Peter,
I've never seen any specific rules. There are so many kinds of LEDs, and
the power dissipation varies according to their use, like steady light
or working intermittently. Most LEDs on our products are not critical,
because of the low power dissipation, oftenly much less than 100 mW. And
LEDs are frequently mounted side by side in large arrays. Most PWBs have
mass enough to take care of that tiny power, and I have seen LED mounted
on flexes, which are not known for having good heat transportation. So,
we follow the mounting instruction that follows all LED data sheets. You
can find hundreds on the web. An exemption is certain high power IR LEDs
which need a coolant fin, but I assume you speak about the 'ordinary'
blinking ones that we see on all boards on this earth.

Ingemar Hernefjord
Ericsson Microwave Systems

-----Ursprungligt meddelande-----
Från: TechNet [mailto:[log in to unmask]] För Peter Lee
Skickat: den 28 november 2005 08:54
Till: [log in to unmask]
Ämne: [TN] Thermal Via design

Technet,

I am looking for general design guidelines on thermal vias. Can someone
please let me know if there's any reference material available?

My customer has question on ways to direct maximum heat away from the
bottom
side of SMT LEDs. The LEDs all have a 0.4" diameter base, flat on the
bottom. The PCB currently has 0.4" round pads which we paste and solder
the
LEDs directly onto.

Rgds,
Peter

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