HDC2010: HDC2010 failure, possible ESD issue?

Good morning, in our BLE product, schematic attached, we are using 2 HDC2010.

We are measuring air temperature outside a traveling car. Our small pcb is inside a plastic case holded by some magnets outside of the car shell.

2 out of 10 samples were not reporting correctly the temperature, reading was -40 celsius.

The 2 samples also had an anomaly in current consumption, 2mA instead of the .05mA, in stand.by (we are using a cc2640r2f as main chip).

The 2 HDC2010 are connected to the host via i2c. We use i2c also to read the battery level from the fuel gauge, battery charge reading was ok for the 2 damaged samples.

Removing one of the 2 hdc2010 from one damaged device the consumption anomaly disappeared.

So we guess the HDC2010 was damaged.

It has been damaged during while measuring, outside of the car, no manipulation, just after 15 minutes working.

Please, kindly help.

Hi Juri,

Thank you for your post and welcome to the E2E forums.

I'm still looking through your schematic, but you're correct that the 2mA current draw could be caused by some kind of device damage. It could also be caused by an assembly issue, or a small short of some kind. Is the plastic case fairly well secured, or is there a chance that condensation could be forming and causing a short?

Also, are the 2 samples you took that returned -40C the first two samples you read or are they distributed between other measurements?

If they are not occurring at startup that points to a power issue (the device is resetting between reads), which could also be due to a short of some kind. 

Best Regards,
Brandon Fisher

Hallo Brandon, 

this is Timoteo Galia, I designed the schematic and  the same company TI account with Juri.

many thanks for your feedback.

We are excluding a possible assembly issue, because the 2 units did work well at beginning.

The first unit had been working correctly for 10 hours, the second one for one hour.

It is possible that some condensation was present. But remember that even also after 2 weeks of quarantine the sensors did not work any more.

And that as I stated, removing the 2 HDC2010 from the pcb the anomaly in current consumption disappeared.

By the way, is the HDC2010 suitable for working outdoor, should'nt be because it measures humidity?

The sensor failing are 2 over 10, in the middle of the assembly sequence for these 10 samples.

We need to understand the root cause because we are going in mass production soon and we can not have such issues in production.

Thanks a lot, best regards.

Timoteo

Hi Timoteo,

Thanks for the clarifying information. 

Juri Iurato48 said:

By the way, is the HDC2010 suitable for working outdoor, should'nt be because it measures humidity?

The HDC2010 should be okay outdoors, provided that it is protected from direct condensation and mechanical damage. Do you have one of the boards that is reading 0% with the sensor still on it?

Allowing the board to just sit may not be enough to remove the moisture from the polymer. I would recommend trying a bake of that board to see if the sensor returns to normal. If the board begins reading humidity normally then the most likely culprit is condensation directly on the sensor.

Juri Iurato48 said:

The sensor failing are 2 over 10, in the middle of the assembly sequence for these 10 samples.

By "in the middle of the assembly sequence" do you mean these sensors are failing as you put your module on the car? Or are they failing before even that?

Best Regards,
Brandon Fisher

Timoteo -

You are in good hands with Brandon here - but after looking at your schematic, I would like to add that your I2C pullup resistors are too high of a value. This is probably not the issue here if they were physically damaged, but it may be part of the problem if parts are not physically damaged - what i am recommending here to you is that you lower the resistance value to make the edges of the I2C as square as possible. With nominal 100pF of bus capacitance at 400kHz, and a 10k pullup to 1.8VDC, you not only run the risk of lowering the voltage level of the signal below thresholds, it will also be very sawtooth in nature. you would be better off with 1k pullup value. At 100kHz and low bus cap, you would be OK with the 10k, (anything below 50pF) but anything above 100pF will give you similar problem as what is seen at 400kHz bus speed. 

Hallo Brandon and Josh, thanks a lot for your support.

Josh, thanks for the i2c pull-up feedback, we'll lower the resistor to 1k. 

 @Brandon:  [Do you have one of the boards that is reading 0% with the sensor still on it?]

Yes, we do have it, so will try to recover it drying first of all with air compressed gun and then baking it.

We'll try also to reproduce the issue in some other samples putting them inside water for some seconds wetting just the HDC2010 components.

i confirm that the 2 samples were working correctly for hours, working outdoors on top of their cars.

Since the HDC2010 need to work outdoor also with high humidity conditions (fog, rain) we are thinking to protect them with the Sensirion Cap SF2, as also other HDC2010 users do, according to the E2E forum.

https://www.sensirion.com/en/environmental-sensors/humidity-sensors/filter-cap-sf2/

Do you think this may help or have any other recommendation?

We are using a silicon based coating for the rest of the electronics, the DCA from Electrolube, but not for the HDC sensors, in order to have the humidity sensor working.

Thanks.

Timoteo

Hi Timoteo,

Let us know when you have the results from baking/drying. I have not used an external filter cap with the HDC2010, but if the issue you are seeing is due to condensation it may help somewhat, even with the sensing element being located on the underside of the HDC2010. 

Since you are using a conformal coating, you may want to look at the HDC2021 which includes a protective tape covering. Your coating can be applied over the device while the tape is in place, and then the tape can be removed afterwards, leaving just the sensing polymer exposed. 

Best Regards,
Brandon Fisher

Hallo Brandon,

thanks for your support.

Meanwhile the second failing unit is coming back from a customer, I have made another experiment.

I took a brand new meteotracker board, working well, I have wetted only the pcb part containing the 2 hdc2010 sensors, dipping them for a few seconds inside a glass of water.

The result is that the HDC2010 don't work any more, even the CC2640 does't boot any more correctly, the 2 sensors are probably in short circuit.

The power comsumption is also not regular, from 50uA in stand by, after the water immersion we measure in stand-by 1.7mA.

I have tried to dry and heat the sensors with hot air, with an hair phon, but it looks the HDC2010 are gone, no way to recover them.

This  means probably that the HDC2010 can not be used outdoor in rain conditions. No condensation is allowed, as expected in general for  electronics components.

We are considering to change the sensors, using a different sensor equipped with a membrane for outdoor use.

Regards.

Timoteo

Hi Josh,

thanks for your recommendations, we have some updates from the failing units from the field and the unit dipped for a few seconds inside a glass of water.

Some units were affected from the same issue described before (i2c communications with the HDC2010 failing and increased current consumprion from 50uA up to 1.7mA (in case of the dipped in water but also the others from the field had huge current consumption).

No way to recover them with compress air or heating the hdc2010 areas.

But, after 10 days, the units did work again correctly!! HDC temp and hum data OK in the I2C bus and current consumption OK, back to 50uA in stand-by.

Si we guess that the HDC2010 were ok, the problem was probably in some condensation in the bottom of the HDC2010 components.

This is a weak point of the HDC2010, in our opinion.

Condensation short circuit due probably to the very small pitch of the component.

Also as Brandon suggested we need to strength signal integrity in I2C bus reducing he pull-ups.

We have ordered some samples of HDC2021 (that unfortunately have different pin-out) to test. We'll apply conformal coating to the whole PCB area.

We'll test then the HDC2021 for outdoor harsh condition environment, since our product needs to work in rainy conditions.

Our test will be, after coating the whole board:

1-To deep for a few seconds the HDC2021 sensors in water

2-To dry them with compressed air

3- Check if they work.

Best regards.

Timoteo

Hi Josh,

we are ordering one HDC2080 evb to perform the dipping water test, after coating the board and protecting from coating the HDC2080.

Do you think it may pass the test?

In addition, can you change the title of  the article to "HDC2010, condensation issue in outdoor environment" ?

Thanks.

Timoteo