Introduction
You already know that all electronic devices consist of a circuit board. PCBs, or printed circuit boards, are an integral part of today’s electronics. Green boards with intricate lines and patterns are called PCBs. In electronic devices, the markings on the PCB ensure that all of its components function together smoothly. Manufacturing a PCB consists of several components and steps. The final stage in making a printed circuit board (PCB) is to add a silkscreen to the uppermost layer.
Silkscreen is the process of applying a coating of ink traces to a circuit board in order to identify its components, warning symbols, test points, marks, logos marks, etc. Typically, the component portion is the side where manufacturers print silkscreen. It occasionally shows up in the solder aisle, but getting it there is costly. A PCB silkscreen aids in the quick recognition of component placements by manufacturers and designers. The PCB silkscreen will guarantee that the parts can be reassembled. The silkscreen will give instructions to the engineer or technician as to where and how components should be placed on the PCB.
This article will provide all the information you need to know about PCB silkscreen, including why it’s so crucial, what the best practices are, and how to properly include it in PCB designs.
What is PCB Silkscreen?
Imagine you’re doing a DIY project to build a futuristic smartwatch from scratch. Your PCB is like the blueprint of this high-tech wearable, and the silkscreen is your way of adding intuitive markers and labels to guide you and anyone involved in the assembly process.
Silkscreen on a PCB is a layer of ink printed onto the board’s surface. It is typically made of a polymer or ceramic material and applied through screen printing. The ink is applied through a mesh screen, which serves as a template for the desired pattern. The screen is placed over the PCB, and ink is forced through the mesh and onto the board. The standard silkscreen colors manufacturers use are black, yellow, and white. You can use common fonts in the design of the silkscreen layer while using PCB software.
It is normally applied on the board’s top and bottom layers. Using a silkscreen, the PCB’s board’s surface may be printed with text, labels, and symbols. Components, their locations, part designations, component numbers, brand logos, and other information are all depicted visually.
Although it has nothing to do with the circuit board’s actual electrical operation, the silkscreen layer is crucial to the process of building, testing, and using the board. Helps find things and put them in the right places so that everything is lined up and in the right orientation. It’s useful for the assembly process since it gives technicians and assemblers easy-to-understand visual clues. Now that you know the fundamentals of printed circuit board silkscreen let’s examine its broader utility.
What Information does a PCB Silkscreen have?
As told earlier a silkscreen on PCB may not have any role in the functioning of a PCB; however, it is valued for the information that it delivers. For instance, it will help anyone to:
Warning Symbols: Recognize caution symbols highlighting high-temperature components requiring user attention and care during handling.
Polarity: Understand part polarity for correct component mounting. Pin markings provide orientation information to ensure accurate assembly.
Test Points: Locate test point indicators on the silkscreen to assist design engineers during PCB testing and debugging.
Reference Designators: Identify components through reference designators, unique identifiers for each assembly location on the PCB.
Numbers: Spot unique numbers on the PCB silkscreen, indicating manufacturer marks, version numbers, and more.
Component Symbols: For specialized parts like diodes and opt couplers, component symbols printed on the silkscreen ensure precise alignment during mounting.
Switch Settings: Default switch settings are instructions on the PCB silkscreen, enhancing board usability.
Dense Components: PINs on silkscreen aid testing and debug support for compact component packages like Ball-grid arrays (BGAs).
Troubleshoot and Repair: Silkscreen marks make it simple to identify and locate individual components, which speeds up the repair process.
Manufacturing Documentation: The Silkscreen markings provide essential manufacturing and assembly documentation. They include copyright notices, company logos, manufacturing dates as well as other vital quality control and traceability details.
Branding: These markings contribute to PCB aesthetics and branding. Incorporating branding elements, logos, and chosen colors enhances the overall visual appeal and professionalism.
What should be the optimum thickness of silkscreen on PCB?
The thickness of the silkscreen on a PCB is influenced by the dimensions of the mesh screen and the quantity of ink used. Generally, the silkscreen in PCB is implemented as a fine coating, typically measuring under 0.1 mm in thickness. This allows for the accurate and precise application of ink without significantly altering the overall thickness of the PCB.
The depth of the silkscreen on a PCB may differ based on various factors, including the method of fabrication, specific demands, and established standards within the industry. Ordinarily, the depth of the silkscreen on the PCB is relatively slender compared to the other layers within the PCB.
In some cases, the thickness of the silkscreen PCB layer usually spans around 0.02 mm to 0.1 mm (20 to 100 microns). Considering that these measurements are rough approximations and can change based on various factors is crucial.
Despite the relatively thin nature of silkscreen in PCBs, it still delivers ample visibility and resilience for the markings. The thickness is under careful supervision to guarantee that it doesn’t disrupt the PCB’s functionality, trigger misalignment of components, or lead to complications during manufacturing.
Guidelines for PCB Silkscreen Design
The first step is to use professional software like AutoCAD or EAGLE to develop the Silkscreen layer. The design incorporates all the relevant text, symbols, and marks for locating and assembling the PCB’s components. You’ll need software skills to develop a silkscreen layout. You should also be familiar with standard layout requirements to achieve a positive outcome.
Color Selection
Careful consideration should be given to the color of the silkscreen. The easy on the eyes, dark colors like black and dark blue aren’t always the best choice. Try to use contrasting colors to make them visible on PCB.
Information
Only the most pertinent details about the circuit and its components should be included when designing the silkscreen. If something is already covered elsewhere on the PCB, there’s no need to repeat it here.
Size of Text
To ensure proper data interpretation, Silkscreen fonts on printed circuit boards (PCBs) must be readable.
The text size and line width will vary depending on the silkscreen technique. The recommended minimum font size for regular silkscreen printing is 50 mil, and the minimum line width is 7 mil. Remember that just because you can reduce the text size doesn’t mean you should. Printing and understanding text becomes more challenging when the font size and line spacing are reduced.
Only two directions should be used to make the silkscreen easier to read. The reference designators should be read from left to right and bottom to top to get a uniform and legible silkscreen.
Do not overlap
The numbers, component names, and other details printed on the PCB silkscreen mustn’t overlap as much as feasible. However, to avoid partial silkscreen removal during the formation of solder mask windows, the silkscreen must not overlap with vias or pads. Silkscreen elements should have at least a 5mil gap between them.
Precise Location
It is preferable to place reference designators near the component they identify. Keeping the reference designators in a single rotation is preferable, although this is only sometimes possible, especially when dealing with tiny, discrete pieces.
To avoid users constantly spinning the board to see the next designator, try limiting the rotation between 0 and 90 degrees.
Avoid silkscreening over vias and holes, and ensure no components obscure reference designators or other important board information. Think about how the final user will interpret your software design if you need help deciphering it yourself.
Avoid high-speed signal wires.
This guideline is for top or bottom-layer micro-strip lines carrying high-speed signals. The phase velocity of a signal traveling along a micro-strip line is material-specific. Silkscreen the line causes the dielectric to be non-uniform, which alters the phase velocity, which in turn causes an impedance discontinuity and poor signal quality.
Now that we’ve covered some of the fundamental rules of PCB silkscreen design let’s take a peek at how this design is dealt with throughout the printing phase of PCB production.
Applying Process of PCB Silkscreen
Silkscreen PCB refers to a printed circuit board that has had silkscreen added to it. It’s a crucial part of the production process as a whole. It fits within the stages of UV exposure, solder masking, baking, and development. Yet, when considering its effect on product grading and overall reliability, you can hype it as one of the most intricate among these processes.
The complete silkscreen process comprises up to a maximum of 32 individual steps. We have grouped these steps into six broader processing areas for you. These processes differ based on the material used for PCB, quality needs, and budget.
Designing the Silkscreen for PCB on Software
This phase involves preparing the design you intend to imprint on the PCB. You can achieve this effortlessly and creatively using AutoCAD or EAGLE software. This software lets you design a dedicated silkscreen section layer alongside other components.
Once you activate the menu for silkscreen, you can continue with your design. The design includes all the markings, symbols, and text required to identify and assemble the components on the PCB.
Using the software, you can follow the above-discussed considerations to design a silkscreen layout on PCB. After the finalization of the design, save it in a format the PCB manufacturer can use.
Preparing the PCB Board for Silkscreen print
Once you have finalized the blueprint, the next step is to transition it to hardware. To ensure high-quality outcomes, follow these steps:
Start by choosing the appropriate board type. We at MorePCB provide comprehensive service and top-tier products. Share your required documents for a quick quote. Why delay?
After selection, the selected material undergoes a cleaning process, then tape application and careful board handling. This readies the PCB for the printing phase. At this point, the PCB layouts should be printed in black on clear paper. Place the designs on the silkscreen panel when it has dried. Line up the silk cloth with the marks on the silkscreen PCB design.
To prevent any movement, secure the designs using transparent tape. Maintain their position and flip the entire setup (design and silkscreen) in a downward direction. Cover the top side with dark cardboard.
Exposing the Ultraviolet light for around 15 minutes finalizes the PCB silkscreen creation.
The emulsion parts not exposed to UV light are removed using pressurized water, revealing the developed template of silkscreen.
Printing Silkscreen on PCB
This phase involves real printing of silkscreen on the PCB. Fix the board onto the printing machine, and the screen moves in multiple directions for accurate printing. The PCB has been etched with the pattern created in the software.
The printed circuit board must be etched before the silkscreen can be transferred onto it. Now you place the fabric silkscreen over the PCB, ensuring that it covers the entire surface. The fabric should be appropriately aligned with the PCB to ensure accurate transfer.
Apply gentle pressure to secure the fabric, ensuring it remains flat and taut. Once the transfer is complete, remove the fabric of the silkscreen from the PCB. Inspect the Ensure that the top silkscreen artwork is aligned precisely.
Use a squeegee to spread white curable UV ink across the silkscreen design. The ink of silkscreen must be cured after it is applied to a PCB substrate to ensure adequate adhesion. In most cases, this is achieved by subjecting the PCB to high temperatures or ultraviolet radiation for 10 minutes in an oven. The PCB surface will be permanently marked by this method.
Ensuring Proper Handling
Even though the printing is done, proper handling remains crucial for sustaining the quality of PCB. For this reason, there are several steps to follow.
Thorough Inspection of PCB Silkscreen
An inspection should take place in the process of handling and processing steps. This ensures that PCB panel quality is visually assessed. This step verifies that the human naked eye can correctly read the information on the board. It is essential to ensure no misprints or omissions.
Treatment of PCB Silkscreen
The silkscreen print is treated and inspected for product readiness in the final stage. After quality assurance, your PCB with completed silkscreen processes is ready. Errors in the silkscreen layer can cause issues with assembly and functionality, so this is a crucial stage of production.
Methods of PCB Silkscreen Printing
There are many considerations when using a silkscreen, such as the time and effort involved in creating it and the cost, precision, and material of the board onto which it will be printed. Therefore, it is up to you to see all of this information. There’s no need to delve further into the specifics now. For the time being, let’s focus on the most common silkscreen methods:
Liquid Photo Imaging
Epoxy lamination of the PCB is a prerequisite for LPI. Since epoxy has photo-imaging capabilities, silkscreen prints can be transferred to the plates by exposing them to UV light.
If you employ the LPI silkscreen technique, you’ll get excellent precision. Compared to silkscreen techniques, this one doesn’t require a large working area. The method’s only drawback is that it requires more time and ink to set up than competing methods.
The LPI technique allows you to reduce the size of your PCB while still getting high-quality silkscreen printing.
Direct legend Silkscreen Printing
DLP is the last option for silkscreen printing on this list. You’ll employ the same basic idea behind page printers. Using a page printer is similar to printing on paper in that the steps are the same. The ink from a high-pressure inkjet printer can be transferred directly into the board, eliminating the need for a further step.
A lot of time and energy can be saved because of the precision of this contemporary silkscreen technique. If you opt for the silkscreen process, you will save both time and money. The only limitation is that silver-based PCBs cannot be used with this technique.
How to determine PCB Silkscreen Cost?
Did you know PCB silkscreen makes up 12–15% of the total PCB cost? Character dimensions such as width, thickness, height, positioning, and spacing are all part of the text layout which contributes to the cost of silkscreen.
The ink cost for your silkscreen in a PCB project depends on the technique you use for printing. Screen printing by hand uses epoxy ink, while digital light processing (DLP) uses acrylic ink. The ink’s color and chemical composition significantly contribute to the final shade.
The price of the ink varies depending on its characteristics, such as its compatibility with substrates, adhesive properties, curing process, and resistance to acid and alkali.
When estimating your silkscreen printing costs, it’s also essential to consider whether you want the artwork printed on both sides—the price increases for both parties.
DIY Silkscreen on PCB
Setting up a PCB silkscreen manual procedure at home or in the office is more intuitive. This operation is a component of MorePCB as a whole. You can rely on us for comprehensive support and premium goods. You can get an instantaneous price quote by sending us the necessary paperwork. So, why are we stalling?
To use PCB silkscreen at home, you’ll need a few things. To create a PCB, you must know how to use design software, choose colors and fonts, and arrange text. This is an essential step in silkscreen artwork. PCB can be more enticing through creative approaches but must still be readable.
Second, the most essential part of the printing process is ink being transferred to the laminate. That’s a delicate operation with severe consequences for the final product. Each step of the manual silkscreen process must be carefully attended to for a high-quality end result.
To begin, an aluminum frame is used to stretch polyester screens. In the second stage, the screens are coated. Incorrect placement of the screen and panels can render the entire circuit board useless.
It’s essential to let the coating dry thoroughly before using it. When designing a PCB silkscreen yourself, make sure to follow all of these processes. But there are still reasons why you’d instead work with a specific manufacturer. Read on for advice on how to pick a manufacturer rather than going the do-it-yourself route.
Choosing a Construction Manufacturer
You must clearly communicate with your contract manufacturer to tailor the PCB silkscreen according to your specifications. Discuss the silkscreen’s dimensions and placement from the start. Ask them how much more it will cost and what method they will use to create and apply the silkscreen. Planning for a successful silkscreen is a crucial element of PCB fabrication.
If you are doing DIY, you should always double-check with your CM to find out what they recommend before beginning work on a PCB silkscreen. For instance, your CM will likely advise you to silkscreen the component according to the manufacturer’s specifications. Your CM probably also told you that you could cut down on manufacturing costs and time by merely printing silkscreen on PCB on only one side of the board.
Conclusion
Silkscreen on PCB is a delicate procedure that can affect your PCB’s overall quality and provide value through refined design. It improves the assembly process by providing essential information about orientation, component placement, and directions. Silkscreen serves functional and quality assurance needs, and its markings can withstand the extreme temperatures and chemicals required in PCB production. When it comes time to finalize designs, you must consider the cost-benefit analysis.
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