How Machines Revolutionize PCB Silk Screen Printing

The layer of printed text, symbols, marks, and images on a printed circuit board's (PCB) surface is referred to as PCB silkscreen. As part of the PCB manufacturing process, it printed specific ink or substance that resembles ink onto the PCB surface so that it offers information on component placement, assembly instructions, and identification. When it comes to producing high-quality printed circuit boards (PCBs), precision and accuracy are paramount. Advanced PCB silkscreen printing machines that deliver exceptional results. PCB screen printers are designed to meet the demanding requirements of modern electronics manufacturing, providing precise and reliable printing solutions.

Printing machines utilize state-of-the-art technology to ensure optimal printing performance. Equipped with advanced features such as automatic stencil alignment, adjustable squeegee pressure, and precise control systems, our machines deliver consistent and accurate printing results, even for complex PCB designs. PCB screen printing machine, designed for enhanced efficiency and productivity. This automated solution eliminates manual intervention, enabling continuous and uninterrupted printing operations. Which streamlines the production process, reducing labor costs and increasing throughput.

In the following chapters, we will explain in more detail the advantages of silkscreen in PCB. At the same time, we will also explain the three methods of creating silkscreen and their corresponding advantages and disadvantages. And how the machines revolutionize PCB silk screen printing.

What is PCB Silk Screen Printing?

Think of roads and streets that lack direction/distance texts and landmarks. Do they make any sense? Similarly 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. Silkscreen is mainly used in marking test points and annotating component prefix names. Silkscreen can be placed during fabrication using a UV liquid photo-imaging process, which is similar to that used for solder mask application. If you need very small linewidths, your fabricator may use an alternative process called “direct legend printing”. The proper process is given in detail at the end of this article. Traditionally, silk screen printing was performed manually, requiring significant skill and time. However, as PCBs have become more complex and production volumes have increased, automated machines have become indispensable.

What Should Go on PCB Silkscreen?

In particular, we can include a variety of information in the silk screen layer, including warning signs, assembly instructions, business or brand logos, component names, indications. Here is the proper list:

● Print company logos, the name of the designer/ manufacturer

● Warning signs, such as High Voltage

● Version numbers, such as Ver1.0, V2.0, V3.0, V4.0, and others

● Testing points

● Component numbers and orientation

● Connector pinouts, especially for pin headers

All of this information can get very cramped on a dense board; we’ll look at some ways you can organize your silkscreen markings later in this article. The example above shows an example PCB assembly board containing some of the information in the above list.

Limitations of Manual Silk Screen Printing

1. Time-Consuming

Manual printing processes are labor-intensive and slow, limiting their suitability for high-volume manufacturing.

2. Inconsistency

Achieving consistent quality across multiple boards is challenging, especially for intricate designs or fine details.

3. Errors and Waste

Human error can lead to misalignment, smudging, and defective prints, resulting in material waste and increased costs.

4. Limited Scalability

Manual methods struggle to meet the demands of modern electronics manufacturing, where speed and precision are critical.

How Machines Revolutionize PCB Silk Screen Printing

1. Enhanced Precision

Modern machines leverage advanced technologies such as:

● Automated Alignment: Ensures perfect positioning of the silk screen layer, minimizing errors.

● High-Resolution Printing: Achieves intricate details and fine text, even on densely packed PCBs.

With machines, manufacturers can maintain uniformity across large production batches, reducing defects and ensuring higher quality.

2. Increased Speed

Automated silk screen printing machines operate at significantly higher speeds compared to manual processes. They can:

● Handle multiple boards simultaneously.

● Reduce setup and transition times between different designs.

This speed boost is vital for high-volume manufacturing environments where time-to-market is critical.

3. Improved Durability of Prints

Machines use optimized techniques and controlled environments to ensure:

● Proper ink adhesion.

● Uniform layer thickness.

● Long-lasting prints resistant to wear and environmental factors.

4. Versatility in Design

Advanced machines support a wide range of printing options, including:

● Multiple colors for enhanced clarity and branding.

● Custom logos and detailed graphics.

● Adaptability to different PCB sizes and shapes.

5. Reduced Material Waste

Automated systems minimize waste by precisely controlling ink usage and reducing the likelihood of errors. This not only saves costs but also aligns with sustainable manufacturing practices.

6. Integration with Other Processes

Modern PCB silk screen printing machines can seamlessly integrate into automated production lines, synchronizing with:

● Solder mask application.

● Component placement.

● Quality control systems.

This integration further streamlines manufacturing and enhances overall efficiency.

Key Features of PCB Silk Screen Printing Machines

1. High-Resolution Printers Capable of printing at resolutions up to 50 microns, ensuring crisp and clear markings.

2. Advanced Vision Systems Incorporated cameras and sensors for real-time alignment and quality assurance.

3. User-Friendly Interfaces Intuitive software allows easy design input and customization.

4. Scalability Machines can handle small prototype runs as well as large-scale production batches with minimal adjustments.

5. Eco-Friendly Operation Many machines incorporate low-energy technologies and support eco-friendly inks, reducing their environmental footprint.

Challenges in Adopting Machine-Based Printing

1. Initial Investment

Purchasing and setting up automated silk screen printing machines require significant upfront costs. However, the long-term benefits often justify the investment.

2. Maintenance Requirements

Regular maintenance is essential to keep machines running efficiently and prevent downtime.

3. Training for Operators

Skilled operators are needed to manage and troubleshoot these machines, necessitating training and upskilling efforts.

Best Practices for Machine-Based Silk Screen Printing

1. Choose the Right Machine Select a machine that matches your production needs, considering factors like resolution, speed, and compatibility with PCB designs.

2. Optimize Designs for Automation Ensure PCB designs are well-suited for automated printing by:

● Including adequate clearances.

● Avoiding overly intricate patterns that may complicate the process.

3. Regular Maintenance Schedule routine maintenance to keep machines in optimal condition and reduce unexpected downtimes.

4. Leverage Software Capabilities Utilize design and simulation tools to test print layouts before production, reducing trial-and-error efforts.

Future Trends in PCB Silk Screen Printing

1. Digital Printing Technologies Digital printing is emerging as an alternative to traditional silk screen methods, offering even greater precision and flexibility.

2. Artificial Intelligence Integration AI-driven systems can analyze print quality in real time, enabling immediate adjustments and further reducing defects.

3. Sustainability Innovations Future machines are likely to incorporate even more eco-friendly practices, such as water-based inks and energy-efficient operations.

Features of Auto-Printer

High speed: the automatic screen printer has its own unique frequency conversion speed regulation device, the printing speed can be adjusted from 20 to 70 times per minute auto screen printing machine.

Cost-effective: the auto printer has its own electronic counter, which can automatically shut down according to the pre-designed total number, saving a lot of manpower and ink material.

Good quality: the automatic screen printer is very accurate in point and color, because it is equipped with a multi-color printing electric eye device, which can improve the quality of printing.

Good adhesive: the adhesion of the screen machine is very good, and the ink layer is relatively thick, so the text legend is not easy to fade.

Multi-aspect: the fully automatic screen printer can not only be used alone, but also can be connected to a UV dryer, or a slitting machine, a reminder, and other auxiliary machines.

With the help of Automatic silkscreen printers, we are able to provide “faster” and more “efficient” service to our customers, warmly welcome to contact us, we are ONLINE always!

Manufacturing processes of printing silkscreen

Screen fix

Step 1, we need to fix the screen on the base or workbench with a fixture, and leave 3-5mm distance away from the positioning plate when we put the screen.

Align and position

Step 2, we need to place the circuit board on the positioning plate with right-angle positioning method or stud registration method (generally use 2 positioning pieces), make it fixed and aligned, then put down the stencil frame and adjust the positioning button, so that the PCB outline is roughly overlapping with screen. Next step, perform initial align boards according to the positioning holes or outline line, then gradually adjust to the optimal position based on pads.

Silkscreen ink selection and fine-tune

Step 3, we need to select the silkscreen ink according to the customer requirements, put down the screen frame and poured ink into the screen frame, and then select the length of the appropriate scraper for the trial printing sample, and fine-tune the positioning until accurate.

Trial printing

Step 4, we will need to do trial printing the prototypes with transparent character alignment film and check to see if there is a legend deviation, if no, then we can proceed with mass production, but if not, then the positioning should be fine-tuned again, rip off the defective film and affixed with the new one then printing again, repeat trail until qualified.

Screen Printing (Manually):

Step 5, let’s place the circuit board (which have finished surface treatment process) on a fixed position, put down the screen frame, and then hold the scraper with both hands, at an Angle of 50°- 60 ° with even force on the scraping screen surface from front to back or from back to front. The printing material is subjected to the pressure of the scraper through the printing mesh hole and printed on the circuit board. After the scraper passes through, the screen recovers by its own tension. After the scraper is finished, the screen frame is lifted, and the sealing screen printing material is scraped back.

Screen Printing (Auto Printer):

Step 6, the Angle of the scraper is an external “eight” font, usually between 20-30 degrees, you can choose the printing times according to the actual needs.

In the past, most of the factories make the screen printing manually, it is time consuming and limited to relatively short lengths of 60 yards. So, in our manufacturing line, we have imported the automatic flat-bed screen printing.

PCB Screen Printing Process:

The PCB screen printing process involves applying non-conductive ink, typically white, black, or yellow, to label components, test points, and other important markings. Here are all the steps from design to final product:

1. Design Preparation: The silkscreen layer is created in PCB design software and turned into a Gerber file. This Gerber file includes all the information regarding PCB.

2. Screen Preparation: 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.

3. Printing: Then place the fabric on board and mount the design firmly on the surface with clear tape. Ink is applied through the screen onto the PCB using a squeegee.

4. Curing: Expose the board design to a UV machine covering the other side with opaque material. The ink is cured via UV light or heat to solidify the markings.

5. Quality Check: The board is inspected to ensure clear, accurate labels.

This process ensures quick identification of components and aids assembly and troubleshooting. To know more about the PCB design see our ultimate guide on PCB manufacturing process.

Types of PCB Silkscreen:

In PCB manufacturing, there are primarily two types of silkscreen processes utilized:

Manual Screen Printing

Liquid Photo Imaging (LPI)

Direct Legend Printing (DLP)

Each of these methods has its unique characteristics, advantages, and disadvantages, and their application largely depends on the specific requirements of the PCB design.

1. Manual Screen Printing: Involves using a stencil to manually apply ink. This method is cost-effective for simple designs but less precise for complex PCBs. The process involves:

Coating the screen with a layer of photosensitive emulsion

Exposing it to light through a film positive of the design

Washing away the emulsion to create a stencil of the design on the screen.

Applying the ink to the screen, through the stencil onto the surface to be printed.

2. Liquid Photo Imaging (LPI): A photosensitive liquid epoxy is applied onto the PCB, which is then exposed to ultraviolet light through a film that carries the desired legend pattern. Which creates the fine and detailed markings on the PCB. It’s ideal for high-density boards. However, the process is more time-consuming and costly compared to other methods. The need for UV exposure and development adds to the manufacturing time, and the use of photosensitive epoxy and films increases the material costs.

3. Direct Legend Printing (DLP): Uses inkjet printing technology to apply the ink directly onto the PCB. DLP is fast, accurate, and eliminates the need for stencils, making it a preferred option for modern PCB production. Since it does not require any films or UV exposure, the DLP process can significantly reduce the manufacturing time. Although it may not match the high resolution offered by the LPI process. Therefore, DLP may not be suitable for PCBs that require high durability of the silkscreen.

Each method has its advantages in terms of cost, accuracy, and complexity.

Manual screen printing

On a silkscreen PCB, manual screen printing employs a screen printing technology to apply ink to a PCB while doing it by hand. To be specific, when the line width is over 7 mm and the line's registration tolerance is 5 mm, this procedure can be applied. You will need a nylon tracing stencil and PCB silkscreen minimum text size for this procedure. Using the stencil, we imprint the oil onto the plate. The PCB board will then need to be cooked in a curing oven and allowed to solidify.

Pros: Firstly, it is really cost-effectiveness for small-scale production. As for small-scale production, equipment, and setup costs are typically lower compared to using automated printing methods. Secondly, this method is versatile. Fabrics, paper, plastics, and PCB are just a few of the materials hands may print on. It is appropriate for a variety of applications since it can print on both curved and flat surfaces. Moreover, design modification options are flexible with manual screen printing. Small runs or one-off printing benefit from its ability to be changed and adjusted on the fly.

Cons: However, Manual screen printing on screen-printed circuit boards requires skilled operators who can accurately align the screen, apply consistent pressure, and ensure proper ink coverage. Therefore, it is a labor-intensive process. So for larger production volumes, automatic screen printing machines are often used to increase efficiency and accuracy. Also, more sophisticated printing techniques like LPI or DLP may reach higher levels of resolution and fine detail than manual screen printing. It works best on designs with more substantial components and simpler details.

A person with white gloves operates a printing device, applying pressure to transfer green substance onto a circuit design on a PCB. The scene takes place on a workshop table, resembling a manufacturing setup for electronic components.

Liquid photo imaging (LPI)

We shall initially cover the laminate through the epoxy in liquid photo imaging. The liquid epoxy can image photos. Then, apply UV light exposure to transfer the silkscreen drawing to plates. They commonly used LPI for various purposes, including solder mask application and silkscreen printing.

Pros: Similar to the manual screen printing method, LPI offers versatility. LPI is suitable for a variety of applications in PCB manufacturing, including solder mask application and screen printing. It can be used to create protective layers, text, logos, and other markings on PCB surfaces. Also, complex design replication is made accurate and efficient with LPI. Consistency is ensured, and we removed manual corrections or alignment with the use of digital files and UV exposure. It is noticeable that different from the manual screen printing method, LPI allows for the creation of high-resolution patterns and designs on the PCB surface. It can produce fine features, intricate details, and precise registration between different layers of the PCB.

Cons: When compared to automated techniques, LPI might be a time-consuming procedure. Particularly for intricate designs or big PCB quantities, the exposure and development phases could take longer than expected. Moreover, the LPI process is relatively complex, including ink coating, exposure, and development. It requires careful control of variables such as exposure time, developer, and drying conditions. To achieve consistent results, a precise and controlled environment is required.

Direct legend printing (DLP)

DLP is a digital printing method that utilizes a projector or light source to selectively cure a liquid resin layer by layer.

Pros: DLP offers high precision and resolution, allowing for the creation of intricate and detailed patterns on the PCB surface. It can create intricate patterns, intricate geometries, and accurate circuit traces. Also, when comparing DLP with traditional techniques, production time can be reduced. It allows for the simultaneous curing of numerous layers, which speeds up manufacturing cycles and prototyping. Moreover, DLP enables customization and flexibility in design. Digital files allow for quick prototype and design iterations due to their ease of modification and adjustment.

Cons: DLP systems can be expensive to acquire and maintain. Specialized tools, such as curing systems, resin ingredients, and DLP projectors or light sources, can need a large initial outlay of funds. Not only that, the material selection is relatively limited by using DLP. Resin-based materials, which could have distinct material qualities from traditional PCB substrates, are the main materials for which DLP is appropriate. There might be fewer alternatives available in terms of the variety of materials that can be used for DLP.

Conclusion

The transition from manual to machine-based PCB silk screen printing marks a significant milestone in electronics manufacturing. With their precision, speed, and scalability, modern machines address the challenges of traditional methods, enabling manufacturers to meet the demands of complex and high-volume production. By investing in advanced printing technologies, the industry continues to push the boundaries of quality and efficiency, setting new standards for PCB manufacturing.