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HDC3022: HDC3022DEJR positive humidity offset

Tuomas Tissari
Prodigy 45 points
Part Number: HDC3022


Tool/software:

Hi,

We are experiencing an offset issue in the humidity measured by HDC3022DEJR.

We have been using HDC3022DEJR to measure the humidity and temperature of flowing air at flow rates between 1-10 liters per minute. Out of 31 samples that we've tested, 22 fell within ±2.5% of the humidity reported by set of two calibrated reference sensors. The nine unfortunately were off but varying degree, with some samples by as much as 14%. All of our samples tend to report elevated humidities in comparison to our reference sensors.

Below are two images from a test where we compared three samples to a set of two reference sensors.


Above is a graph representing humidity data from during the test.

Above is the recorded temperature data during the same test.


Even though the humidities we observed are always above the ones reported by the reference sensors, to debug the situation we performed the 5 day soaking period at 50%rH 25C, which is recommended in the datasheet of HDC3022. Images of it's effect below.


Above image compares the humidity reported by one of the samples (focused test, different test run) to one reference sensor before the soaking process.


Above is the same test process being applied to the same device, but where the sensor has been changed to another, and soaking was performed.

While it is at this point still inconclusive whether the change we saw in the focused test was due to the soaking process, or the change of the sensor, we'd be happy to receive any insight into the issue why this of a large percentage of sensors seem to disagree, by various degree, with the reference sensors.

Thank you for your insight.


Best Regards,

Tuomas Tissari

  • 0
    TI__Genius 12695 points

    Hi Tuomas,

    I want to ask you a few questions to better understand the nature of your issue.

    1. Can you share some details about the storage? Were these parts taken straight from a reel to PCBA then testing? Were they stored for any length of time in between those steps? If so, in what temperature and humidity conditions? Were they stored in bags, and if so, what kind? LDPE material, or metallized ESD bags?
    2. Do you have the lot information or NIST IDs for these parts? I can check internally to make sure they looked OK during our production test.
    3. I see that this data appears to be about ~40%RH for the test condition, were any other RH levels evaluated? If so, do you see the same RH error at every humidity level checked, or does it change?
    4. Was no-clean solder paste used during the PCBA, and was any board cleaner used? If so, could you share the MSDS so that I may evaluate if any chemicals that can cause contaminations (which will affect RH accuracy) are present?

    In the HDC3022 datasheet, baking is also mentioned as the first step for errors like this, then follow that with the 5 day soaking period. Was the bake attempted? If so, did it help the RH results at all?

    Regards

    -Alex Thompson

  • 0 in reply to Alex Thompson
    Prodigy 45 points

    Hi Alex,

    Thank you for getting back to me so quickly.

    I just wanted to let you know that we've read your reply and are now in talks with our ems to figure out the details. We will reply here as soon as we have gathered all of the information you requested.

    To point three; we are currently beginning a test in which we perform testing in varying temperature and humidity conditions.

  • 0 in reply to Tuomas Tissari
    TI__Genius 12695 points

    Tuomas,

    Thank you, please share all the details when you have them. Polymer-based humidity sensors can have their RH accuracy shifted by a variety of things, so tracing down root cause is always a little tricky. Given that about two thirds of the parts are working well for you, I doubt the issue is rooted in your testing methods or PCB design. Can you think of anything these failing devices were exposed to that the good parts were not? UV light? Unique chemical exposures?

    Thanks

    -Alex Thompson