BME280 showing very high humidity

[Johnvs]

We've got a number of PCBs in the production line that are showing up with high 20%+ humidity offsets.

The boards have been on a shelf at room temperature with RH betwen 40-60% for weeks before first turn on. 

1. Does the sensor need to be powered when at room temperature for 5+ days?

2. Should we follow a higher temperature reconditioning procedure - specifically which? 

[BSTRobin]

Hello Johnvs,

What software did you use?
There was BME280 example code in github, you could run it and compare your current test result.
https://github.com/BoschSensortec/BME280_driver/blob/master/README.md

[Johnvs]

Hi BSTRobin

Thank you for the link. We will certainly give this a go in parallel, but we're currently using the linux kernel driver to communicate with it.

We've not had a lot of issues until this recent batch - we have essentially manufactured these boards the same as previous batches.

I was hoping other people had similar issues with high offsets but yet managed to fix this.

The only other instance I found on the forum was this: https://community.bosch-sensortec.com/t5/MEMS-sensors-forum/BME280-Humidity-Reading-Discrepancy/td-p...

The problem is we've got one or two that are offset by +40%.

[BSTRobin · Accepted solution]

Hello Johnvs,

There was mounting recommendation in HSMI document.
https://www.bosch-sensortec.com/media/boschsensortec/downloads/handling_soldering_mounting_instructi...

Did all PCBs in the production line have high humidity offsets?

[Johnvs]

We've now tried some standard code via Arduino and get very similar results as with our software.

The variability is a bit random but we used the first re-conditioning  steps (120C, <5%rh for 2hours then 70C, 75%rh for 6 hours). This worked for us - leaving the boards at 25C for many days did nothing.

We will defininitely look into the kapton tape - not sure that was mentioned in previous versions of this document. 

One last thing to try is to put one of these boards through this reconditioning steps again, as it still has a residual offset, maybe it works or maybe we need to replace it.