PCB Manufacturing Process : Legend Printing
The legend printing process prints all of the vital information on the board, such as manufacturer marks, company ID numbers, and warning labels. Two methods are mainly used in this process: Screen printing, also known as silkscreen, and DLP for Direct Legend Printing with an inkjet printer. It looks easy, but like every step of the PCB manufacturing process, it requires precision.
As with most stages of PCB manufacturing, the artwork from the GERBER file is essential in the process of printing the legend pattern. The first method is screen printing also known as silkscreen process. Whether manual or automatic, they both require polyester screens stretched across aluminum frames. Both the aluminum frames and the panel are registered to guarantee proper alignment to avoid print ink on the copper pattern and to ensure that the soldering process will not be affected. The ink is pushed through the stencil onto the laminate.
Once the PCB has been silk-screened with the correct information, visual inspection is carried out by the operator. In case of defect, the operator will assess the issue or remove the board from the production process
If the result of the screen printing is good, the boards will be cured to harden the ink.
The second process of applying the legend text works like a conventional inkjet printer and is knows as DLP or Direct Legend Printing. Registration is done automatically by the machine. The inkjet printer sprays ink droplets on the panel to generate the image. These ink droplets are directly cured by UV lights.
Visual control is also carried out by the operator to make sure the legend is correctly printed. Despite more modern equipment, DLP is preferable only for prototyping and small volumes while screen printing is much faster and used for mass production.