SOD-123 PCB Footprint: Dimensions, Polarity, and DFM Guide

SOD-123 is a chip component package used for surface mount assembly, also seen labeled small-outline diode 123, SOD123. A dependable footprint follows the exact orderable-device drawing rather than the family name: nominal body About 3.7 × 1.8 mm, overall span Typically 3.5–3.9 mm including terminations, seated height Often 1.0–1.35 mm, pitch Two end terminals; no lead pitch, pin count 2, polarized, and exposed pad None.

Use the exact SOD-123 variant and manufacturer pad recommendation; flat-lead and molded-terminal details vary.

Typical uses include signal diodes, small TVS devices, Schottky rectifiers. SOD-123 describes a family; exact terminal dimensions and land pattern come from the chosen diode drawing.

• SOD-123 is smaller and lower-power than SMA, yet larger and easier to hand assemble than SOD-323 or SOD-523.
• A two-terminal size code describes an envelope, not universal termination length, height, polarity, power, or voltage capability.

Place protection diodes beside the protected connector and route surge current directly; keep the cathode mark visible after assembly.

• Keep copper and thermal mass reasonably balanced at both ends, and move vias outside the paste-bearing land unless the assembly process is designed for via-in-pad.

Hand assembly is rated easy. Fine-tip hand solder or stencil reflow. Watch for reversed cathode, sma/sod footprint confusion, and thermally unequal pads.

• Balance paste and copper, preserve an unmistakable polarity mark, and confirm component height under shields.
• Select the stencil aperture with the assembler; copper, mask, and paste openings solve different process problems.
• Keep brittle ceramic bodies away from panel break lines, mounting hardware, and enclosure features that bend the finished PCB.

Inspection focus:

• Inspect both end joints and cathode orientation, then electrically verify forward drop, clamp direction, or rectifier behavior.
• Compare the two visible end fillets for wetting, skew, and solder volume, then use electrical test for failures such as cracked ceramics that AOI cannot see.

Common mistakes:

• Using the schematic diode symbol direction as the only polarity cue leaves assembly operators and AOI without a physical cathode reference.
• Do not substitute a resistor, capacitor, LED, fuse, ferrite, or shunt solely because its nominal body code matches.

1. Before approving SOD-123, compare the exact orderable-device drawing with the library item: body range (About 3.7 × 1.8 mm), terminal or lead span (Typically 3.5–3.9 mm including terminations), pitch (Two end terminals; no lead pitch), pin count (2, polarized), height (Often 1.0–1.35 mm), and exposed-pad definition (None). Record the source drawing revision and every intentional courtyard, toe, heel, side, mask, or paste adjustment.
2. Treat the easy hand-solder rating as a prototype-planning input, not proof of production yield. Review reversed cathode, sma/sod footprint confusion, and thermally unequal pads with the assembler, confirm that fine-tip hand solder or stencil reflow is compatible with the build, and require the S1 connectivity gate plus relevant S2 geometry checks to pass against the released footprint and selected fabrication profile.

Manufacturing gate checks:

1. S1Pad count, numbering, and schematic parity. Two-pad polarity, package variant, protection-loop routing, mask geometry, and BOM-to-footprint mapping need checks.
2. S2Solder-mask web and paste geometry. Two close lands still need a process-capable mask dam and a paste plan that will not tombstone the body.
3. S2Courtyard and body clearance. The body, leads, placement tolerance, rework access, and nearby height limits all belong in the manufacturing review.