A PCB solder mask is commonly made of epoxy liquid.
Solder mask serves as a protective layer on a printed circuit board (PCB), shielding the copper traces from oxidation, and preventing solder bridges during assembly. While various materials can be used, epoxy-based materials are the most prevalent due to their cost-effectiveness and reliable protection.
Here's a breakdown of common solder mask materials:
- Epoxy: This is the most common type. It provides good chemical resistance, electrical insulation, and is relatively inexpensive. Epoxy solder masks are usually applied as a liquid and then cured with UV light or heat.
- Liquid Photoimageable (LPI) Solder Masks: These are more precise and allow for finer feature sizes. They are applied as a liquid and then exposed to UV light through a phototool (a film with the desired pattern). The exposed areas harden, while the unexposed areas are washed away, leaving the solder mask pattern. LPI solder masks offer better resolution and registration than epoxy.
- Dry Film Solder Masks: These are applied as a solid film to the PCB. Like LPI masks, they require a phototool and UV exposure. They offer excellent resolution and are suitable for high-density PCBs.
- Other materials: While less common, other materials like acrylics and polyurethanes can also be used for solder masks, each offering different properties and advantages.
The specific type of epoxy or other material used will vary depending on the manufacturer and the desired performance characteristics of the PCB. Key properties include:
- Dielectric strength: Ability to withstand high voltages.
- Adhesion: How well the mask adheres to the copper and substrate.
- Chemical resistance: Resistance to chemicals used in PCB fabrication and assembly.
- Thermal resistance: Ability to withstand high temperatures during soldering.
- Resolution: Ability to create fine lines and spaces.
In summary, while different materials exist for solder masks, epoxy is the most frequently used due to its balance of cost and performance. Liquid Photoimageable (LPI) solder masks are also quite common for more precise applications.
