Hi, I don't have any hard numbers for heat dissipation for you, but I hope this helps. I've done this a number of times at different companys and it seems to work. Provide a solid copper area as big as possible under the component to be heatsinked on the external layers. Remove solder mask where ever the component touches the heatsinked plane. If possible duplicate this plane on all layers. Stitch the multiple planes together with vias, (I've used .023 dia and .033 dia with equal success). Put the vias on a .100" staggered grid if possible. (tip of the hat to Ralph Hersey here). x x x x= via hole - x x x | .10 x x x | | - x | x x | | -| |-.050" If possible make via connections to the planes solid ie. no thermals. If you are using forced air cooling you might use a few larger holes to allow air circulation. Best of luck, Rob ROBERT BUTTERWORTH ADC VIDEO SYSTEMS WALLINGFORD, CT 06492 [log in to unmask] *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************