I have a comment also.  This is often done but I don't have any
calculations to back up the practice.  It seems to me that this
surface, whether 1 oz or 2 oz or whatever, is a black body radiator
and that is what is "cooling" the heatsink tab on the regulator.  It
isn't convective cooling so putting holes in the plane makes matters
worse as you have reduced the surface area of the radiator.  The
surrounding enclosure and other parts are at a LOWER black body
temperature, presumably, than the heatsink tab and the plane (assuming
a good thermal contact between tab and plane using thermal grease or a
SIL pad) so would absorb heat and lower the plane temp.

Doug Brooks: what do you think is the predominate effect?

Regards,

Bob Landman
H&L Instruments


----- Original Message -----
From: Abd ul-Rahman Lomax <[log in to unmask]>
To: <[log in to unmask]>
Sent: November 15, 1999 2:21 PM
Subject: Re: [DC] Calculating thermal dissipation of external plane
heat sink area


: At 11:04 AM 11/15/99 -0500, Greg Bordash wrote:
: >We are in the process of using an external (Primary or Secondary)
layer heat
: >sink plane for a regulator type device on a multi layer design and
require a
: >means of calculating the required area based on its power
requirements.
:
: Just a suggestion: if a heat sink plane has many large open
plated-through
: holes in it, it can be *much* more effective, probably due to
increased
: surface area as well as convective cooling due to air flow through
the holes.
:
: [log in to unmask]
: Abdulrahman Lomax
: P.O. Box 690
: El Verano, CA 95433
: