PCB Silkscreen – What Is It? Miracle Electronics

1. PCB Silkscreen – What Is It? A PCB has all sorts of tiny metallic components, white scribbles, and more on it. While the metallic components are used to conduct charge throughout the PCB, the white scribbles are what form the PCB silkscreen. It is a layer of white ink traces used to identify components, warning symbols, test points, logos, marks, etc. Applied on the component side, the silkscreen can help every manufacturer and engineer to locate and identify all the components on the board easily. It in fact acts like an instruction manual, telling the workers how to assemble the board as part of a larger device, while also communicating the function of every pin. The ink used in a silkscreen is a non-conductive epoxy ink that is highly formulated. Most commonly seen in white, the ink may also be black or yellow. The white ink is most preferred because it is easy to see against the green soldermask. However, yellow, black, red, gray, and blue silkscreens are also seen. How is silkscreen applied? Silkscreen is the last layer applied onto a PCB in the fabrication process, which can be applied in various ways – manual, liquid photo imaging, or direct legend printing. Manual application – When the line widths are greater than 7mil and the registration tolerance is 5mil, manual application is done. Here, a stencil of the text and traces made of nylon are required. The ink is pushed through the stencil on to the laminate, after which the board is

2. baked in a curing oven to let the ink cure. While the setup and application for such a process is easy, the result is not very effective. Liquid Photo Imaging – When the line widths are at least 4mil, this method is used. Here, a liquid photo-imageable epoxy is coated onto the laminate, which is then exposed to UV light. The board is then developed and cured, making the results more accurate than manual screening. Direct Legend Printing – In this process, an inkjet projector is used to apply acrylic ink onto the raw PCB directly from the CAD data, which is then cured with UV light as it is printed. This is the most accurate process of all, and is also comparatively more expensive. No matter what process you choose to have your PCB finished with, but there are certain considerations that you need to bear in mind regarding silkscreening. The silkscreen epoxy should not be printed over pads or land PCBs that will be soldered. Doing so will melt the epoxy into the solder joint. This is the reason epoxy is applied over the solder mask. Another important point to keep in mind is that you must keep the component outlines away from the pins, at least at a distance of 0.25mm. Also, keep the line widths above 6mil. Other than these two points, there is a lot more that one needs to consider while designing and applying a silkscreen on to a PCB. To keep yourself away from all these hassles, it is suggested that you leave the responsibility to a reliable and experienced PCB assembly manufacturer from Germany, one like Miracle Electronics. ALSO READ: 4 Guidelines To Choose The Right PCB Manufacturer