Legend printing ,also known as Silkscreen, is a process of printing informational texts or patterns on the surface of the board. Legend information includes component reference designators, switch settings, test points, part numbers, version numbers, company logos, or some other pattern to beautify the appearance. While printing legend, two methods are mainly used: screen printing and direct legend printing (DLP)
Screen printing is based on the principle that the mesh of the graphic part of the screen is permeable to ink while the non-graphic part of the screen is not. In the legend printing process, a screen for printing is first produced according to the legend film. The ink then penetrates through the mesh of the screen under pressure and thus is printed on the surface of the board. Finally, the board is baked in an oven at a high temperature to ensure that the legend ink is well attached to the circuit board.
In addition to screen printing, DLP is another method of printing legends. Direct Legend Printing (DLP) uses electronic inkjet printing technology to print the information obtained from CAD/CAM files onto circuit boards with specific ink and then cure the ink timely through ultraviolet lamps to complete the legend process. Compared with traditional screen printing, legend printing technology has higher printing accuracy and spares the use of films, but this process is preferable only for small batches of sample printing. Screen printing, on the other hand, can be used for mass production and is an easy and relatively inexpensive process.
Although from the perspective of electrical characteristics, the absence of legend information does not affect the performance of the circuit, it has a good indication for assembly and maintenance of the board. The colors of ink are usually black or white, but PCBWay also offers yellow or other colors depending on the user's design requirements. In order to make all the letters, numbers, and symbols printed on the board easy to identify, PCBWay’s manufacturing capability requires that the width and the height of the legend that must be at least 0.15mm and 0.8mm respectively.
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