HDC2010EVM: About how to store

Tachibana-san, 

Yes, there are directives and guidelines for the storage and handling of these devices. Were these devices tested in a socket or assembled on boards and then checked? If assembled, were the boards washed or exposed to any chemicals? What you describe we have seen and it sounds like the boards may have been washed or re-hydrated in some way during assembly.

How long after assembly were the boards tested? 

You can also bake the boards, too. This is what you did equivalent of when you used the heater this way, to discharge the excess moisture. I have seen this as well in the lab here. So 

From the product page http://www.ti.com/product/HDC2010, you can then view the datasheet in section 10.1.1 http://www.ti.com/lit/ds/symlink/hdc2010.pdf

where all the main guidelines are located. Also in the Design Resources for you section of the product page there is a link to an application report entitled: Humidity Sensor: Storage and Handling Guidelines http://www.ti.com/lit/an/snia025/snia025.pdf 

Hello Wyatt-san,

Thank you for the information.

Our customer evaluated HDC2010EVM which had been already assembled by TI.
The customer didn't solder HDC2010s, re-hydrate or wash HDC2010EVMs.
Just storing the HDC2010EVMs in their package for 4 months shifted the error of humidity.

So the customer is asking if there are special cautions about their storage.

Sincerely,
M. Tachibana

Hi Wyatt-san,

Thank you for the information.
I found the following information that the HDC2010EVMs have been washed.
e2e.ti.com/.../3088736

The customer has already operated the heater function for 48 hours and then left them for 12 hours to refresh.

Are there any special precautions regarding storage after refreshing?

Sincerely,
M. Tachibana

Hi,Wyatt-san,

I am very sorry, but I have additional questions.

[Questions]
1. The serial number of the HDC2010EVMs that the customer purchased are as follows.
Could you check if these ten EVMs were washed?
1209376, 1209379, 1209405, 1209415, 1209416,
1209600, 1209601, 1368079, 1368118, 1368963

2. For these ten HDC2010EVMs, the humidity accuracy was within the specification range just after purchase by the customer.
If these EVMs has been washed during the assembling process, how long does it take that humidity accuracy has become worse?

3. Again, the customer still think that the accuracy of the humidity has decreased because the customer was storing EVMs in a hot and humid environment like summer in Japan.
In the previous response, you said that there are no special treatment other than the handling method described in the datasheet or application report.
However, the customer is not convinced.
Since there are hot and humid periods in Japan, the customer believes that a way to avoid moisture from adsorbing to the humidity sensor might be necessary.
Could you please give us some advice?

Sincerely,
M. Tachibana

Tachibana-san, 

I believe its very possible all the HDC2010EVMs were washed as I found some ambiguity in an assembly document that had not been changed since the release of the EVM that has now been made very specific and communicated to the assembly house directly so the problem can be avoided when we build more.

We have removed all what we had in our stock and reworked them by baking them. This was all corrected about a month ago so not sure here on the timing of when they ordered and received these or the distribution source of the EVMs this customer procured. I saw the issue on multiples these units at first power up, which is what led to then finding the root cause of the issue. 

I would expect they should have seen the issue in the same way I did, and if they feel they have exposed the devices for a prolonged time to high temp and humidity outside the normal operating range of the device, then we do have in section 10.1.1.5 the basic bake and re-hydration procedure, which it sounds like they understand how to do. 

To help them further - I think we would need more details on how they are testing, against what reference, what conditions are (ambient office area, chamber), under what conditions do they think are extreme for their application - is this above 60C and 85%RH? (for one example) - for how long, etc.      

Hello Wyatt-san,

The customer purchased HDC2010EVMs in April 2019.
Since you said EVMs reworked last month (in September 2019), so I also think the EVMs of the customers may have been cleaned.

If so, can you explain any mechanism or cause for the following phenomenon?
"When measured just after purchase, the humidity accuracy of HDC2010EVMs were as per the specifications of Datasheet.
But after storing in the package for about 4 months in his laboratory, the humidity error of them increased to +6 ~ 9%. "

Sincerely,
M. Tachibana

In this case I don't know how they tested them to begin with, how they stored them and then how they tested them a second time, so I cannot speak to why they did not see the elevated levels before that. This was not my experience when i ordered units from our warehouse to test, when this issue initially arose.  

Hello Wyatt-san,

Thank you for your comment.

The customer measured the ambient humidity in his laboratory.
Then he compared the humidity data with the customer's reference hygrometer and confirmed the error.
After the measurement, he put the EVMs back in thier packing and stored in the laboratory.
And after four months, he measured the humidity in the same way and confirmed the error.

The customer have refreshed his EVMs with the heater function.
So we asked them to watch the progress after refreshing.

Sincerely,
M. Tachibana

Dear M. Tachibana - 

if I understand correctly, they saw the error out of the box, which I was saying was more or less expected, since we have discovered the boards were washed. And the boards still had the error, which was removed by baking them with onboard heater - this all sounds correct. 

Hi Wyatt-san,

I'm sorry to trouble you because of my repetitive questions. 
Information from the customer is as follows.

[Humidity accuracy of HDC2010EVM]
- Measured just after unboxing for the first time after purchase
    -> +1 to + 2 % (within the spec range)
- Measured after storage for 4 months in original box 
    -> +6 ~ +9 %

== Storage conditions ==
The average temperature for 4 months is about 23.4 °C and the average humidity is about 66 %.
Cumulatively about 1/4 of this period (760 hour) , the humidity exceeded 80 %.
Furthermore In this middle of July, it was stored for about a week continuously under an environment with a temperature of 25 °C and a humidity of more than 80 %.

Despite the washed EVM, the humidity error was within specifications when just after unboxing.
The customer is concerned whether it is normal behavior or not that the error to increase from +1 ~ 2 % to +6 ~ 9 % after storage in the original packing with the above conditions for 4 month.

Sincerely,
M. Tachibana

Hi Wyatt-san,

I will ask you a question again since there is no reply from you.

You said that normal HDC2010 or unwashed HDC2010EVM requires no special treatment other than what is described in the datasheet or application report.

Are the following storage conditions within the normal handling range that you said?
Or is it a storage condition that requires baking?

== Storage conditions ==
The average temperature for 4 months is about 23.4 °C and the average humidity is about 66 %.
Cumulatively about 1/4 of this period (760 hour), the humidity exceeds 80 %.
Stored for about a week continuously under an environment with a temperature of 25 °C and a humidity of more than 80 %.

The customer really wants to know whether the above storage conditions are special or not.
Could you teach us.

Sincerely,
M. Tachibana