What the 90 ns trr means at 1000 V and 12 A
That trr figure puts it in the ultrafast class for a 1000 V part — it recovers fast enough for hard-switched power converters running at 50–100 kHz, where a slower diode would burn through switching loss and overheat the junction. The forward voltage drop is 2 V at the full 12 A rated current, which is typical for a high-voltage fast diode of this current class. The 10 µA reverse leakage at 1000 V is tight enough to keep standby dissipation under control in offline power supplies.
It comes in a D2PAK (TO-263-3) surface-mount package. The large tab is the cathode and carries the heat — the board needs a decent copper pour on the drain pad to pull the 12 A continuous. From a rework standpoint, D2PAK is one of the easier high-power SMD packages to work with: the tab is exposed, you can hit it with hot air from the bottom side if the board has a thermal via array, and the three leads are widely spaced so bridging is unlikely. Just watch the bake requirement if the reel has been open — D2PAK can trap moisture under the tab.
Where this diode fits
A 1000 V, 12 A fast recovery diode with 90 ns trr is a natural fit for the output rectification stage of a power-factor-correction boost converter, or as the boost diode in a two-switch forward or LLC resonant converter. It is also a candidate for freewheeling diodes in motor-drive applications where the bus voltage reaches 400–600 VDC and the switching frequency is in the tens of kilohertz.