1.25mm 9-Pin PCB Header: Complete Datasheet & Pinout

1 February 2026 32

A 1.25mm 9-pin PCB header packs nine signal contacts into roughly 11.25 mm of board space (1.25 mm pitch × 9). This guide provides a datasheet-style breakdown, exact pinout guidance, footprint, and layout tips for US-market hardware engineers and PCB designers.

Quick Overview & Typical Use Cases

What is a 1.25mm 9-pin header?

A 1.25mm header is a compact single-row connector with 1.25 mm center-to-center spacing; a 9-pin variant contains nine positions. Mechanical families include straight and right-angle, shrouded or unshrouded housings, and through-hole or SMT terminations. In the density hierarchy, it sits between micro wire-to-board pitches and legacy 2.54 mm systems, chosen when board real estate is constrained but logic-level currents are required.

Typical applications in product designs

Common uses include sensor harnesses, internal module interconnects, small display cables, and low-current signal buses. Designers often map I2C, SPI, UART, power, and several GPIOs to a single 9-pin connector for compact modules. The 9-pin PCB header is selected for space savings and sufficient current for logic and small peripherals, enabling compact breakouts and keyed debug ports.

1.25mm 9-Pin PCB Header Diagram

Mechanical & Electrical Specifications

Mechanical Dimensions (Nominal)

Pitch (Center-to-Center) 1.25 mm
Overall Length (9-Pin) ≈11.25 mm

*Tolerances typically ±0.05mm for pitch and ±0.1mm for overall length.

Electrical Ratings

Parameter Typical Rating
Current Rating ~1.0 A per pin
Contact Resistance 30–50 mΩ
Voltage (Withstand) 100V - 500V AC/DC
Plating Material Tin or Gold Flash

Pinout & Signal Assignment

Example Pinout Template (Mixed Signal & Debug)
Pin # Generic Signal (A) Debug/SWD (B) Description
1VCCVCC (3.3V)Main Power Supply
2GNDGNDSystem Ground
3UART_TXRESETTransmit / Reset Line
4UART_RXSWDIO / TMSReceive / Data I/O
5I2C_SCLSWCLK / TCKClock Signal
6I2C_SDASWO / TDOData Line / Output
7GPIO 1TDIGeneral Purpose / JTAG In
8GPIO 2UART_TXSecondary Comm
9GPIO 3UART_RXSecondary Comm

PCB Footprint Best Practices

  • ✔ Use rectangular through-hole annuli or oblong SMD pads sized to match plated pin diameter.
  • ✔ Specify paste coverage at 60–80% for SMT variants to prevent tombstoning.
  • ✔ Reserve keepout space for the mating housing to ensure clearance.
  • ✔ Always mark Pin 1 on the silkscreen with a dot or triangle.

Troubleshooting Checklist

Summary & Key Takeaways

Confirm pitch and variant early, document the exact pinout and footprint, and specify plating and current limits to avoid surprises in procurement and assembly.

Design: Verify 1.25mm pitch against vendor drawings before fabrication to avoid costly rework.
Electrical: Specify plating (Tin/Gold) in the BOM based on expected mating cycles.
Manufacturing: Include stencil specs and orientation fixtures in your assembly notes.

Frequently Asked Questions

What is the recommended current rating for a 1.25mm header pinout? +
Most small 1.25 mm pitch header families are rated around 1 A per pin for continuous service; final values depend on pin material, plating and thermal environment, so confirm the vendor datasheet for application-specific derating.
Should I use vias in pad for an SMD 1.25mm header footprint? +
Vias-in-pad are discouraged unless properly capped and plated because they can wick solder and create assembly defects. Prefer mechanical anchor vias outside pads or capped vias if thermal or grounding through-connection is required.
How do I document the 9-pin PCB header pinout for manufacturing? +
Include a clear pin table in the schematic and BOM with pin numbers, signal names, voltages and max currents; add the same table to the fabrication notes and the PCB silkscreen reference to eliminate ambiguity during assembly and service.

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