David,
	I found an article that should help you get started.  "Practical 
Thermal Management Issues in the Design of Power Supply Components," Power 
Conversion and Intelligent Motion (PCIM), March 1997, p. 45-57.  It addresses 
what I think you're looking for by looking at thermal resistance in the x and 
y direction of PCB and the influence of copper thickness and convective heat 
transfer.  I found their web site but was unable to find this particular 
article.  Just let me know if you need a faxed copy.

Glenn Pelkey
Quality/Reliability Engineer
Maxtek Components Corp.
(503) 627-2084

"David Taylor" <[log in to unmask]> Wrote:
| 
| 
| David,
| 
| Currently I am designing a new product which will use surface mount 
components. Some of the linear voltage regulators used in this product must 
supply a high current, and due to the large voltage 
| drop across them, it is necessary to heat sink them
| 
| We will be using the conductive surface of the PCB to provide this 
heatsinking ability. By using the specified junction-case thermal resistance 
of the voltage regulator and the specified case-ambient thermal resistance of 
the PCB copper area, we will be sure our design is robust.
| 
| Specifically, what I need to know is how to calculate the thermal resistance 
of a certain PCB copper area, which I expect will be dependant on the copper 
surface area, copper thickness, shape, whether there is solder resist placed 
over the copper surface (where the surface doesn't touch the metal of the 
voltage regulator), etc.
| 
| Any ideas as to what other specifications or reference books I can point him 
at.
| 
| 
| Regards,
| 
| David Taylor.
| Chief Engineer
| East Coast Printed Circuits
| Dee Why N.S.W. Australia.

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