Various types of inks used in printed circuit boards have a lot of properties, of which the importance is the viscosity, thixotropy and fineness of the ink. These physical properties need to be known to improve the ability to use inks. one. Ink characteristics 1. Viscosity and thixotropy In the manufacturing process of printed circuit boards, screen printing is an indispensable and important process. In order to obtain the fidelity of image reproduction, it is required that the ink must have good tackiness and appropriate thixotropy. The so-called viscosity is the internal friction of the liquid, which means that under the action of the external force, a layer of liquid slides on the other layer of liquid, and the friction force exerted by the inner layer of liquid. The mechanical resistance to the sliding of the inner layer of the thick liquid is greater, and the resistance of the thinner liquid is smaller. The unit of viscosity measurement is poise. In particular, the temperatures that should be noted have a significant effect on the viscosity. Thixotropy is a physical property of a liquid, that is, its viscosity decreases under stirring and returns to its original viscosity characteristics soon after it is left standing. By stirring, the thixotropic effect lasts long enough to reconstruct its internal structure. To achieve high quality screen printing, the thixotropy of ink is very important. Especially during the squeegee process, the ink is agitated, which in turn liquefies. This action speeds up the speed of the ink passing through the mesh and promotes the uniform separation of the ink from the original wire. Once the squeegee stops moving, the ink returns to a stationary state and its viscosity quickly returns to its original desired data. 2. accuracy: Pigments and mineral fillers are generally solid, finely ground, and their particle size does not exceed 4/5 μm, and they form a homogenous flow state in solid form. Therefore, it is very important to require the fineness of the ink. two. The use of ink precautions According to the practical experience of most manufacturers' ink use, the following guidelines must be followed when using inks: 1. In any case, the temperature of the ink must be kept below 20-25°C, and the temperature change can not be too large, otherwise it will affect the viscosity and screen printing quality and effect of the ink. Especially when the ink is stored outdoors or stored at different temperatures, it must be allowed to stand at ambient temperature for a few days before it is reused or the proper temperature for the inside of the ink bucket is reached. This is because the use of cold ink can cause screen printing faults and cause unnecessary trouble. Therefore, to maintain the quality of the ink, it is best stored or stored under normal temperature process conditions. 2. The ink must be fully and carefully mixed by hand or mechanically before use. If ink gets into the air, leave it for a while. If you need to dilute, first mix thoroughly and then measure its viscosity. The ink tank must be sealed immediately after use. At the same time, never put the ink on the screen back into the ink tank and mix it with the unused ink. 3. It is best to use a compatible cleaning agent for cleaning, and it is very thorough and clean. When cleaning, it is best to use a clean solvent. 4. When the ink is dried, it must be carried in a device with a good exhaust system. 5. To maintain the operating conditions should be in line with the technical requirements of the operation of screen printing operations.
Source: Electronic Circuit Center Technology