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What is the meaning of soldermask in PCB? What is its function?

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Solder Resist is a layer of material used to protect circuits and provide insulation in a PCB. It is usually composed of a layer of special ink or resin material, covered in the PCB board in addition to the pads, conductive paths and need to be soldered in addition to the area of all the copper surface. The main functions of the soldermask layer include:

Prevent Soldering Short Circuit: 

Soldermask can prevent the soldering process in the solder bridging different conductive paths, thus avoiding short circuits.

Protection of Circuits: 

Soldermask can protect the copper wires and pads on the PCB board from mechanical damage, chemical corrosion or environmental factors, to extend the life of the PCB.

Provide Insulation: 

Soldermask acts as an insulating material to prevent electrical shorts between neighbouring conductors on the board.

Improves Solderability: 

Soldermask provides a clearer and more controlled soldering area, helping to improve solder quality and solderability.

Aesthetics: 

Soldermask is usually available in green or other colours and can cover the yellow or brown colour of copper, making PCBs look neater and more professional.

Auxiliary Silkscreen: 

The soldermask layer can be used as a base for the silkscreen layer, and logos and patterns on the silkscreen layer can be displayed more clearly on the soldermask layer.

Material Selection for Soldermask

Materials for soldermask usually include the following:

Epoxy Resin: 

This is the most common soldermask material, with good chemical resistance and mechanical strength, suitable for a variety of PCB manufacturing processes.

Polyimide (PI): 

This material has excellent high-temperature resistance and is suitable for PCBs in high-frequency or high-temperature operating environments.

Polyester (PET): 

polyester materials are lower cost, but heat resistance and chemical stability is relatively poor, suitable for some low requirements of the application.

Light-cured Soldermask: 

This type of soldermask is cured by UV light and provides higher precision and better surface flatness.

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Soldermask Colours and Applications

In addition to green, the soldermask can be other colours such as blue, red, yellow or black. The choice of colour is mainly based on the aesthetic requirements of the end product and the readability of the silkscreen. For example, black soldermask provides better contrast in some cases, making the silkscreen logo more legible.

Thickness of Soldermask

The thickness of the soldermask is also an important parameter, usually between 0.1 and 0.2 mm. A too thin soldermask may not provide sufficient protection, while a too thick soldermask may cause soldering problems or affect the performance of the circuit.

Openings in The Soldermask

Soldermask has windows of certain shapes and sizes that are required by the design for component soldering, test point access, or circuit connections. These openings must correspond precisely to the pads and conductive paths on the PCB to ensure smooth assembly and repair.

Quality Control of Soldermask

Quality control of the soldermask is critical during the PCB manufacturing process. It is necessary to ensure that the soldermask layer is free of bubbles, cracks, flaking and other problems, and that it is uniform during the curing process to ensure the performance and reliability of the soldermask layer.

Through comprehensive consideration of the above factors, the design and application of soldermask can significantly improve the overall quality and performance of the PCB, ensuring the reliability and durability of electronic products.

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