Hi,
However no information is provided on “desirable” temp, per my original question.
Is your indirection out of frustration... my apologies if this gets asked frequently.
No. No frustration. It was meant seriously.
We do have less information than you. The datasheet is one of the most reliable sources of information.
But I agree "desirable" is not written in the datasheet.
So my opinion on that:
At first I wanted to answer "as low as possible"(usually below 50°C), because I am a designer for "long life" industrial electronics. (Someties for clean room environment)
I've seen resistors that were specified for temperatures > 120°C. They probably never were >60°C but the PCB they were monted on looked like it was burnt with >300°C.
The problem is "time" (besides of PCB material). The resistor was "warm" 24/7 over ten years.
So if reliable long life is "desirable" on a continously hot resistor, then low temperature is desirable.
But also low cost may be desirable, short life time (planned obsolescence), heating of a PCB that is operated in cold environment, small size, or when the resistor is hot just for seconds a day...
I've seen sensors using hot resistors as inert gas sensor or as gas flow sensor..
So for most designers "<50°C" is not desirable.
Klaus