I need help =(

[Tom F]

If i had a choice i'd run stuff at a max of about 60C, but it costs too much for manufacturers to bother. It's cheaper to deal with a few failures than to put a $1 heatsink on something that will be sold by the thousand or even the million.

To keep say 12 transistors running at about 40F over ambient, if there was a total dissipation of 240W, you would need a heatsink with a thermal resistance of 0.1c/w temperature rise. Passive cooling of that efficiency is amazingly expensive (a sink that big would be enourmous)

They have to have high heat tollerances, because in an application such as a small mobile device that has to handle a lot of current (such as a brushless ESC), yet be compact and lightweight, it's not always possible to keep it small and also running cool. The total thermal resistance of a sink on a brushless controller might be 2c/w if you were lucky, so if you dissipate 40W on it, it will be 80C over ambient!

[BrianG]

I agree, and that's why all my power projects are huge and clunky from heavy duty heatsinks and/or fans. After running my Quark 125B for a while it got too hot for my taste, so I thermal epoxied (Arctic Silver) a secondary heatsink. It doesn't look good, but lowers the temps to more reasonable levels (to me).