Discussion on the Improvement of Printed Screen Printing Precision (I)

I. INTRODUCTION The screen printing process has been widely used in the production process of printed boards. It is not only the transfer of the circuit patterns of single-plane, double-plane and multi-layer printed boards, but also solder resists, character marks, etc. Web printing process. With the development of economy and technology, it is increasingly required to improve product accuracy and qualification rate, ensure product quality and reduce costs, so as to achieve better economic benefits. In recent years, fine lines have also been produced using screen printing processes and require high positional accuracy. Based on my experience in screen printing, this article analyzes several factors that affect the printing screen printing accuracy in the screen printing process, and offers some ideas on how to improve the accuracy for joint discussion.
Second, the factors affecting the screen printing accuracy Printed board graphics printing accuracy, including the following two aspects: First, refers to the printing of the graphics line width distortion is small, line width accuracy ± 0.05mm; second refers to the printing position accuracy The requirements are high. When the length of the pattern is within 500mm, the position deviation is <±0.15mm. There are many factors affecting the accuracy of the above two aspects. From the screen printing to the graphic printing production process, there are mainly the following factors:
1. The selection of silk screen plate materials and printing materials: including frame material, screen material, mesh number, color and printing material performance;
2. Screen printing equipment, tooling: screen printing machine, positioning fixtures, etc.;
3. Production process: including stretch net, screen plate, printing process, etc.;
4. Working environment conditions: The temperature, humidity and cleanliness of the work site, especially the cleanliness, are important factors affecting product quality;

5. People are the most important factor affecting the quality of the project. The operator must have a high degree of responsibility and high technical quality.
The principle of the influence of the factors of the previous aspects on the precision of printing graphics and the measures and methods for improving the accuracy are discussed here.
Third, improve the quality of the screen template is to ensure the premise of screen printing accuracy Factors affecting the quality of the screen template are photographic manuscript drawing quality, photography, photocopying and photographic negatives dimensional stability. The production of screen templates involves a number of factors such as screen frames, screens and stretch nets, plate making and photosensitive materials.
1. The choice of frame material is generally selected LY12, LF2 and other hard alloy aluminum square tube, size selection width 20mm, thickness 20mm, four corners by argon arc welding or riveting processing. The metal frame has high precision and dimensional stability.
2. The choice of screen material The most commonly used is the nylon mesh and polyester mesh. Nylon mesh is poor in heat resistance, easily deformed by heat after being heated, making the tension non-uniform, affecting the quality of screen printing. Bonding stretch net or screen stencil production should not be high-temperature baking. Polyester mesh has good heat resistance, dimensional stability, and the pattern does not change greatly due to changes in temperature and humidity. In order to ensure the accuracy of screen printing graphics, it is best to use monofilament polyester screen. At the same time, screens with a higher number of meshes, smaller wire diameters, and smaller meshes should be selected. The color of the screens should be yellow or brownish to prevent vignetting.