Author Topic: Si7021: with or without the cover?  (Read 1487 times)

WhiteHare

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Si7021: with or without the cover?
« on: February 26, 2016, 09:43:05 AM »
I notice there are different models, and some come with the cover and others don't.  Apparently the cover helps to keep dust and other contaminants off the sensor element.  I'm leaning toward getting one with the cover to try.  Aside from incremental cost, any reason not to prefer one with the cover?  I'm not sure why ones without the cover are even sold.

jra

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Re: Si7021: with or without the cover?
« Reply #1 on: February 26, 2016, 10:31:06 AM »
My read of the Si7021 data sheet indicates that the cover servers two purposes:
  • Protects the device during PCB assembly by keeping flux residue and solder droplets off the sensor
  • Protects the device from liquid, dust, etc. during use.
TI's data sheet for the pin (not software) compatible HDC1080 says:
Quote
9.3.1 Soldering
When soldering the HDC1080 use the standard soldering profile IPC/JEDEC J-STD-020 with peak temperatures
of 260 C.
When soldering the HDC1080 it is mandatory to use no-clean solder paste and no board wash should be
applied. The HDC1080 should be limited to a single IR reflow and no rework is recommended.
9.3.2 Chemical Exposure and Sensor Protection
The humidity sensor is not a standard IC and therefore should not be exposed to particulates or volatile
chemicals such as solvents or other organic compounds. If any type of protective coating must be applied to the
circuit board, the sensor must be protected during the coating process.
TI doesn't offer a factory installed cover as an option.  If you use any of these sensors outside, you will want to protect the sensor and PCB if from the elements anyway and I wouldn't rely on just the cover for that.  My impression is that for hobby use it probably doesn't make much of a difference whether you order it with or without the cover as long as you mount it in some sort of enclosure.  My Weathershield is at home so I can't currently take a look and see which version Felix sells.  The picture in the store looks like they have covers.

Felix

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Re: Si7021: with or without the cover?
« Reply #2 on: February 26, 2016, 10:57:11 AM »
Some users reported that the filter might influence the readings. In my use I have not really noticed this but I use them without the cover.
Also my latest batches of sensors were without covers, I did not see any issues during assembly.
I do the assembly on a pick and place, not by hand, and reflow in a reflow conveyor oven so other than me moving the panels from one machine to the other, the process is pretty controlled.
There should be no residue or solder flying around during assembly or reflow.