The 1N6624US is a Microchip Technology fast recovery rectifier diode rated for 990 V DC reverse voltage and 1 A average rectified current, with a forward voltage of 1.55 V at 1 A. The 500 nA reverse leakage at 990 V is tight for a 1 A diode at this voltage class — it tells you the die has clean passivation and the junction holds off the field without micro-plasma leakage paths.
The SQ-MELF A package (also called A-MELF) is a surface-mount cylindrical body with metallized end caps — it reflows like a standard SMD but the cylindrical shape means the solder fillet wets around the entire end cap, giving a stronger joint than a flat SOD-123 in high-vibration environments. The 10 pF junction capacitance at 10 V is low enough that the diode does not load the switching node with extra charge storage.
Microchip lists the 1N6624US as Active.