HDC3021: Out of Calibration, start from our stock,

HDC3021 Out of Spec.xlsx Spread sheet of table above.

Oh yes, The Michell OptiCal was checked against a calibrated Rotronic HCS2 sensor and differences were < 0.2%. HDC3021s were sent to external calibration house, and they also got similar results to the original as found values, before the reconditioning.

Hi Nick,

Thank you for the detailed measurement report. During the 6 months in stock, how are the HDC3021's stored? What ambient temperatures and humidity are the parts stored at? Are the sensors stored in any pink anti-static material or any LDPE bags? Storing HDC3021 improperly, even with the tape on, can cause the temporary positive RH offsets you are seeing.

Thank you.

-Alex Thompson

Hi Alex.

They are stored between 18 - 28 degC and 25 to 60% RH.

I've attached the datasheet for the bags we use to store them.

Static Shielding Bag.pdf

Hi Alex.

Also, this is not an offset problem. this is a gain issue. 

You will see above, the span improves after the re-conditioning of the sensor.

I've worked with Humidity Sensors since the early 1990s, calibrating with Saturated Salts to using the Automatic OptiCal Calibrators.

We don't use any of the pink/blue or yellow bags anywhere. and we also don't use the pink bubble wrap on external packing.

The Kapton protection, what protection does the Kapton tape give. Only against the soldering processes?

Regards

Nick

Other manufacturers list compatible bags. What do TI use?

https://stroebel.de/en/bags-pouches/esd-protection/esd-shielding.html

Nick,

The Kapton tape cover will mostly just protect against the soldering process. While it will slow down gasses and humid air from getting to the sensor cavity, those will eventually penetrate (for example, RH response time will go from a few seconds with the tape off to a few hours with the tape on).

Do you think there is any chance that the HDC3021s were exposed to any potential chemical contaminations during storage and handling? Were the devices tested with the kapton tape on at any of these readpoints? A negative gain shift like this usually indicates some chemical contamination has occured, and baking can often resolve that effect.

The storage bags you are using look good. 

Thanks

-Alex

thanks for the reply Alex.

I agree with you that it looks like some kind of contamination, but I don't know where it came from.

We currently have two product assemblies in stock. 

One assembly has around 1600pcs, and another 1000pcs waiting to be shipped to us.

For the second assembly, we have around 200 pcs in stock.

Both were built at different times, with subcontractors, and in different parts of the world.

All our subcontractors use no-clean lead-free solders and do not wash (clean) the boards post-assembly.

Currently, we are  Re-conditioning small amounts of stock. We don't want to bulk re-condition until we understand what is causing the effect. Otherwise, we might have to repeat it again later.

I think the response time through the Kapton will be very slow. We normally use two layers of PTFE tape as a filter on some products and this slows the response significantly.

Is there a test I can perform on the units with the Kapton still fitted?

Do you want samples to test a TI?

The only comment I have is, that when we received the items, full calibration was undertaken on a number of devices, and all passes. They have been in our stock for approx 6 months, and now they don't. 

Below is a product with the HDC3021 which was shipped to a customer in April 2024, the stock had only arrived weeks earlier. The humidity was very accurate without any adjustments.

Hi Alex.

I'm out of the office tomorrow, back on Monday 11th Nov,

NIck,

If you could provide the MSDS (material safety datasheet) for the storage bags that could help indicate a possible contaminant. Is there any chance that during the removal of the Kapton tape for the post 6-months test, there were any chemicals outgassing nearby?

Please also take some pictures of the sensor cavity under a microscope, to look for any signs of material contamination. 

-Alex Thompson

Hi Alex.

I have requested the MSDS sheet from the supplier. 

One of our sub-assemblies has to be soldered, which is for attaching a battery, and the Kapton is removed afterwards.

The other is a plugin board, and there is no soldering. 

There is no cleaning of the boards in production. 

I cannot think of any contaminants.

yes, I will take photo's of cavity tomorrow.

Regards

Nick

HDC3021 stock.pdf

I have taken images of the two different sub-assemblies we use. Both stocked with the Kapton fitted until until we calibrate.

Still waiting for the supplier to give the MSDS sheet for the bags. 

Hi Nick,

Thanks for looking into potential contamination sources so thoroughly. Were the sensors exposed to light while they were stored, like on shelf perhaps, or even near a window. i wonder if they could have been getting continuous UV light exposure. Or were they kept away from light, like in a cabinet?

Regards

-Alex Thompson

Hi Alex.

Our stock room has no windows and only a roller door at one end. The door is closed 99% of the time. and no stock is within 5 metres of the roller door.

No, we don't use any cabinets. We use stock boxes as shown below or cardboard boxes. But they are always sealed inside the ESD bags

Still waiting for supplier to give me MSDS sheet for ESD bags.

How did the sensors look to you?  they looked ok to me, apart from the excess backing for the kapton. The kapton backing is silicone based I guess, so it will not attack the season. The only downside with silicone is it adsorbs humidity.

Also found this in the forum.

https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/1200697/hdc3021-hdc3021

Nick,

The sensors storage looks good to me, it's not obvious to me where the source of contamination is occurring, but since reconditioning resolves the issue, that may be your only option. 

Regards

-Alex Thompson

Hi Alex.

It's not the answer I wanted, but it's not an ideal world. haha

Previously I reconditioned with the Kapton tape off, is it possible to recondition with it still on?

Cheers

Nick