This question is related to who knows how to design a thermal management. I started learn to do this, at hobbyst level.
So, this is the assumption of the situation: When someone design the thermal handling of an electronic component (let's say an average IC), briefly its starts from the max junction temperature and goes up to the ambient removing the kept heat from the initial temperature, due to the thermal resistance. Eventually, in order to achieve compatibility with a given ambient temperature, with an equation can devise the thermal resistance of the heatsink.
For example, Tj=130°C, Ta=30°C, P = 2.3W and the various thermal resistances from junction to ambien WITHOUT the heatsink one are in total 17°C/W. At 30°C of Ta, I need an heatsink of ((Tj-Ta)/P)-17°C/W = 26.5°C/W.
Now, I need few clarifications (assuming what I said unitl now is roughly correct...).
Clarification 1: this design will not allow the system to be used in ambient which is higher than 30°C (using only convection). Correct?
Clarification 2: the temperature of the surface of heatsink should be higher than 30°C? Measurements were indicating an heatsink temperature higher than 45°C at Ta = 20°C, so I'm supposing the answer is yes. But how to calculate them a priori, to make the proper controls?