Designing and Placing Silkscreen on Your PCB with Altium Designer

 

Introduction

Designing and placing silkscreen on a Printed Circuit Board (PCB) is a crucial step in the PCB design process. Silkscreen, also known as legend or screenprint, provides essential information for assembly, testing, and maintenance of the board. Altium Designer, a powerful PCB design software, offers robust tools for creating and managing silkscreen elements. This comprehensive guide will walk you through the process of designing and placing silkscreen on your PCB using Altium Designer, covering everything from basic concepts to advanced techniques.

Understanding Silkscreen

What is Silkscreen?

Silkscreen is a layer of text and symbols printed on the surface of a PCB. It typically appears in white or yellow ink on the top and bottom sides of the board. The primary purpose of silkscreen is to provide visual information about the board's components, connections, and functionality.

Importance of Silkscreen

Silkscreen plays several crucial roles in PCB design and usage:

1. Component identification
2. Pin and connection labeling
3. Polarity indicators
4. Warnings and instructions
5. Company logos and board identifiers

Types of Silkscreen Elements

Common silkscreen elements include:

Element Type
Description
Examples
Text
Alphanumeric characters for labeling
Component designators, pin numbers
Symbols
Graphical representations
Polarity indicators, warning signs
Lines and shapes
Visual aids for component placement
Component outlines, keep-out areas
Logos
Company or product branding
Manufacturer's logo, certification marks

Altium Designer Overview

Introduction to Altium Designer

Altium Designer is a comprehensive PCB design software that offers a wide range of tools for creating and editing PCB layouts, including silkscreen design. Its user-friendly interface and powerful features make it a popular choice among PCB designers.

Key Features for Silkscreen Design

Altium Designer provides several features specifically for silkscreen design:

1. Text and string placement tools
2. Symbol libraries
3. Custom shape creation
4. Layer-specific editing
5. Design rule checking for silkscreen

Silkscreen Layers in Altium Designer

Altium Designer uses specific layers for silkscreen:

Layer Name
Description
Top Overlay
Silkscreen on the top side of the PCB
Bottom Overlay
Silkscreen on the bottom side of the PCB
Top Paste
Stencil layer for solder paste on the top side
Bottom Paste
Stencil layer for solder paste on the bottom side

Preparing Your PCB Design

Setting Up Your Project

Before you start designing your silkscreen, ensure your PCB project is properly set up:

1. Create a new PCB project in Altium Designer
2. Set up your board outline and stackup
3. Place components on your PCB
4. Route connections between components

Configuring Silkscreen Layers

To prepare for silkscreen design:

1. Enable the Top Overlay and Bottom Overlay layers
2. Set appropriate colors for easy visibility
3. Configure layer stack manager to include silkscreen layers

Defining Design Rules

Establish design rules for silkscreen to ensure manufacturability:

1. Set minimum text height and width
2. Define clearances between silkscreen and other board elements
3. Specify allowed fonts and character sets

Creating Silkscreen Elements

Adding Text

To add text to your silkscreen:

1. Select the appropriate overlay layer
2. Use the 'Place String' tool
3. Choose font, size, and orientation
4. Position the text on the board

Placing Symbols

For symbols and graphical elements:

1. Use the 'Place Symbol' tool
2. Select from Altium's symbol libraries or create custom symbols
3. Adjust size and orientation as needed
4. Position the symbol on the board

Creating Custom Shapes

To create custom silkscreen shapes:

1. Use the drawing tools (line, arc, polygon)
2. Ensure the shape is on the correct overlay layer
3. Adjust line width and fill properties

Importing Graphics

For logos or complex graphics:

1. Prepare the graphic in a vector format (e.g., DXF)
2. Use the 'Import' function to bring the graphic into Altium Designer
3. Assign the imported graphic to the appropriate overlay layer
4. Scale and position as needed

Placing Silkscreen on Your PCB

Component Designators

For component designators:

1. Use automatic designator placement tools
2. Adjust positions manually for clarity
3. Ensure consistency in size and orientation

Pin Labels

To label pins:

1. Use the 'Place String' tool near each pin
2. Align labels consistently with pin orientation
3. Avoid overlapping with other board elements

Polarity Indicators

For components with polarity:

1. Place standard polarity symbols (e.g., plus sign, band)
2. Ensure symbols are clearly visible and not obscured by components

Reference Designators

To add reference designators:

1. Place text near each component
2. Use a consistent naming scheme
3. Ensure designators are easily readable

Board Identifiers

For board identification:

1. Add board name, revision number, and date
2. Place company logo if desired
3. Include any necessary certification marks

Best Practices for Silkscreen Design

Readability

To ensure your silkscreen is readable:

1. Use appropriate font sizes (minimum 50 mil height recommended)
2. Choose clear, sans-serif fonts
3. Maintain consistent orientation of text
4. Ensure adequate contrast with board color

Placement

For optimal silkscreen placement:

1. Avoid placing silkscreen on pads or vias
2. Leave clearance around component bodies
3. Align text and symbols with component edges when possible
4. Consider viewing angle and component heights

Consistency

Maintain consistency across your design:

1. Use standardized symbol sizes and styles
2. Apply uniform text heights for similar information types
3. Align elements to a grid where possible

Information Hierarchy

Organize information effectively:

1. Use larger text for more important information
2. Group related information together
3. Use different text styles to differentiate information types

Manufacturing Considerations

Keep manufacturing limitations in mind:

1. Adhere to minimum feature size requirements
2. Avoid intricate details that may not reproduce well
3. Consider the impact of different board finishes on silkscreen visibility

Advanced Silkscreen Techniques

Multi-layer Silkscreen

For complex designs, consider using multiple silkscreen layers:

1. Use different colors for different types of information
2. Leverage both top and bottom overlays effectively
3. Coordinate with your manufacturer to ensure feasibility

Dynamic Silkscreen Generation

Automate silkscreen creation:

1. Use Altium Designer's scripting capabilities
2. Create custom scripts for repetitive silkscreen tasks
3. Integrate with BOM data for automatic designator generation

Incorporating Assembly Instructions

Include assembly guidance in your silkscreen:

1. Add component orientation markers
2. Include brief assembly notes where space allows
3. Consider using QR codes linking to detailed instructions

Silkscreen for Flexible PCBs

When designing for flex PCBs:

1. Account for bending areas in silkscreen placement
2. Use more durable silkscreen materials if available
3. Consider the impact of flexing on silkscreen readability

Troubleshooting Common Silkscreen Issues

Overlapping Elements

To resolve overlapping silkscreen elements:

1. Use Altium's Design Rule Check (DRC) to identify overlaps
2. Adjust element positions or sizes manually
3. Consider using abbreviations or smaller fonts where space is limited

Missing or Truncated Text

If text is missing or truncated:

1. Check layer visibility settings
2. Verify text fits within board boundaries
3. Adjust text size or position as needed

Silkscreen on Pads or Vias

To remove silkscreen from pads or vias:

1. Use the "Remove From Pad" option in Altium Designer
2. Adjust clearance rules for silkscreen
3. Manually edit problematic areas

Inconsistent Text Sizes

To maintain consistent text sizes:

1. Use Altium's text style presets
2. Leverage global editing tools to update multiple elements at once
3. Perform a visual check and measurement of text heights

Poor Contrast

If silkscreen contrast is inadequate:

1. Adjust board and silkscreen colors in Altium's display settings
2. Consider changing the physical board color if possible
3. Use bold or wider text styles for better visibility

Exporting and Manufacturing Considerations

Generating Gerber Files

To prepare your design for manufacturing:

1. Use Altium's Gerber export function
2. Include both Top and Bottom Overlay layers
3. Verify Gerber file settings match manufacturer requirements

Reviewing Silkscreen in Gerber Viewers

Before sending to manufacture:

1. Use a Gerber viewer to check silkscreen appearance
2. Verify all elements are present and correctly positioned
3. Check for any artifacts or unintended elements

Communicating with Manufacturers

When sending your design for production:

1. Provide clear instructions regarding silkscreen color and finish
2. Specify any critical silkscreen elements that must be preserved
3. Request a silkscreen proof if available

Considering Different Board Finishes

Be aware of how board finishes affect silkscreen:

Board Finish
Silkscreen Considerations
HASL
May cause uneven silkscreen surface
ENIG
Provides good contrast with white silkscreen
OSP
May require adjusted silkscreen color for visibility
Immersion Silver
Can offer good contrast, but may tarnish over time
Immersion Tin
May require darker silkscreen colors for visibility

Conclusion

Designing and placing silkscreen on your PCB using Altium Designer is a crucial step in creating a functional and user-friendly board. By following the guidelines and best practices outlined in this article, you can ensure that your silkscreen provides clear, readable, and valuable information for assembly, testing, and maintenance of your PCB.

Remember to consider readability, consistency, and manufacturing limitations throughout the design process. Leverage Altium Designer's powerful tools to create professional-looking silkscreen layouts that enhance the usability and appearance of your PCBs.

As you gain experience, don't hesitate to explore advanced techniques and automate repetitive tasks to streamline your workflow. With practice and attention to detail, you'll be able to create silkscreen designs that not only meet functional requirements but also contribute to the overall quality and aesthetic appeal of your PCB projects.

Frequently Asked Questions

Q1: What is the minimum text size recommended for PCB silkscreen?

A1: The minimum recommended text size for PCB silkscreen is typically 50 mils (0.050 inches or 1.27 mm) in height. However, this can vary depending on the manufacturer's capabilities and the specific requirements of your project. It's always best to check with your PCB manufacturer for their specific minimum size recommendations.

Q2: Can I use different colors for silkscreen on the same PCB?

A2: While it is technically possible to use multiple colors for silkscreen on the same PCB, it's not common practice due to increased manufacturing complexity and cost. Most PCBs use a single color for silkscreen, typically white or yellow. If you require multiple colors, discuss this with your manufacturer to understand the feasibility and associated costs.

Q3: How do I ensure my silkscreen doesn't interfere with solder mask?

A3: To prevent silkscreen from interfering with solder mask:

1. Use Altium Designer's design rules to set appropriate clearances between silkscreen and pads/vias.
2. Utilize the "Remove From Pad" option when placing silkscreen elements.
3. Perform a Design Rule Check (DRC) to identify any violations.
4. Visually inspect your design in both 2D and 3D views to ensure proper clearance.

Q4: Is it necessary to include silkscreen on both sides of the PCB?

A4: Including silkscreen on both sides of the PCB is not always necessary, but it can be beneficial depending on your design. Top-side silkscreen is most common and usually sufficient for many designs. However, bottom-side silkscreen can be useful for:

1. Double-sided boards with components on both sides
2. Providing additional information for testing or maintenance
3. Including board identification or certifications when top-side space is limited

Consider the specific needs of your project when deciding whether to use single-sided or double-sided silkscreen.

Q5: How can I create custom symbols for my silkscreen in Altium Designer?

A5: To create custom symbols for silkscreen in Altium Designer:

1. Open the PCB Library Editor
2. Create a new PCB symbol
3. Use drawing tools (line, arc, polygon) to create your symbol on the appropriate overlay layer
4. Save the symbol to your library
5. Use the "Place Symbol" tool in your PCB document to add the custom symbol to your design