We reference this heat sink temperature calculator webpage in several Adafruit product descriptions and Learning System guides, but it’s always a good reminder here on the blog too, and it’s worthy of keeping in your bookmarks for quickly locating in the future.
Power components have a maximum junction temperature, which must not be exceeded to prevent damage to the device. Devices are encapsulated in packages which have different levels of thermal resistance. When designing power electronics, the heat dissipation of the device, coupled with any heat sinks, as well as the maximum power dissipated by the device, must be analyzed to insure that the device operates within allowable specified limits.
This calculator and tutorial computes the junction temperature of a power electronics device given the maximum ambient temperature, and the heat sink thermal resistance. The calculator will let you know if the maximum junction temperature could be exceeded for a given power, and likewise will tell you the maximum power that the device can handle for a given maximum power.