Things You Must Know About PCB Screen Printing

　Printed circuit boards are an important part of electronic circuits. Over the years, their size has shrunk considerably due to technological advancements. Today, they appear as chips that open up electronic devices. Although printed circuit boards may have multiple components needed to make connections, they may also carry information. Now you might be thinking, how does information get printed in a small area? That's where screen printing comes to the rescue. This article will give you the importance of screen printing on printed circuit boards.

　　Overview of PCB silkscreen layer

　　Silkscreen is a layer of ink traces used to identify PCB components, marks, logos, symbols, etc. If you see, a PCB consists of two parts - components and soldering. In most cases, silkscreen is applied to the component parts of the PCB. Today, it is also used in welded parts. Screen printing helps manufacturers and engineers easily identify different parts.

　　Typically, non-conductive epoxy inks are used for screen printing. The formulation of this ink is different from ordinary printing inks. In most cases, yellow, white and black are used for screen printing. There are certain standard fonts used for PCB software screen printing; however, you can also use custom fonts.

　　What information does silkscreen provide?

　　Silkscreen may not play any role in the function of a PCB; however, its value lies in the information it provides. For example, it will help anyone:

　　Understanding Warning Symbols

　　Part Polarity

　　Identify test points

　　Locate parts by reference marks

　　Identifies a number unique to the printed circuit board.

　　Identify manufacturer marks, version numbers, etc.

　　Screen printing method

　　Silkscreen is applied to PCBs in three ways:

　　1. Manual screen printing:

　　This is done for PCBs when the registration tolerance is 0.005" or the line width is greater than 0.007". Manual screen printing is done using a stencil containing text and traces. The traces are made of nylon. The ink is guided through the stencil onto the layer or laminate. Next, the ink is cured in an oven. This is one of the easiest ways to create silkscreen layers, and it also supports large text sizes. Perfecting the art can take years.

　　2. Liquid Photo Imaging (LPI):

　　This method is used for screen printing lines larger than 4 mils. The process of LPI is almost the same as solder mask application. In this method, however, the laminate is coated with epoxy and then exposed to UV light. The board is cured and developed after it. This method ensures higher precision than manual screen printing.

　　LPI uses white and requires more ink than the other two screen prints. This type of printing takes a long time to set up.

　　3. Direct Legend Printing (DLP):

　　This is one of the most expensive of the other three processes. In the process, inkjet projectors and acrylic inks were used. Ink is applied to the PCB using CAD software. The ink is then exposed to UV light. Acrylic links are not suitable for PCBs that may have a silver finish.

　　Factors to keep in mind when designing silkscreen for your PCB

　　Did you know that silk screen printing accounts for 12-15% of the total cost of a PCB? Text design includes character width, height, thickness, spacing and positioning. Ink costs depend on the screen printing method you choose. Manual screen printing uses epoxy inks and DLP uses acrylic inks. The color and properties of the ink are color influencing factors.

　　Here are some things to consider when designing a PCB with a silkscreen legend.

　　So the next time you're choosing screen printing for your PCB, it's important to make the right choice.

　　You must try to limit the silkscreen to one side. This will help you cut costs in half. Many PCB assembly services charge for double-sided PCB printing.

　　Use standard colors and large shapes to make silkscreen stand out. You can also check to see if the manufacturer offers any special types of ink.

　　Direct Legend Printing (DLP) and Liquid Photo Imaging (LPI) are more expensive than other equipment because their setup requires a higher investment.