In the manufacturing process of printed circuit boards (PCBs), solder mask ink is a crucial material. It not only protects the PCB surface from environmental impacts, but also prevents solder bridging during the soldering process, ensuring the reliability and performance of the circuit.

Solder mask ink composition

Solder mask ink is a special polymer coating applied between the copper traces and pads of the PCB. Its main function is to prevent solder from flowing to unwanted areas during the soldering process, thereby avoiding short circuits and other electrical faults. Solder mask ink is usually composed of the following ingredients:
Resin: Provides the basic structure and mechanical strength of the ink.
Pigment: Gives the ink color, common colors are green, blue, red, etc.
Solvent: Used to adjust the viscosity and fluidity of the ink.
Additive: Improves the properties of the ink, such as adhesion, chemical resistance and heat resistance.

Function of solder mask ink

Protection function: Solder mask ink covers between the copper traces and pads of the PCB, forming a protective film to prevent oxidation, moisture and chemical corrosion. This protection function extends the service life of the PCB and improves its reliability.

Soldering aid: During the soldering process, solder mask ink restricts the flow of solder to prevent solder bridging and short circuits. It ensures that the solder is only attached to the pad, thereby improving the soldering quality and electrical performance.
Mechanical support: Solder resist ink provides certain mechanical support, enhances the structural strength of the PCB, and prevents mechanical damage during operation and use.
Insulation performance: Solder resist ink has good insulation performance, prevents electrical short circuits and leakage, and ensures the safety and stability of the circuit.

Types of solder resist inks

Thermosetting inks: Thermosetting inks are cured by heating to form a strong coating. It has excellent heat resistance and mechanical strength and is suitable for high-temperature soldering processes.

UV-curable inks: UV-curable inks are cured by ultraviolet light irradiation, with a fast curing speed and are suitable for mass production. It has good chemical resistance and adhesion, but relatively low heat resistance.
Photosensitive inks: Photosensitive inks are cured by chemical reaction after exposure and are suitable for PCB manufacturing with fine lines. It has high resolution and is suitable for high-density interconnect (HDI) boards.

Selection and use of solder resist inks

1. Selection factors

The following factors need to be considered when selecting suitable solder resist inks:
Process requirements: Select the appropriate ink type according to the manufacturing process of the PCB, such as thermal curing, UV curing or photosensitive inks.
Environmental conditions: Consider the use environment of the PCB, such as temperature, humidity and chemical corrosion, and select inks with corresponding resistance.
Color requirements: Select the appropriate ink color according to the design requirements of the product. Common colors include green, blue, red, etc.
Cost factor: Choose ink with high cost performance under the premise of meeting performance requirements.

2. Precautions for use
When using solder mask ink, you need to pay attention to the following points:
Surface treatment: Ensure that the PCB surface is clean, free of oil and oxide to improve the adhesion of the ink.
Uniform coating: Ensure that the ink is evenly coated to avoid defects such as bubbles and pinholes.
Curing conditions: Strictly control the curing temperature and time to ensure that the ink is completely cured to achieve the best performance.
Quality inspection: Perform quality inspection after the ink is cured to ensure that the thickness, adhesion and insulation performance of the coating meet the requirements.

From a process perspective, the application of PCB solder mask ink requires a high degree of precision and consistency. During the coating process, screen printing, spraying or rolling methods are usually used to evenly cover the ink on the PCB surface, and after a series of complex processes such as pre-curing, exposure, and development, a solder mask layer with precise graphics and good adhesion is finally formed. Each link places strict requirements on the performance of the ink and the technical level of the operator. For example, the exposure process requires precise control of exposure time and intensity to ensure that the ink can be cured according to the designed pattern under the action of ultraviolet rays. The development process must ensure that the uncured ink can be thoroughly cleaned, otherwise it will affect the quality and reliability of the PCB.