contaminants affecting the polymer of the device, which would affect the accuracy.

    Best Regards,
    Matt
  • 0 in reply to Matthew Sauceda
    Expert 1620 points

    Hello Matt-san,

    Thank you for your reply!!

    Please let me ask a few questions.

    <Questions>

    1,What is a humidity profile? Where is it in the data sheet?

    2,>>>One experiment to try is to slightly bake another set of boards thatdisplay the issue.

    What does it mean to bake the board?

    Re-reflow or directly warm the sensor part with fire?

    3,Are there factors other than long-term exposure and contaminants outside the

    recommended humidity range that affect humidity detection accuracy?

    Regardless of the magnitude of influence, I want to identify factors one by one.

    In addition, we attach a list of actual humidity detection errors. Give me advice.

    I appreciate your kind work.

    Best Regars.

    Fukazawa

    HDC1080 Humidity error.xlsx

  • 0 in reply to Noriaki Fukazawa
    TI__Genius 11750 points

    1,What is a humidity profile? Where is it in the data sheet?


    The humidity profile simply refers to a humidity sweep, did they test the device in a humidity chamber to determine humidity accuracy? Please let us know their setup conditions.


    2,>>>One experiment to try is to slightly bake another set of boards that display the issue.
    What does it mean to bake the board?


    The sensors may need to go through a re-hydration procedure after soldering. Can the customer leave the sensor for a couple of days at 40-70% RH to verify that the sensor is brought back to it's specified state?


    Conditions that lead to low or high humidity or exposure to solvents can also affect the sensor. There is one procedure that might bring the sensor back to it's calibrated state, and that is by performing a bake and re-hydration. Please note that the customer should employ safe handling procedures to prevent exposure to contaminates and solvents, as the below procedure is not guaranteed to work and is more of a guideline of what to try when the sensor is exposed to extreme conditions and solvents.
    1. Baking the IC at ~100C <5% for 5-10hrs
    2. Re-hydration: ~30C at 60-75%RH for 6-12hrs

    3,Are there factors other than long-term exposure and contaminants outside the recommended humidity range that affect humidity detection accuracy?

    This information can be found in the following document: Humidity Sensor: Storage and Handling Guidelines

    Best Regards,

    Matt

  • 0 in reply to Matthew Sauceda
    Expert 1620 points

    Hello Matt-san,

    Thank you for your special support.
    Please let me ask a question again.


    <Question1>
    >>The humidity profile simply refers to a humidity sweep,
        did they test the device in a humidity chamber to determine humidity accuracy?
        Please let us know their setup conditions.

    Q.
    The humidity setting of the customer is measured at humidity 50% to 60%,
    and it is within the recommended range of HDC 1080.

    We will also investigate the time you left HDC 1080 if you need information.
    Also, are there any other necessary setting conditions?


    <Question2>
    >>There is one procedure that might bring the sensor back to it's calibrated state,
    　and that is by performing a bake and re-hydration.

    Q.
    If reflow is applied under the correct conditions and then left to stand, humidity accuracy deviates by 5%
    Even after leaving it for several hours, the deviation of humidity accuracy of 5% does not change.

    However, when we swept the moisture by baking, the humidity accuracy recovered.
    When left for several hours, the recommended humidity accuracy remains within the range of 1% to 2%.

    At the moment of reflowing, there is an error in humidity accuracy,
    although moisture should be flying,

    It is impossible to understand the mechanism by which the accuracy recovers
    once it is left to bake again.

    As a result, the cause of the accuracy error remains unknown,
    Even if a humidity accuracy error occurs, if you restore accuracy by baking,
    Is it okay to recognize that it is not a defective item?



    Question is much troublesome.
    Please lend me some wisdom to solve the problem.

    Bets,Regars.
    Fukazawa

  • 0 in reply to Noriaki Fukazawa
    TI__Genius 11750 points

    Hi Fukazawa,

    Please instruct the customer to try the following that was suggested and provide results:

    The sensors may need to go through a re-hydration procedure after soldering. Can the customer leave the sensor for a couple of days at 40-70% RH to verify that the sensor is brought back to it's specified state?

    If this does not bring the accuracy to the level that is specified in the datasheet then it may point to something affecting the accuracy during assembly. Please instruct the customer to follow the Humidity Sensor: Storage and Handling Guidelines that was provided above.

    And as suggested above the bake is only suggested for use if the polymer is exposed to any contaminants and chemicals during the re-flow process.

    Additionally, the layout of the board can also impact performance, so please ensure that the customer receives the following document:
    Optimize placement and routing: www.ti.com/.../snaa297a.pdf

    Best Regards,
    Matt

  • 0 in reply to Matthew Sauceda
    Expert 1620 points
    Dear Matt-san,

    Thank you for your special support.
    I'm sorry for the late reply.

    > Please instruct the customer to try the following that was suggested and provide results:
    > The sensors may need to go through a re-hydration procedure after soldering.
    > Can the customer leave the sensor for a couple of days at 40-70% RH to verify
    that the sensor is brought back to it's specified state?


    I confirmed that you suggested me.
    The customer said as follows.

    Humidity accuracy of HDC1080 on "board B" was deviated +5 % after the first reflow for mounting.
    He subjected "board B" on which HDC1080 was already soldered to the second reflow.
    And after the second reflow, he left "board B" under high humidity environment (40 to 70 %RH) for several days.
    Then the humidity accuracy of "board B" was recovered within ±2 %.


    Now considering the above I have additional questions.

    <Question>
    1. Is it OK to apply the second reflow and re-hydrate to recover the humidity accuracy of HDC1080?

    2. Can he use the board which is applied the second reflow and re-hydration to mass production?

    3. Is there any concern of the second reflow and re-hydration such as follows?
    - Damage of polymer.
    - Recovering of the humidity accuracy is temporary, and deviation of
    accuracy would be appeared again after using for a while. etc.


    Best regards,
    Fukazawa
  • 0 in reply to Noriaki Fukazawa
    TI__Genius 11750 points

    Hi Fukazawa-san,

    <Question>
    1. Is it OK to apply the second reflow and re-hydrate to recover the humidity accuracy of HDC1080?

    • This may put added stress on the polymer, and it is not what we recommend on the datasheet.  After the first reflow, the board may need to sit in a humidity environment suggest above for several days to recover.  Please also note, the +-2% is a typical value, and many external sources may contribute to error, such as exposure to contaminants or board layout.

    2. Can he use the board which is applied the second reflow and re-hydration to mass production?

    • That is up to the customer's discretion, our datasheet states that the device should be limited to one reflow. Relaxation in a high humidity environment for several days to recover accuracy on a device.

    3. Is there any concern of the second reflow and re-hydration such as follows?

    • This is answered above.

    Best Regards,

    Matt

  • 0 in reply to Matthew Sauceda
    Expert 1620 points

    Dear Matt-san.

    Thank you for your answer for me.

    I understanded that can't more second time reflow and re-hydrate to recover the humidity accuracy of HDC1080.

    Please tell me about baking and re-hydration.
    I understand that baking and re-hydration execution is effective as a method of returning the sensor to the calibration state.

    <Condition>
    1. Baking the IC ~ 100 C <5% for 5-10 hrs
    2. Re-hydration: ~ 30 C at 60-75% RH for 6-12 hrs
    ※Absolute Storage Temperature＝-65~150℃


    <Question>
    ■How many times can you baking and re-hydrate to restore the humidity accuracy of the HDC1080?

    ■Can he use the board which is applied the many times baking and re-hydration to mass production?

    ■Are there the following concerns by repeatedly baking and re-hydrating to restore the humidity accuracy of the HDC1080?
    - Damage of polymer.
    - Recovering of the humidity accuracy is temporary, and deviation of
    accuracy error would be appeared again after using for a while. etc.


    Thank you for your special support many times!!

    Best,Regars.
    Fukazawa

  • 0 in reply to Noriaki Fukazawa
    TI__Genius 11750 points

    Howdy Fukazaw-san,


    1. There is not a definite answer as each time the device is baked, the polymer may experience microcracks and allow small pockets of liquid water to form and increase capacitance, therefore affecting accuracy.


    2. This is a decision for the customer as our datasheet recommends one reflow and a re-hydration period.


    However, if second reflow or bake-rehydration is performed, the customer would need to verify that the performance meets their production standard.


    3. This is covered in the answer to question 1.

    Best Regards,

    Matt