What is  top-of-board silkscreen on a printed circuit board?

| February 12, 2026 | Amateur Radio (Ham Radio) | No Comments

In the world of PCB design, the top-of-board silkscreen is the layer of ink used to print identifying information directly onto the top surface of the circuit board. It acts as a reference map for anyone assembling, testing, or repairing the device. Think of it as the “labels” on a control panel; without them, you’d have a hard time knowing which part goes where.

What is Included in the Silkscreen?

The silkscreen layer typically consists of several key elements:

  • Reference Designators: Labels like R1, C5, or U2 that link a physical component to its position on the schematic.
  • Component Outlines: Lines showing the physical boundary of a part (like a rectangle for a resistor or a square for an IC).
  • Polarity Markers: Indicators such as a “+” sign for electrolytic capacitors or a small dot/notch for Integrated Circuits (ICs) to ensure they aren’t soldered backward.
  • Logos and Branding: Manufacturer names, version numbers (e.g., “v1.2”), and certification marks like CE or FCC.
  • Pin Numbering: Small numbers next to connectors or headers to identify specific pins.

How is it Applied?

Traditionally, this layer was applied using a literal silk screening process (hence the name). Silk screening (or screen printing) is a versatile, durable, and popular printing technique where ink is pushed through a stenciled mesh screen onto materials like fabric or plastic. Modern manufacturing usually uses one of two methods:

  1. Liquid Photo Imaging (LPI): A light-sensitive epoxy is coated on the board, exposed to UV light through a mask, and developed. It provides high resolution but can be time-consuming.
  2. Direct Legend Printing (DLP): Similar to an inkjet printer, this method sprays the ink directly onto the board. It is the most common modern method because it is fast and handles fine details well.

Design Considerations

If you are designing your own boards, here are a few “pro-tips” for the silkscreen:

  • Avoid Pads: Never place silkscreen ink on top of a solder pad. The ink acts as an insulator and will cause a “cold joint” or prevent the solder from bonding to the copper.
  • Readability: Ensure the font size is large enough to read with the naked eye (usually at least 0.8mm to 1.0mm high).
  • High Contrast: Use a color that stands out. While white is the standard for green boards, you’ll see black ink used on white or yellow boards for better visibility.