The Fault Analysis And Solution Of PCB Screen Printing Process
In the process of screen printing, various kinds of failures will occur. It will not only affect the production but also affect the quality of screen printing. There are many reasons for the failure, not only related to the operator's screen printing technology, but also related to the properties of printing materials, substrates, screen printing methods, screen quality, and scrapers. If screen printing operators are unfamiliar with the technology and work quality is not high, screen printing failures are likely to occur. Similarly, if printing materials, screens, squeegees, screen printers, and screen printing environments are not good, screen printing failures may also occur.
1. Failure caused by PCB printing
The printing material on the screen plate will block some of the screen meshes, resulting in less or no penetration of the printing material in the portion, resulting in poor printing patterns.
1.1.1 The number of screen meshes does not match the printed material used
The number of screens used is high, and the aperture of the screen is small. However, the size (fineness) of the used printing material is large. When the screen printing is performed, large particles in the printing material block the openings and cause screen failure. The large particles in the print are mainly from the fillers in the print, such as pigments, fluorescents, etc. When gold and silver conductive printing materials and carbon conductive printing materials are used, screen mesh screens should be used because of their large particle size.
1.1.2 Printing material get dry on the screen
The solvent in the printing material is dried in the screen printing process due to volatilization caused by the environment. For this kind of situation, according to the temperature and humidity conditions of the working environment, choose the appropriate printing thinner to control the drying speed of the printing material.
1.1.3 printing material viscosity
The printing material has large viscosity, strong viscoelasticity, and poor fluidity, so that the printing material has poor permeability during screen printing, and is easy to produce plugging holes. In general, to reduce the viscosity, additives or diluents are added to the printing material, which can be used after sufficient stirring.
1) Clean the screen Carefully;
2) Re-experience printing materials to confirm whether they can continue to use.
1.2 Printed Board Contamination on the Reverse Side
As the printed film on the printed board is not yet completely dry, the printed boards are stacked together, so that the printed material adheres to the reverse side of the printed board and causes contamination, for example, when an oxidized polymeric printed material is to be used Due to the stacking of the printed board itself, the surface of the printed coating is broken, so that the incompletely cured printing material of the coating film adheres to the opposite side of the printed board and causes contamination.
1.3 Poor adhesion
A wide range of screen printing can be printed on various materials. Therefore, there are many factors that cause poor adhesion.
1.3.1 PCB Advantages Cause Bad Bonding
The pre-treatment of the printed board has a great influence on the bonding strength. If the pre-treatment is poor, the bonding failure will result. There are many methods for pretreatment, and it is not easy to use the naked eye to check the quality of the treated surface. The wettability test can be used to determine the effect of the treatment.
1.3.2 The selected printing material does not match the substrate
The appropriate printing materials should be selected according to the properties of the substrate materials and screen printing requirements. Before running, the quality of substrate materials and the surface treatment conditions should be tested to determine the selected printing materials.