Greg, every bridge diode I've had the pleasure to purchase came with instructions that it HAD to be mounted to a heat sink.
The actual area available at the base of the package is pitifully small.
As the temperature rises, the resistance goes into a run-away mode... needing to dump 6 Watts not 3.
In every power supply I've ever torn apart, every single solid state power device had a heat sink. These were typically much larger than the package.
BTW, there is a tendency to use even cheesier diodes to save on $$$. Past experience with American production may not represent current imports.
I can't even get consistency in EMT fittings... from the same supplier. (At least, that's how they were packaged.)
