15 V rail clamp in a glass MELF
The 1N4744UR-1/TR is a 15 V Zener diode in a DO-213AB MELF (glass) package, rated for 1 W continuous power dissipation. The 15 V nominal regulation point makes it a direct fit for clamping a 12 V rail or providing a local reference in a mixed-signal supply. The reflow profile follows the solder-paste recommendation for the board's pad geometry; the glass body handles the heat without cracking, but the end-cap solder joints need a consistent thermal profile to avoid tombstoning.
1 W in a small footprint — thermal reality
1 W maximum power at 25°C ambient means the junction temperature rise is limited by the board's copper area under the MELF. At 15 V and 66 mA (the 1 W corner), the glass body conducts heat to the end caps; the PCB land pattern should match the recommended pad size in the datasheet to keep the junction below 175°C. The -65°C to 175°C operating range covers military and aerospace temperature grades — the diode stays within spec from a cold-soak satellite start to an engine-bay hot spot. The glass MELF seals against moisture ingress better than a plastic SOD package, which matters for conformal-coated or high-reliability assemblies.