Could you please expound on the recommended use of the thermal pad used in most of your TMP local temp sensors (for instance TMP117). I am looking to measure the temperature of a solid surface. The datasheet seems to suggest measuring through the PCB, but aren't FR4 and solder mask poor thermal conductors?
There is also mention of a copper plane on the bottom of the board. Since FR4 is a poor thermal conductor, should the copper plane be connected to the exposed pad with thermal vias to help conduct the heat through the PCB to the exposed pad? Should the solder mask be removed from that copper plane so it is in more direct contact with the surface being measured?
Ideally the sensor and its PCB would be upside-down on my solid surface so that only the top of the sensor is touching my solid surface and so the PCB doesn't effect the surface's temperature gradient. Is that better or worse than sensing through FR4?
Any other advice you could offer is greatly appreciated.
Thank you,
Garrett