Silk screen printing is one of the popular steps in printed circuit board assembly. This method is used to print the solder mask (the green or black coating that covers the exposed copper on a PCB) and the legend (the text and/or symbols that identify the components) on a PCB. Needless to say, the process is important for two main reasons. First, it helps to protect the components on the PCB from damage. Second, it helps to identify the different parts of the PCB, which is important when troubleshooting or repairing an electronic device. There are several types of PCB silkscreen printing methods available, each with its own advantages and disadvantages. The most common method is the stencil method, which is quick and easy, but can be less precise than other methods. The direct printing method is more precise, but can be more time-consuming. Ultimately, the best method for you will depend on your specific needs and preferences.
Types of PCB Silkscreen Printing Methods
There are several different silkscreen printing methods, and each has its own advantages and disadvantages. The most popular silk screen printing methods are the ones that are listed below:
- Manual Screen Printing: Manual screen printing is a process in which a stencil is used to apply an ink or paste onto a PCB. The stencil has a pattern that is created by a mask which is placed on the stencil. The ink or paste is then squeezed onto the stencil and through the mask, onto the PCB. This process is repeated until the entire PCB is covered. Manual printing is a relatively simple and low-cost manufacturing process, making it a popular choice for small-scale production runs. It is also a versatile process, capable of printing a wide range of materials and substrates.
- Liquid Photo Imaging (LPI): Liquid Photo Imaging (LPI) is a printing process that uses a light-sensitive liquid to transfer an image onto a substrate. The LPI process begins by coating the substrate with a light-sensitive liquid. This liquid is then exposed to a light source, which causes it to harden in the exposed areas. The unexposed areas are washed away, leaving the exposed areas as a negative of the original image. LPI is a versatile printing technique that can be used to create great details. It is also a relatively quick and easy process, making it a popular choice for circuit board manufacturing.
- Direct Legend Printing (DLP): Direct Legend Screen Printing (DLP) is a screen-printing technique that can be used to print direct legends like component reference designators, switch settings, test points, part numbers, and version numbers onto PCBs. This technique is often used when space is limited on the PCB and/or when the legend needs to be very small. DLP is a very precise method of screen printing and can produce very crisp and clean results. This type of PCB silkscreen printing has several advantages over traditional screen printing methods. One advantage is that it can print designs with very fine features and intricate details. Additionally, DLP screen printing is less likely to cause defects in the finished product, such as discrepancy in line widths or print quality.
What Information can be Included on PCB Silkscreen
Silkscreen is one of the most important aspects of a PCB. There are generally three types of information that can be included in the silkscreen of a PCB: identifying information, functional information, and aesthetic information. Identifying information is information that is necessary for the function of the PCB, such as the name and value of the components. Functional information is information that helps with the assembly of the PCB, such as pin numbers and soldering points. The other information include;
- Component values for passives
- A pin-1 indicator for ICs
- A reference designator for each component
- Regulatory markings
- Connector pinouts
- Polarity indicators
- Part numbers for the PCBA
- Component outlines
- Serial number, and lot number
- Other information on assembly, testing, installation, or operation of the PCBA
Silkscreen printing is one of the most important steps in the world of PCB manufacturing. It can have a big impact on the quality of the final product. Poorly printed silkscreens can cause problems with solderability and durability. While silkscreen printing may seem like a relatively straightforward process, it is quite complex. This is why it is important to work with an expert like Rigiflex. The company provides PCB silkscreen that best meets the operational requirements of the PCBs. The company specializes in PCB prototypes and small to mid-volume PCBs.