Dear Jimmy Blier,

I think you are looking for
     "Maximizing the Effectiveness of Your SMD Assemblies: IR Application Note
AN-994"
     http://www.irf.com/technical-info/an994/an-994.htm
It has a nice graph
     http://www.irf.com/product-info/app-dir/images/994/99405.gif
of thermal resistance (smaller is better)
vs. area of copper pad. (It specifically mentions circles, D-Pak, and SOT-89
packages,
and seems to imply that circles, squares, and typical rectangles
all act the same if they have the same area).
It also shows the affect of forced air convection.

Umm... I suspect this is HASL *without* any solder mask.





Jimmy Blier <[log in to unmask]> on 2000-09-12 04:03:18 PM

Please respond to "DesignerCouncil E-Mail Forum." <[log in to unmask]>;
      Please respond to Jimmy Blier <[log in to unmask]>

To:   [log in to unmask]
cc:    (bcc: David Cary/TULSA/BRUNSWICKOUTDOOR)

Subject:  [DC] Using PCB surface as a heatsink




Hi,

In my designs, I need to use an area of my PCB as a heat sink for various
SMD packages.
I'm looking for some technical data or formula (a calculator perhaps) that
could show me just how big an area needs to be, to adequately dissipate an
amount of power for various SMD packages or body surfaces.

Even an article on the subject would be great.

Can anyone help me?

Thanks,

Jimmy Blier
CAD Department. (Supervisor)
P A R A D O X
S E C U R I T Y        S Y S T E M S
Email: [log in to unmask] <mailto:[log in to unmask]>
Phone:  (450) 491-7444
Fax:  (450) 491-5940