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  1. #1
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    Physical placement of MAX30205 based body temperature sensor

    Hello there,

    I'm working on a PoC prototype for a human/animal body temperature measurement system as an IoT solution. After some research, I see that the MAX30205 is an excellent choice for human body temperature measurement.

    Now I ordered the sensors alright, but I'm stuck on one question:

    How will the final sensing probe look like if I were to use this sensor? The images I see of the sensor is such that one flat side of the sensor has an "exposure pad" (EP) which should be in contact with the body. But on the same side and in the same plane, there are connection ends as well. See image below:

    Click image for larger version. 

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    Now even if I built a PCB with a connector to accommodate the sensor chip, but how could I place the EP on the body while the connector pins could also come in contact with the body and cause noise/disruption/short circuit of those connections?

    Has anybody out these built a product out of this sensor or someone has any idea how to make this work? I thought I'd connect a copper plate on the EP using a thermal connecting adhesive/tape, but I am not sure how well it will work and how much error will be introduced due to possible losses in the adhesive/tape. I also thought of soldering a piece of copper on the EP, but again not sure if I'll damage the sensor completely with so much heat being exposed to the EP.

    I hope I have explained my problem clearly enough, hope I find a decent solution.

    Regards,
    Deepak

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  2. #2
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    Re: Physical placement of MAX30205 based body temperature sensor

    Hi,

    There is nothing unusual with this package.
    Follow the PCB guidelines for this package and solder the device on the PCB.

    Klaus
    Please don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.


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    Re: Physical placement of MAX30205 based body temperature sensor

    Obviously the thermal interface will be through the PCB or an optional sensor molding. I don't think that the sensor form factor will be equally suited for all medical thermometer applications but probably for some.

    I suggest to study classical thermometer designs, determine there thermal properties (response time and error quantities) and learn how to predict it.


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  4. #4
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    Re: Physical placement of MAX30205 based body temperature sensor

    Breakout boards for this particular sensor, have a gear shaped hole under the EP pad with an extension to the centre of the hold for the ground trace (EP is supposed to be connected to GND according to the datasheet). Those breakout boards look to have some sort of thermal interface in the hole to the bottom of the PCB. One of them looks like it might use a AIN slug the other has some black substance in the hole.

    As long as you know the thermal conductivity of the various interfaces you can calculate the temperature differential between the EP and the surface of the thermal interface. That should just become an offset value (magic number).


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    Re: Physical placement of MAX30205 based body temperature sensor

    I suspect there's a thermal conductive adhesive on the Protocentral breakout board.

    I did read that the EP has to be connected to ground. That being the case, I might as well solder a metal plate EP and use that as an elevated probe and connect it to ground as well. With metal soldering, the heat transfer error should also be extremely minimal.



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  6. #6
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    Re: Physical placement of MAX30205 based body temperature sensor

    I suspect there's a thermal conductive adhesive on the Protocentral breakout board.
    The Protocentral PCB on GitHub doesn't even connect the exposed pad. I would rather refer to the Maxim eval kit PCB which uses thermal vias, a copper pour on the bottom side and thermal isolation slots. https://datasheets.maximintegrated.c...30205EVKIT.pdf



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