I've got a BME280 which has humidity values that are off by 10% or so, which from what I read happens when the operating conditions are exceeded. In this case it seems it could only be from the reflow soldering process as the boards were turned on with a few hours of soldering.
One of the 'reconditioning options' is after reflow soldering leaving the board for 5 days at >40% humidity. Is there something that would happen if the chip is powered before the 5 days has elapsed that prevents the humidity 'error' from dissapating?
I guess what I'm getting at is what are the mechanics of this? Do high temperatures reset something internally and is there some kind of internal callibration/trim that is done at the first turn on after this reset?
I am trying to avoid the situation where boards may end up in a cycle of being tested, getting baked and then sitting in a temperature and humidity controlled enclosure for hours.
First, i will say the re-conditioning is mandatory for BME280 after SMT process, otherwise it will have deviation of humidity output.
If you follow the condition given in our HSMI document, you should good for this process.
But i don't think the power on sensor during the period will affect the re-conditioning result. The re-conditioning is more for the MEMS unit of humidity inside sensor. It isn't matter to the internal "calibration". The trimming value got in component level in factory is not changing in SMT and re-conditioning stage.
Static factory trimming is what I would have expected. We would be using this sensor in indoor environments which should be between 40-60% humidity and our office temperature is around 22-23C. With this similarity to the third reconditioning option (post reflow) I would have expected the offset to still reduce over time even if slightly slower. Is the process sensitive enough that it must go straight from the oven to a 25C 40%+ environment? And that if the temperature is less than 25C the effectiveness of the reconditioning drops off a cliff?
There are three methods provided for reconditioning.
You can choose one of them. for example if oven is not used, you can put the device into room temperature with >40% relative humidity for more than 5 days.
With Oven will speed up the reconditioning.
For reconditioning, the room temperature (25 degrees) are lowest temperature required for this process.