I'm try calculate a heat emission for rectifiers couple (suppy for audio power amp.), and use PCB as a heatsink (without additional metal sinks - don't ask me why), but can't find - how calculate sufficient ground foil pad. Incoming data:
From transformer- 45V AC, double Shottky diode in bridge (MBR2080 in 3 cases TO-220), average current- 3A (in peak - 5A). Most hardly power (and termal) conditions for "positive" part of bridge (case with common cathode is in constant load). Power dissipation on this body is (0,8V×3A) =2,4W - allowable. Thermal impedance body/ambient for TO-220 is around 50 C°/W. In fact I get rising temp up to 120 C° + ambient 25 C° = 145C. Too much...
If I place TO-220 (using screw) on bridge PCB, with appropriate area of foil pad - thermal impedance will lower, and temp will decrease.
OK, well, fine, (applauses), "smart guy", etc... But, on this moment I'm download long megabytes of tech.datas & datasheets concerning this question, even math modeling. Nowhere answer... In this galaxy possess any computation formula or not?
Tearfully ask: how (where) I did calculate demand area of two-layer PCB?!