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HDC2010: higher than expected sensor to sensor variation, non compliant humidity measurements

PrasadP
Prodigy 190 points
Part Number: HDC2010
Other Parts Discussed in Thread: HDC2080

Matt,

It appears we had some information about the critical assembly mentioned in the document.

But we do not know where is the point of error as of now.

Actually we designed a PCB with 6 HDC2010 sensors to characterize the variation. Fig (1)

Also the few boards we populated was possibility units from different batches of HDC2010.

Attached are the initial scatter plots - we see (hugely) non compliant measured values  Fig. (2)

Can this amount of drift be expected from assembly mishap in your experience?

Also - What would you suggest as next step to solve this issue?

Confirm assembly procedures are done well once again ? (we are prepping to re-assembly another set) 

Also Is there an evaluation board/kit which we can use to retest & characterize sensor to sensor variation ? May be buy few eval boards and retest?

Please let me know your thoughts.

Prasad

Fig(1) PCB we have used, 3 such PCBs left in free air and such that all devices measure humidity at almost the same instant.

Fig(2): Sensor to sensor variation scatter plots

  • 0
    Prodigy 190 points
    Edit:
    Sorry a new post was created by mistake. Below is original reply to my post mentioned above.

    Matthew Sauceda wrote the following post at Thu, Sep 6 2018 1:37 PM:
    Hi Prasad,

    Thanks for the update. Humidity Sensors in general have to go through a strict fabrication flow to reduce any possibility of contamination that may occur during this process. The guidelines are provided in the following link, and are typically found in the product tool folder:

    www.ti.com/.../snia025

    If these guidelines are not followed, contaminates or VOCs that are common in the assembly process may impact device accuracy, as the polymer dielectric is fully exposed to the environment.

    Best Regards,
    Matt
  • 0 in reply to PrasadP
    TI__Genius 11750 points
    Hi Prasad,

    Thanks for the clarification. Yes, I believe it may be worth it to verify the fab and assembly process for your board. The document I've mentioned in the previous posts should help, but I would like to highlight main points when designing with humidity sensors:

    1. Ensure that the type "no-clean" solder paste is used when soldering the HDC devices.
    2. Board washes are not allowed after the HDC device is placed onto the board. This is especially important, as any chemical/liquid wash will seep into the sensor area and impact the performance of the sensor.
    3. The HDC device should be the last device populated on the PCB.
    4. Correct soldering profile should be used, and should not exceed 260C.

    We do have some EVMs that you can order for the HDC2010 and HDC2080 devices. The EVMS can be found at their respective product tool webpage. Please let me know if you have difficulty finding the page.

    Best Regards,
    Mat
  • 0 in reply to Matthew Sauceda
    Prodigy 190 points

    Hi Matt,

    Would you recommend a suitable assembly house familiar with HDC2010 assembly?

    We have a next batch made as per instructions by another assembly house.

    But this new batch also has issues, but better - Any help appreciated.

    PS: We can send these boards to you - so you can confirm assembly issues.

    Regards,

    Prasad

  • 0 in reply to PrasadP
    TI__Genius 11750 points
    Howdy PrasadP,

    It may be best to call them directly and direct them towards the storage and handling guidelines document found on the product page of the device.

    Best Regards,
    Matt