I am an EE that is fresh out of college and and starting at a smaller company, and I have a question about electronic self heating, and how to keep heat from spreading in a PCB to heat sensitive components, such as thermistors that are being used to measure ambient temperature, currently there is issues in a few designs, where the temperature inside the housing increases by half a degree C with traces run directly to the thermistor without thermal reliefs or and care to trace size. The devices I have seen having trouble are usually attempting to read ambient temperature at .25% accuracy between the ranges of -20 to 85c (currently done on some designs by having two separate boards in the enclosure with small wires run between the two)
The "hot" components are mainly the switching supply, and the MCU, in most cases for some designs I am looking at, they run at 10-20 mW, and the PCB size would generally be around 2in x 4in.
Would it be better to run large ground planes underneath these components to try and dissipate the heat on that side of the board? Or would the heat just transfer to the pcb's dielectric and heat up the thermistor that way?
Also, would it be better to run thinner traces with thermal reliefs to the thermistor to cut back on heat transfer through the traces, or would it be better to run wider traces to try and dissipate heat before getting to the thermistor?
The common value of thermistor I am looking at is a 10k-2 NTC.