PCB Reliability
A PCB’s solder mask defines the area that is covered by copper traces and pads, protecting the underlying components from short circuits caused by incorrect connections. The mask also prevents bridging and shorts by delimiting the flow of solder across different areas on the board, thus keeping them separate. The solder mask also protects the underlying copper from chemical degradation and environmental exposure.
However, the reliability of a solder mask depends on multiple factors, including how it is applied, the type and manufacturer of the material used to create it, and the curing conditions used during application and cure. In addition, the environmental conditions that affect its chemical and thermomechanical properties must be considered.
Solder masks are made up of a complex mixture of materials that determines how well it adheres to the surface of the PCB and how well it cures into a thin, protective layer. They are typically made from photoreactive resins/binders, crosslinking resins, fillers, pigments, surfactants, and solvents that have been combined and structured to create a thin film for application to the pcba. The precise combination and formulation of these materials is determined by the manufacturing process that will be used to apply the mask, the coating and curing parameters that are specified by the PCB design rules, and the environmental conditions that the solder mask will be exposed to during production.
Some of the most common functions of a solder mask include preventing polarity violations, shorts and bridging between copper traces and pads, and coating the surface of plated holes (vias) with an insulation layer to prevent wicking which can lead to solder bridges. The mask can also be structured to provide space for machine-readable markings and labels to allow easy identification of the PCB’s parts, features, and functions.
Solder Masks and PCB Reliability
Insufficient or inappropriate curing of the mask can result in delamination, a process whereby the mask separates from the underlying copper and exposes the pads and traces to contamination and other potential problems. This can occur due to a number of factors, including insufficient or improper surface preparation and curing and temperature/pressure variations during the manufacturing process.
Solder masks can be cured using various energy sources, from UV to heat and pressure, depending on the type of material used to make it. The most reliable methods involve exposing the mask to energy at the correct wavelength and for the required time.
While the most common colors for a PCB’s solder mask are green and black, they can be printed in other shades to suit design requirements or to match the color scheme of a company’s products. These other colors can be used to differentiate prototypes from final products or to satisfy other design requirements like giving a product a unique appearance.
Unlike silkscreen, which is limited to the color black and white, the solder mask can be any color. This is done to meet design requirements like identifying the prototype from the final product, or to match the color theme of an enclosure. NEXTPCB offers green, red, and blue solder masks, but we can also make custom colors for special projects.
