What is a Liquid Photo-Imageable Solder Mask?

Printed circuit boards have broken away from their uniform green coloration thanks to liquid photo-imageable solder mask, which you may see referred to as LPI or LPISM in different industry publications. This is essentially a specialty ink that can be screen printed, sprayed or curtain coated on PCBs and other items.


By using a mixture of polymers and coating solvents, liquid photo-imageable solder masks achieve a thin coating that works for nearly every PCB surface, making it an effective replacement for traditional PCB coatings. It is cured on the board with a UV light after the panel is cleaned and scrubbed.



Green solder mask

most commonly used color for PCBs. It is popular because it provides good contrast for white silkscreen printing and it is easy to manufacture. The green color is achieved by using liquid photo imageable solder mask (LPI) that contains a green pigment. This pigment absorbs UV light during the exposure process, which results in the green color. Green has been used for many years in PCB manufacturing, and it is a recognizable color used by engineers and PCB enthusiasts.

White solder mask

another popular color used for PCBs. It provides good contrast for black silkscreen printing and it gives a modern, clean look to the board. White solder mask is also achieved by using LPI with a white pigment. However, white pigment is less opaque than green, so it may require multiple coats to achieve the desired coverage. Some PCB manufacturers offer matte white solder mask, which has a matte finish and can reduce reflections on the board’s surface. Overall, white solder mask is a good option for PCBs that require a clean, modern look with good contrast for silkscreen printing.

Black solder mask

is a color option for printed circuit boards that offers a sleek and modern look. It is the least common color used for solder mask but has gained popularity in recent years, especially for high-end applications that require a more sophisticated appearance. Black solder mask is typically achieved by adding a black pigment to a liquid photo imageable (LPI) material used for the solder mask layer. Black solder mask can provide better contrast for white silkscreen printing and can make copper traces and components stand out. However, it can also pose challenges during inspection and testing due to its dark color. Overall, black solder mask is a good option for PCBs that require a high-quality, professional look with good contrast for silkscreen printing.

Red solder mask is a popular color choice for printed circuit boards since it provides good contrast for silkscreen printing, making component identification easier. It is commonly used in automotive, aerospace, and medical industries to indicate critical components or to enhance the design of the board. The red color is achieved by adding a red pigment to the liquid photo imageable (LPI) material used for the solder mask layer. Red solder mask can also make PCBs more visible, which can be helpful in applications where the board needs to be easily identifiable or where safety is a concern. However, like any other color, red solder mask can also pose challenges during inspection and testing. It is important to select the appropriate color based on the application requirements and the equipment used for testing and assembly. Overall, red solder mask is a good choice for PCBs that need to be easily identified and require a professional and sophisticated appearance.

Blue solder mask is a type of protective coating applied to a printed circuit board (PCB) to protect the copper traces from damage and to insulate the board. The blue color is just one option for the solder mask, as it can also be green, red, yellow, or any other color. The solder mask is applied before the board is populated with components and is typically made from a heat-resistant, epoxy-based material that can withstand the high temperatures needed for soldering.

Yellow solder mask is another type of protective coating applied to a PCB to protect the copper traces from damage and to insulate the board. As with blue solder mask, the yellow color is just one option among many.
Other than blue and yellow, common colors for solder mask in PCBs include green and red. Green is often associated with PCBs because it was the original color used by the earliest PCBs in the 1950s and 1960s. Red is also a popular option for solder mask, as it can enhance the visibility of traces and components, making inspection and testing easier.

In addition to color, solder mask can differ in its composition, thickness, and other properties. Some solder masks, for example, may be harder or softer than others, or may be more or less resistant to abrasion, chemicals, or UV light. The specific solder mask used in a given PCB will depend on factors such as the intended operating environment and the requirements of the application.


Matte and glossy solder mask are two types of finishes that can be applied to printed circuit boards (PCBs) to protect the copper traces from oxidation and prevent solder bridges during assembly.

Matte solder mask has a rough, non-reflective surface finish that diffuses light and reduces glare. It is typically used in applications where light reflection and visual appearance are not important, such as industrial control systems or automotive electronics. The rough surface also provides a better grip for SMT components during assembly.

In contrast, glossy solder mask has a smooth, reflective surface finish that enhances the contrast and color of the underlying copper features. It is often used in applications where visual appearance is important, such as consumer electronics or high-end audio equipment.

From a technical standpoint, there is no significant difference between matte and glossy solder mask in terms of their electrical or mechanical properties. The choice between the two finishes comes down to the designer’s aesthetic preferences, the intended use of the PCB, and any branding or marketing considerations.