Silkscreen on a PCB: What is it?

A printed circuit board is considered one of the crucial components of modern electronic systems. PCB is a flat board made of insulating material, such as fiberglass or plastic, that supports and connects the various components of an electronic circuit. A PCB typically has several layers, each of which serves a specific function in the circuit.

One of these layers is the silkscreen, also known as the silk layer. This layer of print on the PCB board has information about the circuit and its components, such as PCB components, marks, logos, symbols, etc. When the manufacturer completes the PCB design process, silkscreen is typically applied on top of the other layers of the PCB board, and it is used as a reference for assembling and troubleshooting the circuit.

Some of the key advantages of silkscreen are that it makes it easier to assemble and troubleshoot the circuit. For example, when assembling the PCB, the silkscreen can be used as a guide to help identify the correct location for each component. Similarly, when troubleshooting the circuit, the silkscreen can quickly identify the different components and their values, which can help diagnose the problem.

What is a silkscreen on a PCB?

The silkscreen is a layer of ink traces that typically includes labels for the various components on the PCB, such as the names of the connectors and the values of resistors and capacitors. It may also include other information, such as the PCB's title, the polarity of parts, and the test point locations. The silkscreen is applied to the component part of the printed circuit board.

Silkscreen layer onto the PCB surface with components placed

In addition to its practical benefits, the silkscreen also serves a visual function. It can add branding, company logos, and other decorative elements to the PCB, making the final product more attractive and professional-looking. The ink used for the silkscreen layer is a non-conductive epoxy ink with several colors, including black, white, red, blue, and yellow. 

Silkscreen is an important part of a board design, and it plays a crucial role in the design and function of electronic circuits. Whether you are an engineer designing a complex circuit or a hobbyist building a simple project, the silkscreen can help you assemble and troubleshoot your circuit more effectively.

What are the benefits of using silkscreen on a PCB?

 There are several benefits to using silkscreen on a PCB, including:

• Improved readability and clarity: The silkscreen provides labels and other information about the circuit and its components, which makes it easier to read and understand the PCB.

• Easier assembly and troubleshooting: The silkscreen can be used as a reference for assembling and troubleshooting the circuit, saving time and effort.

• Enhanced aesthetics: The silkscreen can be used to add branding, logos, and other decorative elements to the PCB, which can improve the appearance of the final product.

• Improved durability: The silkscreen is applied on top of the other layers of the PCB, which means it is less likely to be damaged or worn away over time.

Design considerations for PCB silkscreen

Several design considerations should be considered when designing the silkscreen for a PCB. These include:

• Size and placement: The silkscreen should be large enough to be easily readable but not so large that it takes up too much space on the PCB. It should also be placed where it is easily visible and does not interfere with the other components on the PCB.

• Font and style: The silkscreen font and style should be clear, easy to read, and consistent throughout the PCB. Avoid using overly ornate or complex fonts, as these can be difficult to read.

• Color: The color of the silkscreen should be chosen carefully. Dark colors, such as black or dark blue, are typically the easiest to read, but they may not be suitable for all applications.

• Information: The silkscreen should include only essential information about the circuit and its components. Avoid including unnecessary details or information already provided elsewhere on the PCB.

Methods for creating silkscreen

There are several methods for silkscreen printing on a PCB, including:

• Screen printing: This is the most common method for creating the silkscreen on a PCB. It involves using a fine mesh screen to transfer the print onto the PCB. The screen is coated with a layer of photosensitive emulsion, which is then exposed to light through a film positive of the silkscreen design. The emulsion is then washed away, leaving a design stencil on the screen. The ink is then applied to the screen, passing through the stencil onto the PCB.

• Inkjet printing: This method uses an inkjet printer to print the silkscreen directly onto the PCB. The printer is equipped with a special printhead that can print on the surface of the PCB.

• Laser printing: This method uses a laser to etch the silkscreen onto the PCB. The laser is guided by a computer-generated design, which burns away the PCB's surface to create the silkscreen.    

Manual screen printing

Manual screen printing is a method of printing in which a fine mesh screen is used to transfer the print onto the surface of a PCB. The process involves coating the screen with a layer of photosensitive emulsion, exposing it to light through a film positive of the design, and then washing away the emulsion to create a stencil of the design on the screen. Ink is then applied to the screen, passing through the stencil onto the surface to be printed.

Manual screen printing in process

Manual screen printing is a popular method for creating high-quality prints on various surfaces. It is often used for creating silkscreen on a PCB. Unlike automated printing methods, manual screen printing allows for more control over the printing process and can produce prints with finer detail and better resolution.

Liquid Photo Imaging (LPI)

Liquid photo imaging, also known as LPI, is a silkscreen printing method that is very similar to the process used for applying solder masks and used when the line widths are greater than 4mm. The process of LPI begins by coating the screen with a layer of liquid photo-imageable epoxy (laminate with epoxy). The emulsion is then exposed to UV light, which is then developed and cured. This method is considered to have better accuracy than manual screen printing, but LPI uses more ink than any other method.

LPI has several advantages over traditional screen-printing methods. It produces prints with higher resolution and better detail, allowing for more precise control over the printing process. However, LPI takes more time to set up than traditional screen printing, which makes it a complex process for high-volume silkscreen PCB operations.

Direct Legend Printing (DLP)

Direct legend printing is a method of silkscreen printing on a PCB that involves printing the legend directly onto the PCB using CAD software tools. In this method, the legend is printed onto the PCB using a particular inkjet printer, and acrylic inks are used. The inkjet printer is equipped with a printhead that can print on the surface of the PCB.

Direct legend printing has several advantages over traditional screen-printing methods. It is considered to be one of the most expensive methods of printing silkscreen onto a PCB. Additionally, it produces prints with higher resolution and better detail, which makes it ideal for creating high-quality PCBs.

One of the critical challenges of direct legend printing is that it is unsuitable for all PCBs. In particular, it is not well-suited to PCBs with complex designs or multiple layers, as the printhead may not reach all areas of the PCB. Additionally, the ink used in direct legend printing may not be as durable as the ink used in traditional screen printing, which means that the legend may be more susceptible to wear and damage over time.

Key Takeaways

1. The silkscreen on a PCB is an essential layer of print that provides important information about the circuit and its components. 

2. It is used as a reference for assembling and troubleshooting the circuit. 

3. The silkscreen can also add branding, logos, and other decorative elements to the PCB.

4. Several methods exist for creating silkscreen on a PCB, including manual screen printing, liquid photo imaging, and direct legend printing. 

5. The silkscreen is an essential part of a PCB, and it plays a crucial role in the design and function of electronic circuits. 

6. Whether you are an engineer designing a complex circuit or a hobbyist building a simple project, the silkscreen can help you assemble and troubleshoot your circuit more effectively.

References

[1] https://resources.altium.com/p/your-guide-pcb-silkscreen 

[2] T. Yan and M. D. F. Wong, "Recent research development in PCB layout," 2010 IEEE/ACM International Conference on Computer-Aided Design (ICCAD), 2010, pp. 398-403, doi: 10.1109/ICCAD.2010.5654190. 

[3] A. Toprak and A. R. Boynuegri, "Printed Circuit Board Rapid Prototyping with Three-Dimensional Printer," 2020 4th International Symposium on Multidisciplinary Studies and Innovative Technologies (ISMSIT), 2020, pp. 1-7, doi: 10.1109/ISMSIT50672.2020.9254998.

[4] A. Toprak and A. R. Boynuegri, "Printed Circuit Board Rapid Prototyping with Three-Dimensional Printer," 2020 4th International Symposium on Multidisciplinary Studies and Innovative Technologies (ISMSIT), 2020, pp. 1-7, doi: 10.1109/ISMSIT50672.2020.9254998. 

[5] V. Anand, V. Singh and V. K. Ladwal, "Study on PCB Designing Problems and their Solutions," 2019 International Conference on Power Electronics, Control and Automation (ICPECA), 2019, pp. 1-5, doi: 10.1109/ICPECA47973.2019.8975402.