PCB Legend Print (Silkscreen): Design Guidelines, Rules, and Best Practices | PCB Power

Introduction

Legend print, also referred to as silkscreen, is used to apply text, symbols, or markings on top of the solder mask layer of a PCB.

It plays a critical role in identifying components, indicating polarity, marking reference designators, and adding useful information such as serial numbers or logos. In some cases, it is also used for visual representation or branding on the board.

Preparing Legend Print Data

Legend data should be provided as a separate layer for each side of the PCB where printing is required, typically labeled as Top Legend and Bottom Legend.

If native CAD files such as Eagle or KiCAD are shared, these layers are usually already included. Standard Gerber files also define silkscreen layers clearly.

Important:

Ensure that the PCB outline is included in the legend data. A thin line (around 0.5 mm width) centered on the board outline is recommended. This helps in alignment during processing and is removed before manufacturing.

Design Guidelines for Legend Print

Legend is typically printed on top of the solder mask layer. However, in traditional single-sided PCBs with through-hole components, it may be printed directly on the substrate.

To maintain clarity and avoid manufacturing issues, legend should not be placed on:

• Exposed copper surfaces
• Component pads
• Holes or cutouts

Proper placement ensures readability and prevents interference during assembly.

Text and Line Specifications

To achieve clear and readable markings, the following guidelines should be followed:

• Minimum line width: 0.10 mm (4 mil)
• Minimum text height: 1.00 mm

Designing within these limits helps maintain visibility after fabrication.

Clearance Requirements

For PCB Fabrication

Maintain minimum spacing between legend and other features:

• PCB edge: 0.25 mm (routing), 0.45 mm (scoring)
• Exposed copper: 0.10 mm
• Holes and cutouts: 0.10 mm

For PCB Assembly

To avoid interference during component placement:

• SMD component body: minimum 0.20 mm clearance
• Fine-pitch components (= 0.40 mm pitch): keep legend away from pad areas
• Small pads (< 0.32 mm): maintain sufficient distance to avoid overlap

These clearances help ensure smooth assembly and reduce the risk of defects.

Legend Clipping in Manufacturing

What is Legend Clipping?

Legend clipping is a pre-production adjustment where parts of the legend are trimmed or removed based on manufacturing constraints.

This process ensures that legend markings do not violate minimum spacing rules or interfere with critical PCB features.

How Clipping Works

During production preparation:

• The system checks legend against copper, holes, and board outline
• Any legend violating clearance rules is automatically adjusted
• Very thin or unreadable lines may be removed

In some cases, entire legend elements may be removed if they cannot meet manufacturing requirements.

Design Responsibility

While clipping helps maintain manufacturability, it is always recommended to follow proper legend placement guidelines during design itself.

Different manufacturers may follow slightly different rules based on their processes, so aligning your design with your manufacturing partner’s capabilities ensures better results.

Pre-Production Review

If you want to verify how your legend will appear after processing, you can request a pre-production review.

This allows you to compare your original legend data with the final production-ready version before manufacturing begins, helping avoid surprises later.

Conclusion

Legend print may seem like a small detail, but it plays a significant role in PCB usability, assembly accuracy, and long-term maintenance.

Well-designed legend ensures clear communication on the board, reduces errors during assembly, and supports better product reliability.

Legend design is reviewed as part of the DFM process at PCB Power, ensuring it aligns with real manufacturing and assembly conditions before production begins.

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