Why are some PCBs red?

Introduction to PCBs and their color variations

Printed Circuit Boards (PCBs) are the backbone of modern electronics. These flat boards are used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate.

While the most common color for PCBs is green, they can come in a variety of colors including blue, yellow, black and red. The color of a PCB is determined by the solder mask, which is a thin layer of polymer applied over the copper traces to protect them from oxidation and short circuits.

In this article, we will explore the reasons why some PCBs are red and the benefits and drawbacks of using red PCBs in electronic devices. We will also discuss how red PCBs are manufactured and answer some frequently asked questions about red PCBs.

The history of red PCBs

Red PCBs have been around since the early days of PCB manufacturing. In the 1960s and 1970s, red solder mask was commonly used because it was one of the few colors available at the time. Red solder mask was made from a pigment called “resine red” which was mixed with the solder mask polymer.

As PCB manufacturing technology advanced, more solder mask colors became available and green became the most popular choice due to its better visibility and contrast with the white silkscreen legend. However, red PCBs are still used today for various reasons which we will discuss later in this article.

How are red PCBs manufactured?

The manufacturing process for red PCBs is similar to that of other colored PCBs. Here is a simplified overview of the steps involved:

  1. Designing the PCB layout: The first step is to design the circuit diagram and PCB layout using CAD software. The layout specifies the location and routing of the copper traces, components, and drill holes.

  2. Printing the photoresist film: The PCB layout is printed onto a transparent photoresist film which will be used to transfer the circuit pattern onto the copper-clad board.

  3. Laminating the photoresist film: The photoresist film is laminated onto the copper-clad board using heat and pressure.

  4. Exposing and developing the photoresist: The laminated board is exposed to UV light through the photoresist film, hardening the areas not covered by the opaque circuit pattern. The unexposed areas are then removed using a chemical developer solution, leaving only the hardened photoresist covering the circuit pattern.

  5. Etching the copper: The exposed copper areas are etched away using a chemical etchant solution, leaving only the copper traces protected by the hardened photoresist.

  6. Applying the solder mask: The red solder mask ink is applied over the entire board and then exposed and developed like the photoresist, leaving openings for the copper pads and any exposed traces.

  7. Applying the silkscreen legend: The white silkscreen legend ink is applied on top of the solder mask to label components and provide other information.

  8. Surface finish: A surface finish such as HASL (Hot Air Solder Leveling) or ENIG (Electroless Nickel Immersion Gold) is applied to the exposed copper pads to protect them from oxidation and facilitate soldering.

  9. Cutting and drilling: Finally, the board is cut to its final shape and any required holes are drilled.

Advantages of using red PCBs

There are several reasons why a designer might choose to use a red PCB instead of the more common green color:

1. Aesthetics and branding

One of the main reasons for using a red PCB is for aesthetic and branding purposes. Red is a bold and eye-catching color that can make a product stand out from the competition. Many companies use red PCBs in their products as part of their brand identity.

For example, the Italian luxury sports car manufacturer Ferrari is known for using red PCBs in their vehicles’ electronic systems. The red color is synonymous with the Ferrari brand and using red PCBs helps to reinforce this association in the minds of customers.

2. Improved contrast and visibility

Another advantage of red PCBs is that they provide better contrast and visibility than green PCBs in certain lighting conditions. Under low light or when viewed through a colored filter, the red solder mask can make the white silkscreen legend more readable.

This is especially important in applications where the PCB needs to be easily visible and readable, such as in industrial control panels or medical devices. The improved contrast and visibility can help to reduce errors and improve the user experience.

3. Reduced eye strain

Staring at a bright green PCB for extended periods of time can cause eye strain and fatigue, especially in low light conditions. The red color is less harsh on the eyes and can help to reduce eye strain and improve comfort during long work sessions.

This is particularly important for electronics technicians, engineers, and hobbyists who spend a lot of time working with PCBs. Using a red PCB can help to reduce eye strain and improve productivity.

4. Improved heat dissipation

Another potential advantage of red PCBs is that they may have better heat dissipation properties than green PCBs. The red solder mask may have a higher thermal conductivity than the green solder mask, allowing heat to be dissipated more efficiently from the copper traces and components.

This can be especially important in high-power applications where heat generation is a significant concern. By using a red PCB, designers may be able to reduce the need for additional cooling measures such as heatsinks or fans.

Disadvantages of using red PCBs

While there are several advantages to using red PCBs, there are also some potential drawbacks to consider:

1. Limited availability and higher cost

One of the main disadvantages of red PCBs is that they are less common than green PCBs and may be more difficult to source. Not all PCB manufacturers offer red solder mask as a standard option, and those that do may charge a premium for it.

This limited availability and higher cost can be a barrier for some designers, especially those working on low-volume or low-cost projects. In some cases, the benefits of using a red PCB may not justify the additional expense.

2. Potential for color inconsistency

Another potential issue with red PCBs is the potential for color inconsistency between different batches or suppliers. The exact shade of red can vary depending on the specific solder mask ink used and the manufacturing process.

This can be a problem if color consistency is important for branding or aesthetic reasons. It may be necessary to work closely with the PCB manufacturer to ensure that the desired shade of red is achieved consistently.

3. Reduced legibility of silkscreen legend

While red PCBs can provide better contrast and visibility for the white silkscreen legend in certain lighting conditions, they may actually reduce the legibility of the legend in other conditions.

Under bright light or when viewed at certain angles, the white silkscreen may appear washed out or difficult to read against the red background. This can be a particular problem for dense or complex PCB layouts with a lot of small text.

Designers may need to take extra care to ensure that the silkscreen legend is legible and easy to read under all expected viewing conditions.

Frequently Asked Questions (FAQ)

1. Are red PCBs more expensive than green PCBs?

Yes, red PCBs are generally more expensive than green PCBs due to the limited availability of red solder mask and the potential for higher manufacturing costs. However, the exact price difference can vary depending on the specific manufacturer and the volume of the order.

2. Can red PCBs be used for all applications?

Red PCBs can be used for most applications, but there may be some cases where they are not suitable. For example, in applications where color consistency is critical for branding or aesthetic reasons, the potential for color variations between batches may be a concern.

3. Do red PCBs have any effect on signal integrity?

The color of the solder mask should not have any significant effect on signal integrity. The dielectric properties of the solder mask material are more important than the color in terms of their impact on signal propagation and impedance.

4. Are there any special handling or storage requirements for red PCBs?

Red PCBs do not have any special handling or storage requirements compared to other colors. As with all PCBs, they should be stored in a cool, dry place away from direct sunlight and sources of heat or humidity to prevent damage or degradation.

5. Can red PCBs be recycled?

Yes, red PCBs can be recycled just like any other color of PCB. The recycling process involves separating the metal components (such as copper and gold) from the non-metallic substrate material. The color of the solder mask does not affect the recyclability of the PCB.

Conclusion

In conclusion, red PCBs are a viable alternative to the more common green PCBs and offer several potential benefits such as improved aesthetics, better contrast and visibility, reduced eye strain, and improved heat dissipation.

However, there are also some potential drawbacks to consider, such as limited availability, higher cost, color inconsistency, and reduced legibility of the silkscreen legend in certain conditions.

Ultimately, the decision to use a red PCB will depend on the specific requirements and constraints of the project, as well as the designer’s personal preferences and priorities.

By understanding the advantages and disadvantages of red PCBs, designers can make informed decisions about whether they are the right choice for their particular application.

Advantages of Red PCBs Disadvantages of Red PCBs
Aesthetic and branding appeal Limited availability and higher cost
Improved contrast and visibility in certain conditions Potential for color inconsistency between batches
Reduced eye strain and fatigue Reduced legibility of silkscreen legend in certain conditions
Potential for improved heat dissipation May not be suitable for all applications

Regardless of the color chosen, PCBs play a critical role in the functioning of modern electronic devices and will continue to be an essential component in the design and manufacturing process for the foreseeable future.

As PCB technology continues to evolve and new materials and manufacturing techniques are developed, we can expect to see even more options and innovations in PCB design and fabrication, including new colors and finishes that offer unique benefits and possibilities.