Many people tend to assess the quality of a motherboard based on the color of the PCB substrate. However, the color of the motherboard is not directly linked to its performance. The surface color of the PCB is actually determined by the solder resist (also known as solder mask). Its primary purpose is to prevent electrical components from being incorrectly soldered during the manufacturing process. Additionally, it serves another vital function: protecting soldered components from oxidation and corrosion during use, thereby reducing the failure rate.
Typically, you’ll notice that the PCB boards of large companies like Huawei and ZTE are predominantly green. This is because the green solder mask process is the most mature and straightforward. Nonetheless, in certain cases, you might encounter boards in red, white, blue, yellow, and matte finishes. In even more exceptional instances, colors like black, purple, and bright green may appear. Generally, white PCBs are used for light applications. Other colors often denote product grading systems that vary by company. For example, some companies use red to signify experimental boards, blue for key boards, and black for internal panels used in computers. Each organization has its own conventions, which are not always comprehensively documented.
1. The most common color for PCB boards is green, often referred to as green board or green oil. The green solder mask is the oldest, most affordable, and widely used option. Generally, all electronic board-level products undergo processes for board fabrication and post-film applications. During the board-making process, several steps must be performed in a yellow light room. The visual effect of green under yellow light is advantageous, but this is not the main factor. During SMT soldering, the processes of tinning, post-film application, and final AOI verification are essential. These steps require optical positioning and calibration, and the green background color enhances instrument recognition.
2. Other common colors include red, yellow, blue, and black. Due to process limitations, many line inspections still depend on manual visual checks (although most now utilize flying probe testing). Maintaining focus while inspecting can be tiring. Green is relatively easier on the eyes, which is why it is predominantly used.
3. Blue and black PCBs contain cobalt and carbon, respectively, which introduce certain conductivity and increase the risk of short circuits. In contrast, green PCBs are more environmentally friendly and do not emit toxic gases when exposed to high temperatures.
4. In fact, darker colors can complicate the inspection and maintenance of the motherboard. For example, black PCB substrates are particularly prone to chromatic aberration during washing. If there are slight variations in the raw materials or processes used at the PCB factory, the defect rate may increase due to these color discrepancies. The circuit traces on black PCBs can be challenging to identify, making maintenance and debugging more difficult. Consequently, most motherboard manufacturers avoid using black PCBs. Even in high-quality applications like military and industrial products, green PCB substrates are preferred.
5. So, what impact does the color of the solder mask ink have on the board? While the ink does not affect the finished product, it significantly influences the semi-finished product, particularly in terms of manufacturing difficulty. Some may argue that color does affect the PCB board. Indeed, variations in green—such as matte green, sun green, dark green, and light green—can present challenges. A very light color may make plugs visible, resulting in an unappealing board appearance after the hole process, while overly dark colors can lead to issues like bubbles if the resin-to-dye ratio is incorrect. Variations in ink can lead to slight color changes, which might go unnoticed without extensive experience.
6. Although ink color does not impact board performance, ink thickness greatly affects impedance, especially for gold-plated boards, where strict thickness requirements are crucial. Experience shows that red ink, due to its cost and quality, is easier to control regarding bubbles and thickness. This color also conceals blemishes in the circuit better than green. Additionally, in the imaging process, several large PCB manufacturers have noted that red and yellow inks provide more stable exposure, whereas green can be inconsistent, and white is the hardest to manage. There are many other minor details in the solder mask process; some issues may not appear for years or can seem inexplicable upon first encounter.
7. In summary, while color does not influence the performance of the motherboard and does not play a decisive role in PCB design, every detail in the PCB design and production processes must be strictly controlled. The color of the PCB is primarily a marketing consideration. Therefore, it is not advisable for users to base their motherboard purchasing decisions solely on PCB color.
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