Essential Insights into PCB Silkscreen Printing

Jan 20,2020

A printed circuit board is an essential part of the electronics circuit. Over the years, owing to advancements in technologies, their size has reduced drastically. Today, they appear as a chip on opening the electronic device. Although a printed circuit board may feature several components required to make a connection, they may also bear information. Now you may think how is information printed in a small area? This is where silkscreen printing comes to rescue. This post will provide you the importance of silkscreen printing on printed circuit boards.

An Overview of Silkscreen Layer of a PCB 

The silkscreen is a layer of ink trace used to identify the PCB components, marks, logos, symbols, and so on. If you see, a PCB comprises two parts – components and soldering. Mostly, the silkscreen is applied to the component part of the PCB. Nowadays, it is also applied to the soldering part. The silkscreen printing helps both – the manufacturer and the engineer to identify different parts easily.  

Typically, non-conductive epoxy ink is used for silk screen printing. This ink has a different formulation than the regular printing inks. Most times, silk screen printing is performed using colors of yellow, white, and black. There are certain standard fonts used by PCB software for silkscreen printing; however, you can also use custom fonts.

What Information Does a Silkscreen Provide?

A silkscreen 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:

• Understand the warning symbols
• Polarity of parts
• Identify the test points
• Locate the parts through reference designators
• Identify the numbers that are unique to the printed circuit board.
• Identify manufacturer marks, version numbers, and so on

Methods of Silk Screen Printing

The silkscreen is applied on the PCB in three ways:

1. Manual Screen Printing:

This is done for PCBs when the registration tolerance is 0.005" or line widths are greater than 0.007". Manual screen printing is performed using a stencil comprising text and traces. The traces are made using nylon. The ink is directed through the stencil on to the layer or laminate. Next, the ink is cured in the baking oven. This is one of the easiest ways of creating a silkscreen layer and it supports large text size, too. It may take years to perfect this art.

2. Liquid Photo Imaging (LPI):

This method is used for screen printing the lines that are greater than 4 mil. The process of LPI is almost the same as the solder mask application. However, in this method, the laminate is coated with epoxy, and then it is brought under the UV light. The board is cured and developed after it. This method ensures higher accuracy than manual screen printing.

LPI uses white color, and it requires more ink than the other two types of silk screen printing. The setup time for this type of printing is high.

3. Direct Legend Printing (DLP):

This is one of the most expensive processes among the other three. During this process, inkjet projector and acrylic inks are used. The ink is applied to the PCB using the CAD software. The ink is then exposed to the UV light. The acrylic link is not suited for the PCBs that may have silver finishes.

Factors to Keep in Mind When Designing Silk Screen for Your PCB

Do you know the silkscreen contributes to 12-15% of the total PCB costs? The text design includes character width, height, thickness, spacing, and positioning. The cost of ink will depend on the method of silkscreen printing you have opted for. Epoxy ink is used in manual screen printing, and acrylic ink is used for the DLP. The color and properties of the ink are the color contributing factor.

The following are a few things to consider when designing the PCB with a silkscreen legend.

So, the next time, when you choose silkscreen printing for your PCB it is important to make the right choices. Knowing the importance of silkscreen printed PCB, it is important that you source it from a trusted manufacturer like Creative Hi-Tech. The company provides the PCB in diverse specifications.

• You must try to restrict the silkscreen to one side only. This will help you cut down the costs to half. Many PCB assembly services charge for two side PCB printing.
• Use standard colors and large shapes to make the silkscreen stand out. You can also check if the manufacturer provides any special types of ink.  
• Direct Legend Printing (DLP) and Liquid Photo Imaging (LPI) more are expensive than the rest because their setup requires a higher investment.      

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