TMP117: Why does TMP117 recommend not soldering the thermal pad?

Dear Koba - 

Thanks for the post. Soldering the pad on a part like this is generally what is done and this is a good question.

The reason we have the recommendation is to explain how to exactly match the performance of the datasheet specifications. Please understand here that the TMP117 is a high precision sensor, a leader of just a handful of components available like this in the market - as such, in order to support the device completely, our team members took some effort to characterize the performance of that package version, with and without the pad soldered.

Against an even higher precision temperature sensor being use as a reference, the TMP117 did fantastic either way, but technically it performs best without having the pad soldered. You can solder the pad, but you will see some small mC offset from doing it, if you are attempting to measure ambient temperature. I hope this is a direct enough explanation. 

Thanks!