SOD-523 PCB Footprint: Dimensions, Polarity, and DFM Guide

SOD-523 is a chip component package used for surface mount assembly, also seen labeled SC-79, small-outline diode 523, SOD523. A dependable footprint follows the exact orderable-device drawing rather than the family name: nominal body About 1.6 × 0.8 mm, overall span Typically 1.5–1.7 mm long, seated height Often 0.6–0.8 mm, pitch Two end terminals; no lead pitch, pin count 2, polarized, and exposed pad None.

Use the exact SC-79/SOD-523 drawing and manufacturer land pattern; do not reuse 0402 passive lands.

Typical uses include ESD steering, compact signal clamping, wearable protection. SOD-523/SC-79 is a compact package family; use the exact MPN drawing for lands and marking convention.

• The body is similar in length to an 0603 passive but uses polarized diode terminations and a device marking that may be nearly invisible after placement.
• A two-terminal size code describes an envelope, not universal termination length, height, polarity, power, or voltage capability.

Place the device immediately at the protected pin, keep the return short, and balance the two pad thermal connections.

• 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 hard. Precision stencil and reflow; microscope/hot air for rework. Watch for unreadable polarity, part loss, and tombstoning on asymmetric copper.

• Verify placement-machine and AOI capability, stencil aperture registration, and a polarity mark outside the tiny body courtyard.
• 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:

• Use magnification plus electrical polarity testing; ordinary visual inspection may not resolve the molded cathode mark reliably.
• 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:

• Treating SOD-523 as a polarized 0603 passive produces unsuitable pads and can reverse the diode in assembly data.
• Do not substitute a resistor, capacitor, LED, fuse, ferrite, or shunt solely because its nominal body code matches.

1. Before approving SOD-523, compare the exact orderable-device drawing with the library item: body range (About 1.6 × 0.8 mm), terminal or lead span (Typically 1.5–1.7 mm long), pitch (Two end terminals; no lead pitch), pin count (2, polarized), height (Often 0.6–0.8 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 hard hand-solder rating as a prototype-planning input, not proof of production yield. Review unreadable polarity, part loss, and tombstoning on asymmetric copper with the assembler, confirm that precision stencil and reflow; microscope/hot air for rework 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. Polarity, exact land pattern, paste balance, fab mask capability, and protection-loop placement are all gate 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.