Apr 21, 2021|General
The printed circuit board (PCB) is an essential part of electronic devices. PCBs are green boards with circuitous patterns and markings. The PCB makes all the parts of the device work in harmony.
But what are PCBs made of? They are made of several components. The silkscreen is the topmost layer. The PCB silkscreen is a print layer added to the top of a PCB. The silkscreen print clearly labels the different components of the board. Component labels are the kinds of identification information you will see on the silkscreen.
If a PCB is going to have a silkscreen, the manufacturer will include it during board fabrication. If you ever have to take apart the PCB, the silkscreen will make sure you can assemble it again. The silkscreen will tell the technician or engineer where everything should go and how.
What Is Silkscreen?
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A silkscreen is a layer added to a PCB. It has print that labels the components of the PCB clearly. PCBs don’t come with silkscreens automatically. Silkscreen on a PCB will be applied to the PCB board only if you request it. You will pay an additional charge for a silk screen PCB.
Technicians create a silkscreen with non-conductive epoxy ink. It is applied to the PCB, usually on its component side. When a silkscreen is detailed meticulously, it can be invaluable for manufacturers and engineers. The traditional method for creating a silkscreen involves certain materials. These include a polyester screen that will be stretched over aluminum frames and spray developer, curing ovens and a laser photoplotter.
What Is the Purpose of Using a Silkscreen Layer?
A silkscreen’s purpose lies in its many benefits. With silkscreen print:
- Engineers and technicians can find the PCB’s test points more quickly and easily. This is especially important when taking measurements and troubleshooting.
- You may see warning symbols as well as symbols indicating voltage and current.
- You can use it as a reference indicator. This is useful when identifying polarity orientation and component type.
- You can see where all the components are and should be positioned on the silkscreen PCB easily. This is key to ease of use, especially if you aren’t an expert.
What Information Does a Silkscreen Provide?
A silkscreen provides several kinds of useful information. Silkscreen print helps you identify and understand:
- Warning symbols
- Test points
- Version numbers and manufacturer marks
- Reference designators that facilitate finding parts
- Parts polarity
- The PCB’s model or serial number
- Testing certifications
Methods of Silkscreen Printing
There are three different methods used for applying a silkscreen to the PCB. These are manual screen printing, liquid photo imaging (LPI), and direct legend printing (DLP). Silkscreen application is part of the PCB manufacturing process.
Manual Screen Printing
This method of silkscreen application is useful when there are line widths higher than 0.007” or when there is a 0.005” registration tolerance. This manual screen printing is done by way of a stencil with text and traces. Manufacturers create the latter with nylon. After the PCB silkscreen ink is sent through the stencil to create the silkscreen print, the layer or laminate is put into a baking oven to cure.
Liquid Photo Imaging
The LPI method is appropriate for screen printing when lines exceed 4 mil. How technicians do LPI is extremely similar to the solder mask application. The main difference is that LPI involves coating the laminate with epoxy. Once they do that, they put it under ultraviolet (UV) light for curing. This method gets better accuracy than manual screen printing can achieve. However, LPI uses more ink than other methods. It also takes more time to set up.
Direct Legend Printing
DLP is more expensive than other methods. Acrylic inks and inkjet projectors are necessary for DLP. Computer-aided drawing (CAD) software is utilized to apply ink to the PCB. After that, they use UV light on the ink.
Tips for Silkscreen PCB Design
Including a silkscreen improves the quality of PCB assembly and testing, as well as identification. Below are tips for strong silkscreen PCB designs:
- Be aware that certain fonts don’t do well during the PCB manufacturing process. This is true even with some fonts that software quickly creates. You should use fonts that your CM has approved.
- Stick with black or white and avoid other colors. Which shade you choose should create the most visible contrast with the solder mask color on the board. You cannot see and read the print easily if there isn’t enough contrast.
- Satisfy your CM’s requirements for clearance and dimension. If you don’t do this, components may end up obscuring your silkscreen items. If you cannot see all the items, the silkscreen won’t meet your needs.
- Ensure the silkscreen’s fonts are easy to read. Ask your contract manufacturer (CM) for help in designing effective PCB design guidelines. You should include this in your design for manufacturability (DFM).
- Trying to create a do-it-yourself (DIY) PCB silkscreen is a challenge. You cannot get the same results you would from the manufacturer. Make the silkscreen part of your PCB order. If you delay the silkscreen until later, you will not enjoy all the benefits.
You should want a silkscreen print on a PCB. It tells you the location of all the components, making it easy for you to understand your PCB and how it is assembled. Include a silkscreen in your PCB order. The manufacturer will apply a silkscreen to your PCB. This will be far superior to any kind of DIY PCB silkscreen.
Communicate clearly and consistently with your contract manufacturer if you want the PCB that best fits your requirements and preferences. Tell them that you want a silkscreen from the very beginning and discuss its specifications. Remember to ask them about the extra cost and which process they will use for making and applying the silkscreen. Making sure you will get an effective silkscreen is an important part of planning your PCB.