Known as the "mother of electronic components", printed circuit boards (PCBs) play an indispensable role in electronic applications. Based on distinct design principles, PCBs can be categorized into several types, including single-layer boards, multi-layer boards, flexible boards, rigid boards, and rigid-flex combined boards.

Currently, the most common PCB colors available on the market are green, black, blue, yellow, purple, red, and brown. In recent times, white and pink PCBs have also made their appearance. Have you ever wondered why PCBs come in such a variety of colors? And why is green the dominant color, while other hues are relatively rare? Let’s delve into some essential knowledge about PCBs to answer these questions.

Why Do PCBs Come in Different Colors?

During PCB manufacturing, regardless of whether the additive or subtractive method is used, the final surface of the copper layer remains smooth and unprotected. Although copper is less reactive than metals like aluminum, iron, and magnesium, the copper layer on PCBs is extremely thin. When exposed to oxygen and moisture, copper oxidizes, and oxidized copper becomes a poor electrical conductor—this can severely impair the overall electrical performance of the PCB.

To prevent copper oxidation, distinguish between soldered and non-soldered areas on the PCB, and protect the board’s surface, design engineers apply a special coating to form a protective layer of a specific thickness, which blocks copper from coming into contact with air. This coating is called a solder mask, and it is made from solder mask ink. Additionally, to facilitate manufacturing and maintenance, PCBs often require small text to be printed on their surface. As a result, engineers add various colors to the solder mask ink, leading to the creation of colorful circuit boards.

Why Is Green Ink Widely Used?

Green solder mask ink is currently the most widely used and cost-effective option on the market. While solder mask inks come in a range of colors—such as red, blue, purple, black, and yellow—green remains the most prevalent. The main reasons for this are as follows:

First, it aids instrument identification. The color of the solder mask layer is determined by the color of the solder mask ink. The PCB manufacturing process includes SMT soldering, which involves tinning and final AOI inspection. These processes rely on optical positioning for calibration, and a green background enhances instrument recognition accuracy. Moreover, green PCBs offer better visual clarity in yellow light rooms, which are commonly used in PCB manufacturing and SMT processing. This makes it easier for workers to inspect the production quality of electronic products.

Second, it is easier for workers to inspect the circuit board. Despite the widespread use of flying probe testing technology, many production lines still rely on manual visual inspection for quality control due to process limitations. Staring at a circuit board under bright lights for extended periods can be tiring. Green, as a background color, helps reduce eye strain caused by strong light, which is why most manufacturers opt for green PCBs.

Third, it is environmentally friendly and cost-effective. When discarded, PCBs need to be recycled at high temperatures. Green solder mask ink does not release toxic gases during this process, making it more environmentally friendly. Additionally, green solder mask ink has the highest adoption rate and the most mature production process, which translates to lower costs for manufacturing PCBs with green solder masks.

Are Black PCBs More Expensive and High-End?

Many high-end electronic products use black PCBs, leading people to mistakenly believe that black PCBs are more expensive and of higher quality. In reality, this perception is incorrect. The only difference between black PCBs and those of other colors lies in the type of solder mask ink used. If two PCBs have the same design and manufacturing process, their color has no impact on performance or heat dissipation.

In fact, black PCBs have certain drawbacks: their surface circuits are almost entirely concealed, making post-maintenance extremely difficult. Additionally, black PCBs are the most challenging to drill, resulting in a lower yield rate compared to PCBs of other colors. These factors contribute to the relatively higher cost of black PCBs.

The misconception that "color determines product grade" arises from manufacturers’ tendency to use black PCBs for high-end products and colors like red, blue, green, and yellow for low-end models. The key point is: it is the product that gives meaning to the color, not the color that defines the product. Whether a PCB is black or green, it is a high-quality board if it boasts excellent performance and efficient heat dissipation.

The choice of PCB color reflects the emergence, development, and adoption of new technologies in the evolution of modern science and technology. While the invention and development of PCBs have driven the progress of numerous electronic industries, PCBs themselves are constantly evolving and innovating. In the near future, it is possible that PCBs of other colors will replace the current dominance of green—let us wait and see what the future holds.