Functional 3D Inkjet Printing of Solder Mask
The traditional solder mask process is in danger. Digital inkjet processing has reached the point where it has become a viable option in the PCB manufacturing industry. Equipment for such an application has been around for a number of years with emphasis placed on printing legend or nomenclature on panels. However, the application of solder mask with the same type of equipment has shown real promise recently. New equipment such as the Camtek Gryphon, and processes are in the early stages of proving themselves as a viable alternative to the typical methods in use today. Equipment is now available that can support design issues related to:
- Multiple colors and finishes on a single panel
- Selective applications
- Inclusion of legend printing once the solder mask application has been completed
The implementation of this technology as part of the manufacturing process will bring with it a dramatic change to production capabilities and design specifications. The limitations surrounding registration of fine pitch relief, solder dams and BGAs will certainly be diminished. Current designs must take into consideration the inability of standard processing to consistently meet the decreasing space between copper features on the board. With the advent of using digital information instead of the traditional tooling, smaller and tighter registration may be accomplished on a consistent basis. A digital layout for the mask application would mean that areas that are meant to be free of coverage are never coated with ink. Using the typical expose and develop process the entire panel is coated and then the areas to remain covered are exposed to an ultraviolet source. The panels are then sent through a developing solution that should remove any unexposed ink. Removing the ink left behind in high aspect ratio via holes is very difficult if not impossible. Solder mask dams and tangent relief of pads is solely dependent on the accuracy of the current tooling systems. With a digital map of where the ink needs to be placed on the panel in direct relation to etched features the registration is not dependent on tolerance-limited tooling.
The potential benefits of a digital solder mask printing system for PCB assemblers, design engineers, and PCB manufacturers include;
- Significant savings in material usage;
- Higher resolution and registration accuracy;
- Equipment costs savings;
- Thinner and stronger solder dams;
- No solder mask residues inside holes;
- Selective thickness:
- Thicker on conductors,
- Thinner on laminate areas;
- Labor cost savings;
- Photo-tools cost savings;
- Lower chemical waste and waste treatment costs;
- Resistant solder mask materials with inherent flame retardant capability;
- Good adhesion of the ink to the substrate.
As an aside there can be environmental and cost savings for the PCB manufacturer with the changeover to an inkjet process for mask application. The basic 4 step process of flooding the panel with ink, exposing, developing and curing it is reduced to a 2 step process involving just application and cure; an obvious reduction in handling, chemistry, equipment costs, photo-tool creation & maintenance in addition to reduced rejects, returns and rework.
As seen in the image below, the steps to process a panel are dramatically less.
The design engineer no longer needs to worry about tolerances of solder mask for those tight jobs. The bottom line is that digital 3D inkjet processing of solder mask is a benefit to the design engineer, the PCB manufacturer, the PCB assembler and the overall quality of the final product.
Are you a design engineer or PCB assembler? We would love to hear your thoughts on how this technology changes the game when it comes to PCB design.