Why You Should Care About the Silkscreen: PCB Identification and Labels

Tempo Automation

June 12, 2018 , in Blog

One of my pet peeves about driving is when other drivers forget to use signal lights. It’s as if they are oblivious to the fact that there are other cars on the road. As with a lot of safety measures, implementing them may be annoying or easy to forget. However, it is important to remember that using signal lights isn’t for your benefit; it’s to indicate to other drivers that you plan to turn or change lanes so they can be alert. The same is true for the silkscreen PCB layer of your design. The silkscreen is there for others, primarily your PCB assembly provider but also for anyone testing or troubleshooting the board.

The silkscreen layer contains invaluable information for PCB assembly. This layer contains information about the location of components and their polarity; these details are critical for the proper placement and orientation of components. The silkscreen layer also contains important identification information like identifiers, component labels and logos. For your silkscreen to be effective and useful, it must be clearly legible with readable fonts. The best way to ensure legibility and clarity is to ask your contract manufacturer (CM) to assist you in employing good silkscreen PCB design guidelines as part of your DFM. The importance of the silkscreen PCB layer to your board design can be best understood by examining its impact on assembly and testing.

Importance of the Silkscreen PCB Layer to Assembly

In years past, the primary method of silkscreen creation involved using a stencil to directly apply ink to the board surface. Today, the most common silkscreen PCB printing techniques are Liquid Photo Imaging (LPI) and Direct Legend Printing (DLP).

🖋 LPI is the most time-intensive approach, but yields the best resolution of images and text. The process is similar to the method used to apply solder mask and involves exposing an imageable film to ultraviolet (UV) light.

🖋 DLP is faster than LPI. For this method, an inkjet printer is used to print the silkscreen on the board with acrylic ink.

Although silkscreen PCB application is performed during board fabrication, it is used for the manufacturing steps of the PCB assembly process. Principally, the steps that involve placing or mounting components. The silkscreen markings used to accurately place components include the following:

  • Reference indicators – these identify the component type from the BOM.
  • Pin 1 indicator – this indicates which pins connect to what pads of the footprint.
  • Polarity indicators – these provide the orientation of polarized components.
  • Component outline – this, in conjunction with the landing pattern, indicates where the component should be placed.

For components with small numbers of pads or simple shapes, the absence of the component outline may be acceptable for general placement. However, there still exists the possibility of asymmetrical placement, which may lead to problems during soldering, such as tombstoning. The absence of reference, pin 1 and polarity indicators may lead to incorrect component orientation or placement, which could negatively affect device functionality. Silkscreen PCB layout accuracy is very important for board assembly as well as testing.

Importance of the Silkscreen PCB to Testing

Another important usage of the silkscreen PCB layout is informing the engineer or technician of the location where measurements should be taken during testing or troubleshooting. Along with component manufacturer guidelines, these can be used to verify device performance or help identify potential failure causes. Silkscreen PCB markings used for testing and troubleshooting may include:

  • Test points – these are dedicated locations on the board where the desired values are usually known, which makes them useful as first indicators of problems with board operation.
  • Warning symbols – these may be used to indicate unusually high voltages or other parameters that should be avoided or require special care.
  • Part numbers – these are extremely helpful if device information, like datasheets, is not readily available.

Tips for Silkscreen PCB Design

As discussed earlier, using a silkscreen PCB layout is an important aspect of board design and not including it can cause serious problems for PCB assembly and testing. The silkscreen is also used for labeling, which may include manufacturer information, testing certifications, model or serial numbers. In order to be effective and useful, the silkscreen must have clearly readable text, provide sufficient image resolution and, most importantly, be accurate. Here are a few tips to help you ensure that your silkscreen PCB layout can be used for its important roles in PCB assembly, testing and identification:

  • Tip 1: Only use fonts approved by your CM as some fonts, although easily created in software, are difficult to generate during board manufacture.
  • Tip 2: Use white or black instead of other colors to provide the best contrast with your board’s solder mask color.
  • Tip 3: Make sure to follow your CM’s clearance and dimension guidelines. This will ensure that your silkscreen items do not get covered by components and are easily visible.
Tempo‘s Custom PCB Manufacturing Service

  • Performs entire turnkey process in as fast as 3 days.
  • Emphasizes DFM to eliminate time-consuming back-and-forth design corrections.
  • Performs BOM verifications to reduce possibility of component obsolescence issues.
  • Sources components from the most reputable suppliers in the industry to reduce procurement time.
  • Performs multiple automated inspections during assembly to ensure PCB quality for prototyping.
  • Provides support throughout the PCB manufacturing process, beginning with design.
  • Smooth transition from prototyping to production.

Remember, adding and creating silkscreen PCB layout indicators, labels, markings, text and logos helps you assist others, including your CM with PCB assembly as well as engineers, technicians and end users with testing and troubleshooting. However, to be clear and readable, your silkscreen must meet your CM’s printing capabilities and font requirements. To avoid any issues with your PCB assembly, it is best to incorporate these requirements from day one of your PCB design.

And to help you get started on the best path, Tempo furnishes information for your DFM and enables you to easily view and download DRC files. If you’re an Altium user, you can simply add these files to your PCB design software.

If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on CAD files or how to incorporate your design into a CAD format, contact us.

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