Power Packages Not on a Heatsink Free Standing

Power packages not mounted on a suitable heatsink can expect to dissipate less than five percent of the maximum specified power capability of the package. So 100 W devices will only dissipate 1 to 2W when they are free standing. This also includes using the PC board copper plating as a heatsink. Thus, great discretion should be used when cost is the most important issue. 

As one can see by the typical values of the junction-to-air thermal resistance, it doesn t require much power to result in very high junction temperatures. If the designer can possible mount the power package on any metal surface to increase the radiating surface area, it will only improve the junction temperature. 

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