30 ns reverse recovery — what it buys you
The STTH4R02FP is a fast-recovery epitaxial diode with a reverse recovery time (trr) of 30 ns. That places it in the ultrafast class — fast enough for 100 kHz+ switching in a boost PFC stage or a flyback snubber, where a standard recovery diode would overheat from reverse-recovery losses. The 200 V reverse voltage and 4 A average forward current suit it for secondary-side rectification in offline power supplies up to a few hundred watts, or as a freewheeling diode across a relay or inductive load. Forward voltage drop is 1.05 V at 4 A, which is typical for a 200 V ultrafast in this current class. The 3 µA reverse leakage at 200 V is low enough that it won't affect efficiency in most designs, but worth noting if the diode sits across a high-impedance node in a hold-up circuit.
TO-220 Full Pack — isolated tab matters
The STTH4R02FP comes in a TO-220-2 Full Pack, also called TO-220FPAC. The key difference from a standard TO-220 is that the metal tab is fully encapsulated in plastic — electrically isolated. The trade-off is slightly higher thermal resistance junction-to-case compared to a standard TO-220, so the heatsink needs to be sized with that in mind. Mounting is through-hole, so it's a hand-solder or wave-solder part.