What is the Silkscreen in a PCB?

The Silkscreen is the topmost layer of a Printed Circuit Board (PCB) which is used as a reference indicator for placing components on a PCB Board. It requires a specifically formulated ink whose standard color is white, but it can also be Red, Black, Yellow, Blue and a number of other colors.

The silkscreen is used to specify useful information on the PCB board that can help/assist users during assembly. It is used to mark component values, part numbers, test points, polarity etc.

What is the purpose of using a silkscreen layer?

The silkscreen is not applied to PCB boards by default. A customer has to ask for this and there is usually an additional charge for applying a silkscreen on the board. Here are some important benefits to opt for the silkscreen layer:

• It helps the engineers and technicians identify test points on the PCB board. This way they know where to take measurements from and helps when trouble shooting.
• It can can be used to outline where components need to be placed on the board, this way users will not users forget to place components on the board.
• The silkscreen coating also helps with the warning symbols which are generally used to indicate the higher parameter values such as Voltage, Current and Power.
• It can be used to specify values of inductors, resistors and other components reducing the probability of placing a component with an incorrect value on the board.
• Acts as a reference indicator to identify the component type and polarity orientation.

There are three main ways to add a silkscreen coating on a PCB board:

• Manual screen-printing: This is a process which can be used when line widths are greater than 7 mm and the registration tolerance is 5 mm.
• Liquid Photo Imaging (LPI): This process provides more accuracy and legibility over manual screening and is used when line widths are greater than 4 mm
• Direct Legend Printing (DLP): This is the most accurate way of adding a silkscreen, however it is very expensive.

You can see the quality of the silkscreen based on the approach used in the figure