There are three main methods used for PCBA silkscreen printing. They are as follows:
Manual Screen Printing: As the name suggests, manual silk screen printing is done by hand. The task is performed with the help of a stencil comprising traces and texts made up of nylon. The non-conductive ink is evenly spread on the upper PCB layer through the stencil. After lamination, the ink is dried in a baking oven. The Manual screen printing method is the most cost-effective and simple. It is specially used for PCBs whose registration tolerance is 0.005.
Direct Legend Printing: This is one of the most expensive and accurate methods of printing silkscreen. Direct legend printing, or DLP, is done using inkjet projectors and acrylic ink. The ink is applied on a printed circuit board using CAD software. This process can be used for PCBs that do not contain a silver finish because acrylic ink is not suitable for the same.
Liquid Photo Imaging of Silkscreen: This printing method is used on a PCB with a width of fewer than four millimeters. Firstly, the lamination is done using light-sensitive epoxy. Once the silkscreen image is printed, it is then exposed to UV light.