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Date: Sun, 18 Jan 2015 13:58:27 -0500
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From: DJ Delorie <dj AT delorie DOT com>
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	from Florian Teply on Sun, 18 Jan 2015 11:04:41 +0100)
Subject: Re: [geda-user] HIDDEN PINS IN A SYMBOL
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> Slightly not directly related to symbols, but it always sstrikes me as
> odd that some (actually most for that kind of part) manufacturers
> decide to use four pins for the drain, but only one for the source
> terminal.

I always assumed the drain was on the bottom of the wafer, and that
the extra pins were for heat dissipation...  The OnSemi app note
for their ChipFET line say:

 "The pin–out is similar to the TSOP–6 configuration, with two
  additional drain pins to enhance power dissipation and thermal
  performance."

The ST smd app note says this about their SO-8 package:

 "Since the drain pins serve the additional function of providing the
  thermal connection to the package, . . ."

See also:
http://electronics.stackexchange.com/questions/32511/why-so-many-pins-for-the-mosfets-drain