SOT-23-3 PCB Footprint: Dimensions, DFM, and Assembly Guide

SOT-23-3 is a gull wing package used for surface mount assembly, also seen labeled TO-236AB, SOT-23, SC-59 family. A dependable footprint follows the exact orderable-device drawing rather than the family name: nominal body About 2.9 × 1.3 mm nominal, overall span About 2.8–3.0 mm across the leads, seated height Typically 0.9–1.2 mm, pitch 0.95 mm between the two same-side leads, pin count 3, and exposed pad None.

Use the package drawing for the selected MPN and verify the symbol-to-pad mapping independently.

Typical uses include small transistors, diodes, references and regulators. TO-236/SOT-23 dimensions have variants; the exact manufacturer's package drawing and pin table control.

• The body and lead span are broadly standardized, but SOT-23 is a mechanical package, not a pinout standard.
• Pin 1 is normally identified by drawing convention rather than a prominent molded mark, so assembly documentation matters.

Keep sensitive base, gate, or feedback nodes short and separate from switching copper according to the circuit function.

• For regulators or transistors dissipating power, use the datasheet's copper assumptions; three narrow leads provide limited heat flow.

Hand assembly is rated easy. Fine hoof tip with flux or ordinary stencil reflow. Watch for pinout swaps among transistor, diode, and regulator variants.

• Maintain visible toe fillets without extending pads so far that the package can float during reflow.
• Keep silkscreen polarity or pin-one marks outside the courtyard and unambiguous after placement.
• Validate alternate MPNs because the same outline can carry incompatible pin assignments.

Inspection focus:

• All three gull-wing joints are optically accessible; inspect heel and toe wetting and component rotation.
• Functional test must catch a mechanically correct but electrically incompatible substitute.

Common mistakes:

• Assuming every SOT-23 transistor uses gate/base on pin 1 and a common drain/collector mapping.
• Letting the autorouter lengthen a sensitive feedback or gate loop because the package is small.

1. Before approving SOT-23-3, compare the exact orderable-device drawing with the library item: body range (About 2.9 × 1.3 mm nominal), terminal or lead span (About 2.8–3.0 mm across the leads), pitch (0.95 mm between the two same-side leads), pin count (3), height (Typically 0.9–1.2 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 pinout swaps among transistor, diode, and regulator variants with the assembler, confirm that fine hoof tip with flux or ordinary 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. The dominant SOT-23 risk is a plausible-looking but wrong pad-to-pin mapping.
2. S2Solder-mask web and pad opening. The 0.95 mm lead pitch still needs a manufacturable mask dam.
3. S2Courtyard and body clearance. Neighboring passives must not block visual inspection of the three leads.