1. Viscosity and thixotropy

　　In the printed circuit board manufacturing process, screen printing is one of the indispensable important processes. In order to obtain the fidelity of image reproduction, the ink must have good viscosity and suitable thixotropy. The so-called viscosity is the internal friction of the liquid, which means that under the action of external forces, one layer of liquid slides on another layer of liquid, and the friction exerted by the inner layer of liquid. The inner layer of the thick liquid has greater mechanical resistance to sliding, and the thinner liquid has less resistance. The unit of viscosity measurement is poisons. In particular, it should be noted that temperature has a significant effect on viscosity.

　　Thixotropy is a physical property of liquid, that is, the viscosity of the liquid decreases in the state of agitation, and quickly recovers its original viscosity after standing. By stirring, the thixotropic effect lasts long enough for its internal structure to be reconstituted. To achieve high quality screen printing results, the thixotropy of the ink is very important. In particular, during the scraping process, the ink is stirred to make it liquid. This effect speeds up the ink through the mesh and promotes the ink that was originally separated by the network cable to be uniformly connected. Once the scraper stops moving, the ink returns to a static state, and its viscosity quickly returns to the original required data.

　　2. Fineness

　　Pigments and mineral fillers are generally solid, finely ground, their particle size does not exceed 4/5 microns, and form a homogenized flow state in a solid form. Therefore, it is very important to require the ink to have a fine degree.

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