SOT-89-3 PCB Footprint: Dimensions, Thermal DFM, Assembly

SOT-89-3 is a power package package used for surface mount assembly, also seen labeled TO-243AA, SOT-89, UPAK variants. A dependable footprint follows the exact orderable-device drawing rather than the family name: nominal body About 4.5 × 2.5 mm, overall span About 4.5 × 4.0 mm including leads/tab, seated height Typically 1.5–1.7 mm, pitch About 1.5 mm, pin count 3; center lead usually shares the broad tab, and exposed pad Broad center/tab terminal.

Use the exact package drawing; UPAK and manufacturer-specific SOT-89 variants can alter lead geometry.

Typical uses include small linear regulators, RF transistors, medium-power discretes. SOT-89/TO-243 outlines have supplier variants; exact lead and tab dimensions come from the orderable part drawing.

• The center connection widens into a tab under the body, providing more copper contact than SOT-23 but less accessible wetting than SOT-223.
• Pin sequences vary by regulator and transistor; the mechanical outline supplies no functional convention.

Spread copper from the center tab on the correct net, preserving clearance from the two outer leads and any sensitive input trace.

• For RF devices, follow the manufacturer's evaluation layout because added thermal copper also changes parasitics.

Hand assembly is rated moderate. Preheat and use a hoof tip or reflow so the broad center tab wets fully. Watch for bridging the close leads and leaving the heat-spreading tab under-soldered.

• Keep a defined mask dam between the wide center land and outer lead pads.
• Balance paste so the body does not tip onto the central solder volume.
• Check whether the tab is inspectable from the package edge with the chosen land extension.

Inspection focus:

• Inspect the two outer leads and exposed edge of the center joint; use thermal testing to reveal a weak tab connection.
• Verify the part marking against the exact BOM because incompatible regulators can share the outline.

Common mistakes:

• Reusing a footprint whose center land is too narrow for the selected manufacturer's tab.
• Treating extra copper as free cooling on an RF node without checking its electrical effect.

1. Before approving SOT-89-3, compare the exact orderable-device drawing with the library item: body range (About 4.5 × 2.5 mm), terminal or lead span (About 4.5 × 4.0 mm including leads/tab), pitch (About 1.5 mm), pin count (3; center lead usually shares the broad tab), height (Typically 1.5–1.7 mm), and exposed-pad definition (Broad center/tab terminal). Record the source drawing revision and every intentional courtyard, toe, heel, side, mask, or paste adjustment.
2. Treat the moderate hand-solder rating as a prototype-planning input, not proof of production yield. Review bridging the close leads and leaving the heat-spreading tab under-soldered with the assembler, confirm that preheat and use a hoof tip or reflow so the broad center tab wets fully 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. Center-tab identity and the two outer pins vary by device.
2. S2Solder-mask web and pad opening. Narrow gaps beside the tab need a manufacturable mask web.
3. S2Courtyard and body clearance. Thermal copper and rework access must fit around the compact package.