MOSFET SO8-FL package app note from ON Semiconductors provide same thermal performance as metal top package with heat sink attached. Link here (PDF)
The SO8−FL package can deliver high power density and provides excellent thermal dissipation to create a high efficiency, cool design environment when properly cooled. Metal−top devices attempt to remove heat easier through direct contact to the source. This application note provides a comparison of an SO8−FL device with a metal top device of comparable die parameters, and will show that the SO8−FL and metal top devices have comparable thermal performance. Furthermore, it will be shown that while the package itself influences thermal performance, the use of a heat sink provides the largest improvement to thermal dissipation, regardless of package.
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