Solder mask is typically applied as an epoxy ink printed onto each side of a circuit board. This protects the copper surface and prevents solder bridges between components during assembly.
While the provided context is brief, a more detailed explanation of the solder mask application process generally involves these steps:
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Cleaning and Preparation: The circuit board panel is first cleaned to remove any contaminants that could affect adhesion of the solder mask.
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Application of Solder Mask: The solder mask, typically an epoxy-based ink, can be applied in several ways:
- Screen Printing: This is a common method where the solder mask is applied through a stencil (screen) onto the board.
- Spray Coating: The solder mask is sprayed onto the board. This is often used for irregular surfaces.
- Curtain Coating: The board passes through a "curtain" of solder mask material.
- Photoimageable Solder Mask (LPI - Liquid Photo Imageable): This method provides higher accuracy. The entire board is coated with a photo-sensitive solder mask. A UV light is then used with a mask/film to expose the areas of the board where the solder mask is desired. The unexposed solder mask is then washed away, leaving the solder mask only in the intended areas.
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UV Curing: After application, the solder mask is typically cured using ultraviolet (UV) light or thermal curing to harden the ink and ensure proper adhesion.
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Inspection: The board is inspected to ensure the solder mask is applied correctly and that there are no defects.
The choice of application method depends on factors such as the desired accuracy, volume of production, and type of solder mask being used. Photoimageable solder mask generally offers the highest accuracy and is preferred for boards with fine pitch components.
