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Computer Components

Why Are Circuit Boards Green or Blue?

Circuit boards are usually green or blue because of the solder mask applied during manufacturing.

Solder Mask

This is a thin layer of polymer applied to the copper traces of the circuit board.

Its primary purpose is to prevent oxidation and to insulate the copper traces from accidental contact with other metal parts.

Color Choices

Green: The most common color, it’s traditionally used because it was the cheapest and most easily available.

Blue: Became popular as an alternative to green used in higher end or specialized applications for circuit boards. A majority of laptops these days have blue circuit boards. You’ve probably seen videos of people opening up laptops and 99% of the time, the circuit boards inside are blue with the exception of Macbooks maybe.

Reasons for the Green or Blue Prevalence

Historical: Early solder masks were green because of their epoxy resin composition.

Visibility: Green has a good contrast for visual inspection.

Cost: Green pigments were historically less expensive.

Other Colors

While green and blue are the most common, circuit boards can be made in any color like red, yellow, black or white. If you ever opened an iPhone or Macbook or you’ve seen videos on YouTube of people repairing Apple products, they never have green or blue circuit boards but rather black and white. This is to maintain a homogeneity across the device and appear more premium. The same can’t be said about Samsung phones or laptops from other companies.

Color choice is usually functional for example white for LED applications but sometimes it’s also for the aesthetic.

Functional Aspects

Some colors have slightly different thermal properties.

Certain colors are chosen for specific industries or applications.

Manufacturing Process

The color comes from pigments added to the solder mask material before application.

The mask is usually applied as a liquid and then cured with UV light or heat.

Color Coding

Some manufacturers use different colors to indicate the number of layers in a circuit board.

For example, green can be used for 2 layer boards, while blue indicates 4 or more layers.

Specialty Applications

White circuit boards are almost always used in LED applications for better light reflection.

Black circuit boards can be used in consumer electronics for aesthetic reasons or in military applications for heat dissipation.

Red circuit boards are sometimes used in prototyping to easily distinguish them from production boards.

Impact on Assembly

Lighter colors like white can make it easier to see solder joints during inspection.

Darker colors on the other hand can make it harder to see traces but reduce eye strain during long assembly processes.

Environmental Problems

Some newer solder mask formulations are more environmentally friendly, which is one of the main reasons why blue and green are being chosen more often.

RoHS (Restriction of Hazardous Substances) compliance has led to changes in PCB manufacturing, including solder mask compositions.

UV Resistance

Different colors will have varying levels of UV resistance, which is important for outdoor applications.

Thermal Properties

Darker colors absorb more heat, which can be either beneficial or detrimental depending on what you’re using the circuit board for.

Cost Factors

While green is still usually the cheapest, the price difference between colors has gone down a lot in recent years. Since blue also looks a little more premium and better that’s why it has been a more popular choice for circuit boards recently.

Custom colors can still be more expensive on average though.

Industry Trends

There’s a growing trend towards using circuit board color as a branding element, especially in consumer electronics.

Some high end products use unique or custom colors to differentiate themselves. Apple is definitely the best example I have at hand right now.

Photography and Documentation

Green circuit boards can be challenging to photograph because of the glare.

Some colors are preferred for technical documentation or marketing materials.

Regulatory Compliance

In some highly regulated industries (like aerospace or medical), the color of circuit boards are mandatory for consistency and traceability.

Optical Recognition

In automated assembly, certain colors like green and blue work better with optical recognition systems used for quality control.

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