Silk screening is a crucial part of PCB manufacturing, and it is one of the final steps of the process. But what makes it so important? Why do companies use silkscreen? In short: What is the idea behind the process?
Here, we will explain everything you need to know about silkscreen and why it is such a pivotal part of the PCB design.
What Is Silkscreen?
Silkscreening is the process of adding a layer of ink on the print circuit board. Most commonly, PCB is green, but it can be any other color as well. One can print in any color, but manufacturers usually opt for something standard, like white, yellow, or black.
Furthermore, the silkscreen is usually on the side with components, but you can encounter PCBs with silkscreen layers on the solder side as well. The ink used in the process is non-conductive epoxy ink or acrylic ink.
It is worth mentioning that acrylic ink is not cured on PCBs with silver finishes. Moreover, printing always includes standard, easy-to-read fonts.
But why do companies print on PCBs? There are numerous reasons why this might be the case. Silkscreen printing is an important part of the process, and it can be beneficial for both engineers and manufacturers.
Let’s dive into the reasons why the silkscreen is so important for everyone using printed circuit boards (PCBs).
It Helps During Testing
Testing is one of the final stages of PCB manufacturing. Once the board is finished, the technician will proceed to perform electrical tests on various areas on the PCB. The testing serves to ensure that the circuit is operational and that there are no burnt parts or any other undesired results.
The printing on the board will allow technicians to easily navigate across the board and find test locations or points where they should perform measurements during the troubleshooting.
It will also inform the technician of the component type, part numbers, various processes like SnPb or RoHS. That can significantly help during the identification of the causes of potential failure.
Identification is the primary goal of silkscreening. IPC made a standard for all PCB manufacturers to place both their mark and identifier on the board. The goal here is to ensure effortless tracing in case of a mistake or any type of problem.
Identification on PCBs includes circuitry, testing points, component interconnects, ground points, checking whether there is a need for evaluation, part replacement, and so on.
It also helps authorities to verify if the product is according to standards and if it complies with the Restriction of Hazardous Substances. Moreover, it provides information about the company that designed the board, registration numbers, etc.
When it comes to maintenance, the person checking the board can easily recognize important components, board name, warning symbols, part number, voltage, etc. Silkscreening also provides practical information like polarity, orientation, logos, labels, and components.
Silkscreen works similar to legends on charts and maps. They let you see every bit of information that will help you with testing, maintaining, or using the printed circuit board. It is also a great way to label your products or versions of printed circuit boards.
Lowering the Possibility of Errors
The very idea behind PCB silkscreen is to make everything transparent. As a result, it will significantly lower the possibility of any type of error. Since nearly every bit of information is already printed on the board, it will make it unlikely that something will go wrong.
Moreover, the time needed to spot an error on the PCB will also be reduced since the technician won’t need to search for anything. As a result, a detailed PCB layout can save you both time and money in the process.
Of course, silkscreening won’t eliminate any mistakes that may occur in the process. However, it will significantly make it easier for technicians to spot them before it’s too late.
Safety and Comfort
A silkscreen layer will serve almost as a safety net since it will provide much useful information. The person in charge of the PCB assembly will have an easier time placing components in the right place using the identifiers.
A silkscreen will act as a visual feedback, and it can point to deeper potential problems. Furthermore, we already mentioned that it might include warning signs, and that can include high voltage, grounding, or any other parameter that should be treated with special care.
Consequently, it can help locate potential failure causes, making it an extra layer of safety for your printed circuit board.
Understanding Silkscreen Can Reduce Costs
Understanding how silkscreen works, studying different methods, and paying attention to details can also reduce the cost of PCB fabrication. The most obvious example is sticking to standard colors and designs. There is no reason to experiment with anything other than white, yellow, or black.
While it is possible to use any other color for your PCB, it can only increase the cost of production. Similarly, you should stick to silk screening on only one side of the PCB. That can be rather important since silk screening can contribute to nearly 15% of the cost of your PCB.
Moreover, the price of the process is based on the method of your choice. But, more on that later.
Branding and Recognition
Finally, you can use silkscreen to make your printed circuit board stand out from the crowd and be unique. Usually, companies will imprint their mark, name, or logo on the board, which will make it recognizable and serve almost as a certificate of quality.
Even though it is not the most important thing on the list, it can be a nice touch to the design of your PCB. However, branding your product is not just for bragging. It can serve a higher purpose as well.
Firstly, it will grant publicity for your company and your brand. More importantly, it can act as a protection against copyright infringement.
Today, there are three main ways to apply a silkscreen layer to your PCB. Each method can offer something different, and you can pick one based on your preferences regarding the price and accuracy.
1. Manual Screen Printing
The first method is manual screen-printing, and it is used when the line widths are greater than 7 mils or 0.007 inches, and when the registration tolerance is 5 mils. Manual screen-printing requires a stencil of the text you want to print on the board and traces that are usually made of nylon.
The ink is then pushed through the stencil directly on the laminate layer. Once the process is finished, the ink is cured in the oven. Using this method is one of the easiest methods of designing a silkscreen layer, and you can use it to create bigger text as well.
2. Liquid Photo Imaging (LPI)
The second method, that is, liquid photo imaging, is used for lines that are greater than 4 mils (0.004 inches). The LPI process is rather similar to the solder mask application. The solder mask is a thin layer of polymer similar to lacquer that gives the PCB recognizable green color.
The only difference is that LPI laminate is coated with epoxy. After the coating is complete, the board is placed under the UV light and cured. LPI allows higher precision compared to manual screen printing, and the letters are usually white.
It is worth mentioning that LPI also uses the most ink in comparison with the other two methods on the list.
3. Direct Legend Printing (DLP)
The third and final method is direct legend printing (or DLP). While it uses less ink than LPI, the process is a lot more expensive. Here, the inkjet projector will use acrylic ink, and it will apply it directly to the PCB using CAD software.
Similarly to LPI, the board is placed under the UV light as it is printed, and it is not suitable for PCBs with silver finishes. The reason why DLP is the most expensive of all three methods is accuracy — it is the most accurate method on the list.
The silkscreen is an important part of a printed circuit board (PCB). It is one of the final parts of the design process, and it can provide useful information for both engineers and manufacturers.
During the process, a layer of ink is added on the surface of the PCB using one of the three methods. The idea behind silkscreen is to provide valuable information about the PCB, components, manufacturer, purpose, and others.
The information on the PCB can significantly aid the troubleshooting process, as well as during the PCB assembly. It will also lower the possibility of errors, and even if they do happen, locating the problem will be significantly easier.
Here, at MKTPCB, we have years of experience helping our clients with every step of the PCB manufacturing process. So, feel free to contact us with any questions you might have about our products, processes, or anything else. We are here to help!