The color of a PCB typically refers to the hue of the solder mask on the board’s surface. PCB board staining pigments are a type of hardened resin, with the primary resin being colorless or nearly transparent. Green, as with other colors, is achieved through the addition of pigments.

We employ silk-screen printing to apply colors onto the PCB. PCBs come in various colors such as green, black, blue, yellow, purple, red, and brown. Some manufacturers have ingeniously developed PCBs in multiple colors like white and pink.

Physical Properties of PCB Colors

When selecting a PCB color, one must consider the physical properties of the PCB material. Typically composed of fiberglass and epoxy resin, PCB materials have densities, thermal conductivity coefficients, coefficients of thermal expansion, tensile strengths, and other physical attributes that directly impact performance and reliability. Different-colored PCBs may utilize varied production processes and materials, thereby exhibiting differing physical properties.

Chemical Properties of PCB Colors

In addition to physical properties, the color of a PCB also influences its chemical characteristics. PCB boards undergo heating and chemical treatments during production, and PCBs of different colors may require distinct chemical processes. This affects properties such as annealing temperature, acid and alkali resistance, and corrosion resistance. Some colored PCBs may employ more complex production processes and materials, resulting in enhanced chemical corrosion resistance.

Yellow PCB

Characteristics of Different Colored PCBs

  1. Green PCB

Green PCBs are the most popular color choice, enhancing clarity by providing a sharp contrast with white text, thus improving readability. Additionally, the surface treatment of green PCBs reflects less light, aiding in reducing glare.

  1. White PCB

White PCBs present a clean and neat appearance in various settings, gaining popularity. However, due to their tendency to obscure traces, white PCBs are not the top choice. Yet, the contrast with black silk-screen printing is notably distinct on white PCBs.

  1. Yellow PCB

Yellow PCBs cater swiftly to diverse requirements such as style, cleanliness, and visibility. However, a significant drawback of yellow PCBs is their poor contrast with traces and silk-screen printing.

  1. Blue PCB

Blue PCBs are considered thick boards suitable for labeling due to their significant contrast in silk-screen printing. While not as attention-grabbing as green, black, or white PCBs, blue PCBs are preferred for their excellent aesthetic appeal. Installing blue PCBs on LCDs is preferable as they avoid sharp contrast edges and bright background colors.

  1. Red PCB

Due to its advantages, many PCB manufacturers are keen on adopting red PCBs. Red PCBs offer excellent visibility and clearly define the contrast of traces, planes, and blank areas. Silk-screen printing appears particularly elegant against the backdrop of red PCBs.

  1. Black PCB

Black PCBs are as popular as white PCBs. Both colors produce low contrast, facilitating easy labeling of critical components. However, the primary drawbacks of black and white PCBs are the potential focal points and minor shadows, making tracing difficult. Therefore, black PCBs are unsuitable for various high-temperature applications as they may cause silk-screen printing to discolor. Moreover, black PCBs are a blend of cobalt and carbon, potentially resulting in poor conductivity.

Black PCB

How pcb colors are made

The color of a PCB (Printed Circuit Board) is primarily achieved by applying a layer of special solder mask during the manufacturing process. Here are the general steps involved in producing PCB colors:

  1. During the manufacturing process of a PCB, a thin layer of copper foil is first laid on the substrate, forming the conductive layer of the PCB. If producing a double-sided or multilayer board, both sides or multiple layers of the PCB substrate will be covered with copper foil.

  2. Next, the designed PCB circuit pattern is “printed” onto the metal conductor using a technique called subtractive transfer. In this process, the entire surface is covered with a layer of copper foil, and excess copper foil is removed through etching techniques to form the desired circuit pattern.

  3. After forming the circuit pattern, to separate the soldering and non-soldering parts of the PCB during soldering and prevent copper oxidation (pure copper surfaces quickly undergo oxidation reactions when exposed to air, and oxidized copper becomes a poor conductor of electricity, greatly damaging the electrical performance of the entire PCB), engineers apply a layer of solder mask on the surface of the PCB. This solder mask layer blocks the contact between copper and air, protecting the copper layer from oxidation.

  4. The color of the solder mask can be adjusted as needed. Since small text needs to be printed on the PCB, engineers typically add various colors to the solder mask to create different PCB colors. For example, black, red, blue, dark green, and dark brown are common PCB colors.

  5. After applying the solder mask, a series of post-processing steps such as hot air leveling, milling the outline, electrical testing, final inspection, etc., are required to ensure that the quality and performance of the PCB meet the requirements.

Why are most PCB green now?

The prevalence of green PCBs stems from several factors:

  1. Glass Epoxy Resin Material:

    • Historically, green was the standard color for the solder mask made from glass epoxy resin, which is commonly used in PCB manufacturing. While other colors have been introduced, green remains the preferred choice.

  2. Contrast with White Printed Text:

    • Green PCBs offer simplicity and time efficiency for assembly workers, as scanning them is straightforward and quick due to their familiarity with the color. Additionally, green creates less eye strain during scanning compared to other colors and provides contrast with white printed text on the circuit board.

  3. Military Applications:

    • Military standards have a significant influence on the preference for green PCBs. Many believe that green is highly effective for military purposes, leading to a demand for green PCBs from suppliers who also serve other clients. Consequently, green PCBs become surplus products for military suppliers, further reinforcing their acceptance.

  4. Exposure Rate of Solder Mask:

    • While other colors like blue, white, or brown exist, they may not offer a higher solder mask exposure rate compared to green. Darker colors tend to have higher pigment deposition, resulting in darker solder masks. White and black solder masks have high exposure rates, but green provides adequate shading for worker exposure and design tolerances.

  5. Better Machine Recognition:

    • During PCB manufacturing processes such as board fabrication and surface-mount component soldering, visual inspection is crucial. Green PCBs offer better visibility in yellow-lit environments, aiding machine recognition and calibration for tasks like solder paste application and automated optical inspection (AOI).

  6. Comfort for Workers:

    • In some manual inspection processes (although increasingly replaced by automated testing), workers may observe PCBs under strong lighting. Green PCBs are more comfortable for the eyes in such conditions.

  7. Cost Reduction:

    • Green PCBs have widespread use, enabling economies of scale in production and procurement. Standardizing on one color reduces production line costs, as bulk purchasing of the same-color solder mask lowers procurement costs. Consequently, green solder mask is advantageous in terms of manufacturing costs and lead times.

  8. Relative Environmental Friendliness:

    • Green PCBs are relatively environmentally friendly, as they do not release toxic gases during high-temperature recycling of waste boards. Other PCB colors, such as blue and black, contain cobalt and carbon, which pose risks of short circuits due to weaker conductivity.

Additionally, darker-colored PCBs, such as those in black, purple, or blue, may increase difficulty in board inspection and present challenges in manufacturing control.

The influence of PCB color on circuit boards is multifaceted. It affects not only the cost and appearance of the PCB but also directly impacts the physical and chemical properties of the PCB materials, thereby influencing the performance and reliability of the PCB. Therefore, when selecting PCB colors, it is necessary to consider a comprehensive range of factors such as the application environment, requirements, and costs of the product. Meanwhile, manufacturers need to enhance the quality and performance of PCBs through more sophisticated production processes and materials to meet the production needs of PCBs in different colors.