different mosfet package of same rating

[electros6]

Hi guys,
         while searching for a mosfet I noticed that STP9NK90Z and STW10NK80Z  has same voltage and power dissipation, but the former is in TO-220 package and later is in TO-247. Both have same rating what make them to choose different package what are the factors affect this parameters.       
   

[David_AVD]

Maybe the larger package has a better heat transfer (to heatsink) rating?

[T3sl4co1l]

Semiconductor ratings are with the device in a bath of boiling freon.  When they say "case temperature 25C", they don't mean "hook it up to a block of copper at 25C", they mean all exposed points on the case surface are 25.00C!

Since most of the heat goes out the metal plate under the chip, the ratings are very similar between DPAK, D2PAK, TO-220 and TO-247 devices, being limited by plate thickness and die size.

Moral of the story: the power dissipation rating has absolutely nothing to do with how much you can dissipate in a typical heatsink assembly.  There is no substitute for a good thermal design.

Tim