Why Are Circuit Boards Green and What’s the Significance?

Perhaps some people like the color green, but it is believed that they are definitely not Chinese, especially when ‘green’ is associated with a ‘hat’ (meaning being cuckolded). Green is a color that is frequently used in the electronics industry. For example, it constitutes the majority of the primary color scheme for printed circuit boards. So, why is the usage of green PCB so high? What impact does green have on a circuit? What special significance does green hold in a PCB?

green circuit board

Table of Contents

What Is Green on a PCB

A printed circuit board is like a sandwich, consisting of different layers stacked together, including inner layers, copper foil layers, insulation layers, solder mask layers, and silkscreen layers, among others. The topmost layer on the PCB is the solder mask and silkscreen layer, which is the part directly visible to the user. The white text is the silkscreen, while the green part is the solder mask layer. So when we talk about a green circuit board, we are actually referring to a PCB where the solder mask layer is green.

what are green circuit boards made of

As a platform for electrical connections, the components on a PCB rely on the copper trace on the PCB surface for connectivity. However, this trace is very fragile, and even slight scratches can damage signal integrity. This is where the solder mask layer comes into play. Manufacturers apply solder mask ink to the surface of the PCB during the manufacturing process and then cure it using a UV machine to achieve the purpose of protection. In other words, the green part on a PCB serves the purpose of protection and is unrelated to the circuit’s performance. If you don’t want a green PCB, you can simply change the color of the solder mask ink.

Nowadays, PCB colors can be diverse, and users can choose green, red, yellow, or any other color based on their preference. But why do we usually see the circuit board is green?

Historical Inheritance

Firstly, this has a slight connection to historical heritage. PCB originated in the early 20th century when there were limited options due to technological limitations and material scarcity. Green was chosen as the primary color for PCB among the limited options available at that time. With technological advancements, this technology was recognized by the U.S. military and became exclusive to the military sector. The green color of PCB remained consistent with the color of the U.S. Army uniforms of the time and was not changed. When later used in the commercial sector, the focus shifted more toward performance rather than aesthetics, and this tradition has continued. Nowadays, printing technology has become quite mature, and it has given rise to more personalized demands. However, green PCB is still considered the default option.

Further reading: The history of PCB development

Cost Factor

A key factor here is the cost. In commercial projects, manufacturers often purchase essential materials in bulk in advance, such as solder mask ink, solder paste, and general components. Due to bulk purchasing, they can often achieve economies of scale, resulting in lower procurement costs. As green PCB is the default option, manufacturers stock a significantly higher quantity of green solder mask ink than other colors, making green PCB slightly less expensive than PCB of other colors. Additionally, since green PCB is more commonly used, the stockpiled quantities are less likely to go to waste. However, extremely rare options like purple or pink, typically do not appear on the list of materials in stock. Instead, they are ordered when receiving a specific order, which leads to increased unit prices.

Moreover, during procurement, to avoid the risk of material loss causing production delays, a surplus is often set. This can result in unused ink after completing orders, which may not be used again, ultimately leading to waste. You might think these losses are borne by the manufacturers and have nothing to do with users. Well, it appears you might be a bit naive. Nearly all manufacturers are “capitalists” and they always prioritize “money.” They calculate potential losses that may occur during the production process and factor them into your quotation. This includes issues like the yield rate problems associated with high standards, faults related to special materials, and material usage losses. Consequently, the price of green PCB ends up being higher than others. Unlike other products that focus on appearance, PCB prioritize performance, and most users are not willing to pay extra just for aesthetics. This situation, combined with the high frequency of green PCB usage, creates a cycle, and that’s why most PCB we see are green.

Sharp Contrast

The difference between green and white is more obvious

Furthermore, let’s connect the PCB color with the silkscreen layer mentioned earlier. The silkscreen is a set of characters and numbers written on the surface of the PCB, serving as a guide for circuit board maintenance to locate and identify components. Ease of readability is the only criterion for silkscreen design. In commercial projects, the silkscreen is usually black or white. Black silkscreen is used on white PCB to make it visible, while white silkscreen is used on PCB of any other color. Among different PCB colors, green displays the silkscreen font better. You can conduct an experiment: write with a white pen on papers of different colors and see which one is the most legible. Clearly, black, blue, and green work best, while yellow performs less effectively.

Processing Difficulty

Another key factor is to avoid the color having an impact on the production and processing of the project. As mentioned earlier, black is a favorite color among designers, giving the PCB a sense of sophistication. However, for manufacturers, black can be a bit of a “nightmare.” This is not because black solder mask ink is more expensive or difficult to obtain, but rather because production processes can encounter certain issues. Different users have varying acceptance criteria for PCB; for example, IPC-610-A-G may not specify scratch requirements, but some standards may have strict demands in this regard. Black PCB is challenging to inspect for surface imperfections, requiring inspectors to tilt them under specific lighting conditions, making inspection more difficult. In contrast, green PCB does not pose such concerns. Manufacturers can easily process these boards. Although modern electronic systems rely heavily on automated intelligent processing, they still require manual labor, such as manual inspection and assembly. When dealing with large quantities of projects, manual labor can lead to worker fatigue. However, green helps alleviate this fatigue, which may be another reason why people prefer to use green PCB.

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