Do you have to incur additional costs for silkscreen when designing or ordering your PCBs? If so, it’s essential to understand what silkscreen is.
The silkscreen layer is created by the designer as a separate layer and integrated with the other coats of a printed circuit board. Whether or not the fabricator applies the silkscreen (screen print) to the printed circuit board depends on whether the designer has included this request in the particular instructions. On the silkscreen layer, the designer may include various pieces of information.
- All elements on the circuit board are assigned reference designators.
- components Orientation
- components Polarity
- components Outline
- Test Points
- PCB version number
- Printed circuit board serial number
- Testing certifications
- Manufacturer’s logo
- Warm symbols
If a PCB contains only SMCs/surface mount elements, the designer can utilize a single silkscreen layer for the upper layer of the circuit board. However, if the printed circuit board has THCs or through-hole components, the designer can divide the silkscreen into two parts. The top layer of the board has essential information on it, while the bottom layer has labels that show where things should go and which way they should face. When the circuit board is made, a special kind of ink is used that won’t mess up the parts that need to be soldered. The person designing the hdi circuit board must carefully choose the correct ink for the labels, so it doesn’t mess up the soldering parts.
Methods Of Applying Silkscreen PCB
To manually transfer the information onto the PCB, the fabricator employs the silkscreen details to create a transfer screen. Alternatively, they may adopt modern techniques to print the information directly onto the printed circuit board, eliminating the need for a transfer screen.
· Manual Printing
Manually printing a design onto a circuit board using a particular screen can be helpful if the lines are at least 0.007 inches thick and the design is accurate within 0.005 inches. The fabricator uses a unique nylon fabric to make a stencil that matches the design. They stretch this stencil onto a frame and use ink to print the design onto the circuit board. Finally, they bake the board in an oven to make sure the ink stays on the board.
· Liquid Photo Imaging
When line widths are thinner, like four mils, hand-set printing becomes unsuitable, and fabricators turn to the LPI method. To implement this method, they begin by coating the printed circuit board with a light-sensitive epoxy layer. They then transfer the screen print image onto the epoxy & reveal it to ultraviolet light. After exposure, they remove the undeveloped portion of the epoxy, departing the silkscreen image on the printed circuit board. The board then undergoes curing to fix the image in place.
The LPI method, while providing greater precision than the Letterpress printing technique, demands more ink consumption and longer setup time.
· Direct Legend Printing
Out of all available methods, this one stands as the most precise yet costly. It involves a computer, Computer-Aided Design software, an inkjet projector, & acrylic ink. The computer commands the visualizer to deposit ink onto the printed circuit board, following the silkscreen design, and then undergo ultraviolet curing.
Why Use Silkscreen PCB?
Using silkscreen printing on the printed circuit board offers numerous advantages. One example is with the silkscreen print:
- The reference designators can aid assemblers in precisely placing components on PCB.
- Assemblers can quickly determine the polarity and orientation of components through the silkscreen print.
- During troubleshooting or measurements, PCB technicians can identify the testing nodes on the board.
- By recognizing warning signs for high potential, technicians can set appropriate voltage & current levels.
- When repairing the PCB, technicians can readily identify which components must be replaced.
How To Design A Silkscreen PCB?
For better PCB part designation, assembly & testing, it is essential to ensure that the Silk print meets specific design specifications, as recommended by Rush printed circuit board USA. These specifications include:
- Fonts — When it comes to silkscreen print on a printed circuit board, not all fonts are appropriate. To ensure that the printed text is legible & readable, the designer should seek guidance from their contract producer regarding which fonts are suitable for the process.
- Color — When the fabricator places the silkscreen onto the solder mask coat, the ink color for the silkscreen must provide a noticeable difference from the color of this solder mask. While white is the most suitable color for a green PCB mask layer, any color that creates a clear contrast and makes it easy to read the text or design is also acceptable.
- Clearance and Dimension — To ensure legibility & readability, it is crucial to maintain proper clearance & dimensions for the lines & letters on the silkscreen. The designer should seek guidance from their contract producer to meet these requirements. The ink from the silkscreen printing mustn’t infringe upon the solder pads under any circumstances.
- PCB Design Guidelines and DFM — Including the details in the printed circuit board design guideline and DFM is necessary to establish a uniform design for silkscreens across various PCBs.
Conclusion
Rush printed circuit board USA suggests that incorporating silk screen printing on a printed circuit board can significantly enhance its quality & reliability. The addition of silkscreen aid in both the assembly & testing processes while also considerably reducing the time required for troubleshooting. Despite the added expense of Incorporating a silkscreen print layer, the improved printed circuit board quality & reliability makes it a valuable investment.
