Why Are Tooling Holes Important in PCB Design and Assembly?

When designing a PCB, engineers often focus on electrical performance, component placement, routing, and mechanical dimensions. However, some holes on a PCB are not related to electrical functions at all.

Tooling holes are one example. They are primarily designed to assist with PCB manufacturing, positioning, and assembly.

This Gold Phoenix PCB Knowledge Center article explains the purpose of tooling holes, where they are commonly used, and why they are important during PCB manufacturing and assembly.

What Are Tooling Holes?

A tooling hole is a dedicated hole used as a mechanical reference point during PCB fabrication and assembly.

Unlike component holes, tooling holes are generally not intended for electrical connections. Their main purpose is to help equipment accurately position and hold the PCB during different manufacturing processes.

Where Are Tooling Holes Used?

Tooling holes may be used during several stages of PCB production and assembly, including:

• SMT Assembly – Helps accurately position the PCB on assembly equipment.

• Stencil Printing – Provides reference points for aligning the PCB with the solder paste stencil.

• AOI Inspection – May assist with consistent PCB positioning during automated inspection.

• Wave Soldering – Can assist with securing and positioning the PCB during the soldering process.

• Panelization – Helps maintain consistent positioning of individual boards within a production panel.

Why Are Tooling Holes Important?

During automated manufacturing, even a small positioning error can affect solder paste printing, component placement, inspection, or soldering quality.

Tooling holes provide fixed mechanical reference points, allowing equipment to repeatedly position the PCB in a consistent location.

This can be especially important for boards with:

• Fine-pitch components

• Small passive components

• BGA or other high-density packages

• Tight component-to-pad tolerances

• High-precision SMT requirements

Where Should Tooling Holes Be Placed?

Tooling holes are commonly placed on the PCB’s process edge (rail) or in other designated mechanical reference areas.

For panelized boards, their position should also be considered together with:

• Panel dimensions

• Board orientation

• Component placement

• Stencil design

• SMT machine requirements

• Depanelization method

The exact location and size should follow the requirements of the PCB assembly process and manufacturing equipment.

Tooling Holes vs. Component Holes

The key difference is their purpose.

Component holes are part of the electrical or mechanical function of the finished product, such as mounting component leads or connectors.

Tooling holes, on the other hand, primarily serve the manufacturing process.

In simple terms:

Component holes serve the product; tooling holes serve the manufacturing process.

What If a PCB Does Not Have Tooling Holes?

Not every PCB necessarily requires dedicated tooling holes. Depending on the board design and assembly process, manufacturers may use other positioning features or fiducials for alignment.

However, for automated SMT assembly and high-precision manufacturing, suitable mechanical reference features can help make the production process more stable and repeatable.

Therefore, tooling-hole requirements are best considered during the PCB design stage, rather than added only after the board has entered production.