The Ultimate Guide to PCB Silkscreen: Process, Methods & More
Adding a silkscreen layer into a board is the last step in the PCB manufacturing process. The silkscreen is a layer that applies ink traces to detect PCB components, test points, warning symbols, logos, marks, etc. Manufacturers mainly use silkscreen on the component section. You can find it on the solder section on some rare occasions, though this method is a bit expensive. Basically, a PCB silkscreen helps manufacturers and designers to identify components quickly.
The silkscreen ink is a non-conductive epoxy ink and is highly formulated. While silkscreens come in different colors, there are three common colors in the PCB manufacturing industry: black, white, and yellow. Furthermore, the PCB software applies standard fonts in silkscreen layers, but you can still select more fonts from the system. This article contains everything you need to know about PCB silkscreen.
What is a PCB Silkscreen?
Think of Google map roads and streets that lack texts and landmarks to provide more direction. Do they make any sense? No, of course! Now, a PCB silkscreen plays the same role as the landmarks and text. It offers text-based information about various circuit points, parts, and extra circuitry as per the requirement.
With the modern advancement in technology, a PCB silkscreen provides beautification images in a silkscreen artwork design. In this regard, you should avoid overlooking the design’s primary role and making the information hardly unreadable.
Now that you understand what a PCB silkscreen is. Let us have a closer look at the importance of a silkscreen.
The Role of a PCB Silkscreen
To lay a proper background on a PCB silkscreen role, let us remind ourselves of the use of a PCB. A Printed Circuit Board (PCB) is also known as a Print Wiring Board (PWB) or Engraved Wiring Board (EWB). It is used to offer mechanical support and connect electronic components. A PCB contains conductive pathways, signal traces, or traces etched from copper sheets laminated onto a non-conductive substrate.
These PCB components and conductive tracks are found all over the board without proper identification. This creates the need to have customized information to assist the manufacturer and end-users in identifying the components like:
- Print company logos, for example, the name of the manufacturer.
- Warning signs, such as High Voltage.
- Version numbers, such as V2, V3, V4, and others.
- Manufacturer identifiers.
- Testing points.
- Component numbers and orientation.
- Processing types.
Generally, these are the roles of a PCB silkscreen:
- It helps to quickly identify circuit points, like testing points, part interconnect, etc.
- You can use it to troubleshoot circuits if you get an undesired outcome or a defective component.
- It will help you to identify components when replacing or designing evaluation requirements quickly.
- It acts as a safety precaution by showing warning signs, like high voltage, grounding, and others.
- As a manufacturer, you can also use silkscreen for branding and marketing purposes. Moreover, it also protects against illegal duplication of the circuit design.
You can also use silkscreen for product evaluation purposes, like rating verifications. It is important to note that your silkscreen information will depend on your board size. If you have a small board, ensure you prioritize the critical information.
The PCB silkscreen process affects the overall PCB quality. You will learn more about this in the next chapter of the PCB screen printing process.
PCB Screen Printing Process
PCB screen printing is a sub-process of solder masking and others, like baking, UV exposure, and development. Most people consider it the most refined among the four categories because of its general effect on the product’s grading and reliability.
The entire PCB silk printing process comprises 32 steps that can further be grouped into six broad processes. These processes may differ in real scenarios based on the PCB material, quality requirements, and expenses.
Let us dive deeper into each of these 6 processes.
1. PCB Silkscreen Design
In this process, the artwork you designed to be printed on your board is prepared. You can use computer-aided software EAGLE to carry it out easily and creatively.
As part of the PCB design package, the silkscreen section allows you to design the silkscreen layer, circuitry, and other design elements pleasantly. The yellow rectangular shape is the silkscreen outline. You can find it on top of the grey package measurement lines.
Once you have chosen your silkscreen menu, you can proceed with the design easily. You can turn the component placement points into texts via various menu options available. To learn more about the PCB silkscreen design, kindly refer to this Eagle silkscreen tutorial.
2. Board Preparation
Once you have finalized your CAD blueprint, you can proceed to the hardware implementation. Here, you need to carry out some steps diligently to get a high-quality PCB.
First, select the board type you will use in the production process. After that, clean, tape troll, and handle your board well to prepare it for printing. Print the design you prepared in step one on transparent paper. After that, place them on dry silk fabric the way you would want them to look on the actual PCB.
Ensure you maintain the PCB design paper at its original position. To achieve this, mount the designs firmly on the surface with clear tape. Afterward, turn the whole setup (silkscreen and the mounted designs) to face downwards. Cover the upper part with opaque cardboard.
Expose the lower part to UV light for approximately 15 minutes to develop the board silkscreen artwork fully. Then use pressurized water to wash away the emulsion sections that were not cured and expose the designed silkscreen template.
3. Silkscreen Printing
This is where the actual silkscreen printing takes place. For this to happen, you have to fix your board on a printing machine. Consequently, the machine moves the screen upwards, downwards, and sideways for directional printing. The design you created on Eagle is now etched on the board.
Now, to print the silkscreen on the board, place the etched PCB under the silkscreen fabric. Ensure it aligns well with the silkscreen artwork on top. Additionally, fix the PCB properly to ensure it does not move during the application process. This can be achieved using stoppers at the PCB edges.
Next, apply the silkscreen UV curable ink evenly on top of the artwork using a squeegee. From there, dry the PCB for approximately ten minutes with a drying oven. The texts or marking are clearly displayed on the board surface now.
4. Handling Procedures
At this point, you have finished screen printing your board. However, it would be best if you practiced proper handling to maintain the PCB quality. This is why the biggest steps are done in handling procedures. You should conduct about 12 steps to ensure that your PCB quality is not affected by the silkscreen printing process negatively.
5. Inspection Procedure
You should carry out an inspection process during the handling steps and after the processing steps. The aim is to determine the quality of the board panels you created visually. Besides, this process ensures that the printed information is readable by the human eye. In small boards, ensure you print all the essential information first.
6. Silkscreen Treatment
This is the last step of the PCB screen printing process. Here, you treat your silkscreen print and inspect whether it is ready for use. This will be determined by the quality of the silkscreen process.
Mix an emulsion with a developer in a ratio of about 10:1; if possible, mix them in a dark room. Apply the mixture on the silk fabric surface using a wide squeegee. It is recommendable to apply two layers on every side to create four layers in total. The layers must be even and devoid of spaces or bubbles. It would be best if you allow them to dry naturally, or you can speed up the process with a drier.
PCB Silkscreen Methods
The silkscreen method you will use depends on several factors like time, cost, the required precision, board spacing, the material of board used, etc. We will not dig deeper into each of these aspects in this article. For now, let us go straight into the PCB screen printing methods.
1. Manual Screen Printing
This is the oldest and most affordable PCB silkscreen printing method. You use epoxy ink to conduct the process. Generally, you push the ink into the laminate and dry to achieve the impression on your PCB.
The major benefit of the manual screen printing process is that the setup requirements are more manageable. This makes it a preferred option for most tasks. On the other hand, this method demands a large board size and impression drying. This is because of the bigger text size dominant in this method.
It is advisable to use the manual screen printing method when you want to minimize expenses, and board spacing is not a problem.
2. Liquid Photo Imaging (LPI)
In liquid photo imaging, you coat the laminate through the epoxy first. The epoxy is a liquid and has photo imaging properties. Afterward, you should transfer the silkscreen sketch to plates via exposure to UV light.
Liquid photo imaging results are better in precision than those from the manual silkscreen method. Besides, this method requires less space than manual screen printing. Nevertheless, this method consumes more ink and setup time than any other screen printing method.
It is advisable to opt for the liquid photo imaging method when you want to save PCB space and fineness.
3. Direct Legend Printing (DLT)
The direct legend printing method uses the same principle as a paper printer. It would help if you had high-end inkjet printers with the ability to transfer ink into boards. The good thing with this method is that your CAD application information is directly printed onto the board. Innovators have also upgraded the direct legend printing ink to acrylic, condensing drying time.
Direct legend printing is a modern screen printing method with high accuracy and time efficiency features. The plan also has a low text height capacity equal to or higher than 0.02 inches. You should not apply heights that are less than 0.02 since they may be unreadable by the human eye.
The disadvantage of the direct legend printing method is that you cannot use it for PCBs with silver materials. Additionally, there is a restriction for acrylic ink in some use cases.
Generally, selecting the appropriate PCB screen printing method will help you save on the overall cost and time.
|Font size||0.889 mm (0.035 in)||0.762 mm (0.03 in)||0.508 mm (0.02 in)|
|Clearance||0.127 mm (0.005 in)||0.1016 mm (0.004 in)||0.0762 mm (0.003 in)|
|Accuracy and legibility||Good for large font sizes.||Better||Best|
|Setup and application||Easy and quick||Slowest||Fastest|
|Materials||Epoxy ink||Photo-imaginable film (produces more waste than manual or DLP.)||Acrylic ink (can’t be applied on silver surfaces or for applications like aerospace.|
The table above has compared the three PCB screen printing methods. As illustrated, they each have their pros and cons. Understanding these attributes will help you to design a quality and low-cost silkscreen.
Understanding the Cost of a PCB Silkscreen
The PCB silkscreen cost is classified under the non-recurring tolling head in the production process because of the fixed cost aspect. The screen printing process accounts for about 12-15% of the entire PCB production expenses.
Text design denotes character width, height, spacing, thickness, spacing, and placement variation. The artwork expenses are usually not separately calculated. The cost of ink depends on the screen printing method you use. Acrylic ink is commonly used with the direct legend printing method, while the other methods use epoxy ink.
The cost of ink is determined by other properties such as substrate compatibility, adhesion properties, curing procedure, and immunity to acidic or alkaline treatment. Besides, the ink color is another determinant. For example, white-colored inks are cheaper than any other color. It is estimated that about 5% of the overall printed circuit board expenses can be minimized with cost optimization for board silkscreen regarding material preference.
The PCB screen printing method also affects the overall cost. For instance, liquid photo imaging and direct legend printing cost more than manual screen printing due to the extra setup expenses. Another important aspect to consider in silkscreen cost is whether you plan to print the artwork on either side or one side. Printing on both sides will cost you almost twice as on a single side.
DIY PCB Silkscreen
There are a few points to consider for a successful DIY PCB silkscreen. First, you must understand the application of the PCB CAD tool to design the color, font, and text placement. This is what is referred to as artwork – a crucial part of the silkscreen process. You must apply a creative approach to make your board appealing and readable at the same time.
The second learning factor is the ink laminate transfer. This is an elusive process with a direct impact on the end product. To transfer the ink laminate, stretch your polyester screens on an aluminum sheet, and coat them. If you fail to position your screens and panels in a synchronized way, you will end up damaging the entire PCB. Once you finish the coating process, dry it adequately before use.
Still, some aspects can make you seek the services of a PCB manufacturer. If you want your PCB screen printing process to be done professionally, kindly contact your preferred PCB service provider.
Design Guidelines for PCB Silkscreen Design
Silkscreen designs vary from very simple to complex designs. Failure to include adequate and necessary information in your PCB silkscreen design is like having limited knowledge and landmarks on a Google map. The travelers – in this case, PCB manufacturers and end-users- will easily get lost.
The guidelines below will assist you in making maximum use of your silkscreen.
Find out about the method your PCB manufacturer uses to make silkscreens.
Most manufacturers cannot make silkscreens using all three-screen printing methods. Thus, contact your preferred manufacturer to find out about their silkscreen manufacturing capacity. The PCB screen printing method you use affects your primary design elements such as size clearance, location of silkscreen markings, component pads, traces, and vias.
Account for silkscreen items during PCB layout.
For your silkscreen to be readable, markings such as polarity, pin one, and reference indicators should be adjacent to their related components. As you are making your design, you should consider these additional spacing requirements to avoid overlapping or covering the indicators.
Choose your fonts based on your manufacturer’s printing method.
Some printed circuit board design packages will allow you to make almost any silkscreen font style. Nevertheless, your manufacturer may only be able to support a few fonts. Therefore, contact your chosen PCB service provider to ensure you include fonts that they support.
Do not overuse silkscreen markings.
You can be tempted to include signs for every component and other informational imagery that may be useful in assembly, testing, repair, and use of the end product. But with the current demand for miniaturized and compact boards, it is almost impossible to include every bit of information.
In this regard, prioritize your markings as described below:
- Start with regulatory requirements like lead-free labeling needed by J-STD-609A Marking and Labeling of Components, PCBs, and PCBAs to identify Lead (Pb), Lead-Free (Pb-Free), and other IPC aspects.
- Secondly, consider manufacturer identification and markings like PCB component number, serial number, labels, and company logo.
- Thirdly, prioritize assembly aids such as polarity and pin one indicators. Include reference indicators according to the available board space.
- Fourthly, consider tasting aids like point and jumper indicators.
According to the above guide, if you prioritize your marking, you will undoubtedly make maximum use of PCB identification and labeling, even if you have a small board.
How to Choose a PCB Silkscreen Manufacturer
It is wise to seek services from a reliable PCB silkscreen manufacturer if you want high-quality products and quick-turn services. PCB service providers have developed robust learning curves that best suit the PCB screen printing process. However, you should still consider some points when seeking the services of a PCB manufacturer.
First, consider the artwork aspect. Ensure you can maintain a close relationship with your manufacturer to finalize your CAD or manual board design before embarking on the actual production. This is the stage where you can determine your font size, clearance spacing, color, single or double-side printing, and other essential silkscreen design considerations. Keep in mind that these aspects directly influence the overall cost. Therefore, select them diligently with the help of your service provider.
Once you are done, double-check your design for errors and readability issues. You can use the die design severally, but redesigning it because of an accuracy problem will consume your time and money. The best thing to do is to collaborate with your manufacturer to make sound decisions.
You can analyze the manufacturer’s capacities by inquiring about your requirements from him. A good service provider will display a strong command over the subject and be willing to guide you through the process. As a matter of fact, choosing a reliable and experienced PCB manufacturer like MKTPCB will make your work hassle-free.
MKTPCB is the leading turnkey PCB manufacturer and assembling service provider in China. We offer low-cost, quick turnaround and quality PCB products and services that will satisfy your requirements. Our PCB services also include silkscreen capacities that meet a wide range of design requirements. Furthermore, to assist you in getting started on the right path, we provide you with DM check data.
PCB silkscreen is a delicate process that can affect the overall quality of your PCB and add value through refined artwork. The cost factor is a crucial aspect to consider in your design process. In addition, a comprehensive understanding of the entire screen printing process and the advantages and disadvantages of each printing method makes it easier to decide whether to DIY or seek the services of a PCB manufacturer.
If you are ready to have your silkscreen design manufactured by an experienced and reliable PCB service provider, use our quote tool to upload your CAD and BOM files. You can still contact us via email if you want more information regarding our PCB silkscreen services.