Silkscreen printing is an indispensable part of the printed circuit board fabrication. If you are new to the field of PCB design and fabrication, you must be wondering about the significance of this printing process. The silkscreen is a layer of ink traces that helps provide text-based, human-readable information of different circuit points, components, and additional circuitry, date codes, testing points, and manufacturer marks, among others. Silkscreen, also known as legend or nomenclature, allows both the manufacturer and the engineer to locate and identify all the components, while also eliminating the chances of errors. How is silkscreen applied to PCBs? There are majorly three methods. Let’s see the methods in brief in this post.
3 Methods of Silkscreen Printing
Being one of the most artistic processes in a PCB manufacturing, the silk-screening process requires specially formulated inks. Almost every silkscreen circuit board manufacturer applies silkscreen through any of the following methods:
Manual Screen Printing: Although it is easy to set up and application, the accuracy level of manual screen printing differs from other techniques mentioned here. Many circuit board manufacturers rue about its perfection. Manual screen printing is applicable for boards with line widths greater than 7 mils (0.007ʺ) , and having registration tolerance of 5 mils. During manual screen printing, a silkscreen circuit board manufacturer considers several factors such as viscosity and age of ink, room temperature and humidity, the pressure of stroke to get the right output, and so on. Major steps involved in manual screen printing are as follow:
- On the stencil of the text, ink is pushed through onto the laminate
- The board is then cured in an oven.
Liquid Photo Imaging (LPI): This method is utilized when the line width is greater than 4 mil. It can produce better accuracy and legibility. LPI, which helps produce the best resolution of images and text, involves the following steps:
- Liquid photo-imageable epoxy is coated on to the laminate
- This laminate is then exposed to UV light
- It is then subjected to the curing process.
Direct Legend Printing (DLP): This is the fastest and the most accurate of all the silk screen printing processes mentioned here. Appropriate for complex printed circuit boards, the DLP silkscreen method involves the following steps.
- Acrylic ink is applied onto the raw PCB utilizing an inkjet projector
- The ink is cured with UV light.
Why is Silkscreening Important?
Silkscreening is used during different phases of PCB manufacturing and assembly. It is mainly used during mounting or placing components. The following are a few silkscreen indicators used to position the components.
- Pin 1 Indicator
- Reference Indicators
- Component Outline
- Polarity Indicators
The silkscreen markings are also used during the inspection and testing phase of the PCB manufacturing. They are used to mark the following:
- Part Numbers
- Test Points
- Warning Symbols
Following these markings enable PCB fabricators to detect component failures, as well as verify the performance of the circuit board.
The whole process of screen printing is not too difficult, but it must be executed carefully to avoid errors. The quality and readability of silkscreen printing is more important than ever with the increasing complexity of today’s boards.