Carefully crack open a device and look at the construction.
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The drain lead is part of the lead frame to which the die s bonded.
Memory says the back of that leadframe is the flat side of the device.??
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The gate and source are via bond wires to the die.? Hence there
is less heat transfer to the leads.
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The ideal device is one where the drain is bonded to an accessible tab?
for example VN7000 (to92 with tab out the top) and the IRF510.
In both cases the direct mechanical (or solder) contact has greatly
increased heat transfer.?
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The yabut of it all is the source lead carries the most current and
the wire bond to the lead is the limiting factor.? ? Enough current
and the that fine wire vaporizes.? ? Its one of the things that limits?
power handling of the device.??
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--
Allison
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direct email will go to a bit bucket.
