The STTH3L06B is listed as obsolete. For a repair bench or a production line that needs this exact diode, the only path is the surplus and broker market — which is where this listing comes in.
85 ns reverse recovery — the switching edge
That 85 ns trr is the spec that matters for a boost PFC stage or a flyback snubber — it tells you how quickly the diode turns off, which directly sets the switching loss and the snubber component values. At 3 A forward current and 600 V blocking, this diode fits the output rectifier slot in a 150–300 W offline converter, or the boost diode in a power-factor-correction stage running at 50–100 kHz.
Forward drop and leakage — the thermal budget
Maximum forward voltage is 1.3 V at 3 A, and reverse leakage is 3 µA at 600 V. The 1.3 V Vf means about 3.9 W peak dissipation at full rated current — that's manageable in the DPAK package with the tab soldered to a decent copper area, but you'll want to check the junction temperature. The junction is rated to 175 °C maximum, so there's headroom, but the thermal resistance from junction to ambient in a DPAK without a heatsink is around 80–100 °C/W, which limits continuous current to maybe 1.5–2 A in still air. If your design runs the diode hard, plan for the tab to carry the heat out through the PCB.
DPAK footprint — layout gotcha
The package is a standard TO-252-3 DPAK — the tab is the cathode. No insulator pad; the thermal vias go straight to the cathode plane. If you're swapping this onto a board that originally had a different diode, check the pinout — the STTH3L06B is a standard diode, not a Schottky, so the cathode is the tab and the middle pin, anode is pin 1.