What is a Yellow PCB?

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Introduction

A printed circuit board (PCB) is a board made of fiberglass or other composite material that provides the foundation for mounting and wiring electronic components. PCBs allow electrical connections between components without the need for wiring everything point-to-point.

PCBs come in a variety of colors, with green, blue, and white being some of the most common. However, yellow PCBs have grown in popularity in recent years. This article will explore what a yellow PCB is, why someone may choose a yellow PCB, and the pros and cons of using yellow PCBs.

What is a Yellow PCB?

A yellow PCB is a printed circuit board that has a yellow solder mask rather than the traditional green solder mask. The solder mask is the protective coating applied over the copper traces on a PCB to prevent solder bridges from forming between closely spaced pads during assembly.

The solder mask color does not affect the function or performance of the PCB. The choice of solder mask color is purely aesthetic. However, some engineers and designers choose yellow solder masks because they offer better contrast and visibility compared to traditional green.

Why Choose Yellow?

Here are some of the reasons why someone may choose a yellow solder mask for their PCB:

  • Increased contrast – The yellow solder mask provides higher contrast against the metallic traces and pads, making it easier to visually inspect the board.
  • Improved inspection – Flaws and defects can be easier to spot on yellow PCBs compared to green. The color provides better optical definition.
  • Easier rework – Reworking or repairing a PCB is simpler with the higher contrast of a yellow solder mask. Component markings and labels are also easier to read.
  • Aesthetic choice – Some engineers and designers simply prefer the look of a yellow PCB over green. The color helps the PCB stand out.
  • Branding – For some companies, having a distinct PCB color can aid in brand recognition. Yellow solder masks can assist with marketing and product identity.

Yellow Solder Mask Materials

The yellow solder mask color is achieved by adding pigments to the standard solder mask materials:

  • Liquid photoimageable solder mask (LPC) – This is the most common solder mask applied by screen printing or spray coating. A photo process is used to cure and harden the mask.
  • Dry film solder mask – The solder mask comes as a solid laminate sheet. The sheet is vacuum laminated onto the PCB and then exposed/cured.
  • UV curable solder mask ink – These are solder mask inks cured with UV light, providing a more environmentally friendly process.

The specific pigments and dyes used to color the solder mask yellow can vary between material manufacturers. But all offer a visually equivalent yellow color.

Pros and Cons of Yellow PCBs

Below are some of the key pros and cons to consider when deciding whether to use a yellow solder mask on a printed circuit board design:

Pros

  • Improved inspectability and visual clarity
  • Easier manual and automated optical inspection (AOI)
  • Simplified PCB rework and repair
  • Enhanced contrast for easier assembly
  • Distinctive aesthetic appearance
  • Aid for branding and product recognition

Cons

  • Potential for higher solder mask costs
  • Color availability may be limited by PCB manufacturer
  • Atypical color may confuse those used to green PCBs
  • Contrast benefits diminished if using predominantly yellow components
  • Slight increase in lead time for custom color availability

Applications and Use Cases

Yellow PCBs lend themselves well to certain applications and use cases where the visual clarity is beneficial. Some examples include:

High Density Interconnect (HDI) PCBs

HDI PCBs have trace spacing and line widths under 100 microns. Yellow solder masks greatly improve the inspectability and enhance the contrast on these dense boards.

RF/Microwave PCBs

The small features and spacings of high frequency RF PCBs also benefit from the superior contrast of yellow masks. Enhanced visibility aids manual and automated inspection.

Test Points and Testability

Yellow solder masks make logical and functional test points stand out. This aids in-circuit testing and troubleshooting workflows.

Low Volume or Prototype PCBs

When producing short runs of prototype PCBs, the extra visual clarity helps validate assembly and functionality. Yellow masks also give prototypes a more finished look.

LED Lighting

For LED lighting applications, yellow masks provide good contrast against the typical black substrates used. The yellow-black patterning meshes well with LED lighting aesthetics.

PCB Design and Manufacturing Considerations

There are some important considerations when designing a PCB with a yellow solder mask and selecting a PCB manufacturer:

Solder Mask Color Availability

Not all manufacturers offer yellow solder masks on all of their PCB materials/stacks. Check color availability and lead times upfront.

Cost

Expect moderately higher cost for custom solder mask colors. Exact pricing difference depends on the manufacturer and order volume.

Design File Requirements

Ensure design files specify yellow solder mask or provide a separate solder mask layer in the CAD data.

Mask Tolerancing

Slight registration differences may be more visible. Discuss tolerancing needs with your PCB manufacturer.

Quality Expectations

Establish acceptable quality limits on color consistency and color matching upfront.

Pad Color

Request black pad color on surface mount pads for optimal contrast against yellow solder mask.

Silkscreen Color

Use white or black silkscreen colors for best visibility against a yellow mask. Avoid red or blue silkscreens.

Inspectability Testing

Perform testing to confirm enhanced inspectability meets expectations versus standard green solder masks.

Conclusion

Yellow PCBs offer a unique aesthetic appearance while providing improved visual contrast and inspection capabilities in certain applications. The heightened visibility simplifies validation and enhances quality control.

However, yellow solder masks also have cost and lead time implications, and introduce some tolerancing challenges. Carefully weigh the tradeoffs against the benefits for your particular PCB requirements. Collaborate with your PCB manufacturer early in the design process if pursuing a yellow PCB.

Frequently Asked Questions

What is the difference between a green and yellow PCB?

The only difference is the color of the solder mask. Green solder masks are standard, while yellow masks are a custom option used for enhanced visual clarity and aesthetics. The solder mask color does not impact function or electrical performance.

Does a yellow PCB cost more than a green PCB?

Typically, yes. Custom solder mask colors often incur moderately higher costs with PCB manufacturers. Exact pricing difference depends on factors like order volume and manufacturer capabilities.

Why was green historically the color used for PCBs?

Early PCBs used masking lacquers that were naturally green in color. As solder masks evolved from lacquers to liquid photoimageable or dry film, green persisted as the standard color.

Does a yellow solder mask affect reliability or durability?

No. Leading solder mask materials can be pigmented to achieve a yellow color while maintaining the same reliability and durability expected of a solder mask. The color itself does not impact performance.

Can any PCB manufacturer make yellow PCBs?

Not always. Some manufacturers may not offer custom solder mask colors or have limited color palette options. Check with potential fabricators on their yellow PCB capabilities and lead times.

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