Whether the quality of PCB ink is excellent, in principle, it is impossible to break away from the combination of the above major components. The ink quality is excellent, which is a comprehensive expression of the scientific, advanced and environmental protection of the formula. It is reflected in:
Viscosity is short for dynamic viscosity. It is generally expressed by viscosity, that is, the shear stress of the fluid flow divided by the velocity gradient in the direction of the flow layer, and the international unit is Pa / s (Pa.S) or mPa.s. In the production of PCB, it refers to the fluidity of ink generated by external force.
Conversion relationship of viscosity unit:
1Pa. S = 10P = 1000mPa. S = 1000CP = 10dpa.s
Plasticity refers to the fact that the ink remains deformed before being deformed by external force. The plasticity of the ink is conducive to improving printing accuracy;
Thixotropic (thixotropic) ink is gelatinous when it is left to stand, and its viscosity changes when it is touched. It is also known as shake resistance and sag resistance.
Fluidity (leveling) The degree to which the ink spreads around under the action of external forces. Fluidity is the reciprocal of viscosity, and fluidity is related to the plasticity and thixotropy of the ink. The plasticity and thixotropy are large, the fluidity is large; the fluidity is large, the imprint is easy to expand. Low fluidity, easy to form netting, and ink formation phenomenon, also known as netting;
Viscoelasticity refers to the ability of the ink that is sheared and broken to rebound quickly after the ink is scraped by the squeegee. It is required that the deformation speed of the ink is fast and the ink rebounds quickly to facilitate printing;
Dryness requires that the ink drying on the screen is as slow as possible, and hope that after the ink is transferred to the substrate, the faster the better;
The size of fineness pigment and solid material particles, PCB ink is generally less than 10μm, the fineness size should be less than one third of the opening of the mesh;
When the ink is picked up with an ink shovel, the degree to which the filamentous ink is stretched without breaking is called stringiness. The ink filament is long, and there are many filaments on the ink surface and the printing surface, which makes the substrate and the printing plate stained, even unable to print;
Ink transparency and hiding power For PCB inks, various requirements are also put forward for the transparency and hiding power of the ink according to the different uses and requirements. Generally speaking, line ink, conductive ink and character ink require high hiding power. The solder resist is more flexible.
The chemical resistance of the ink PCB ink depends on the purpose of use, and the corresponding requirements have strict standards for acids, alkalis, salts, and solvents;
Physical resistance of the ink PCB ink must meet external scratch resistance, thermal shock resistance, mechanical peeling resistance, and meet various strict electrical performance requirements;
The use of ink safety and environmental protection PCB ink requires low toxicity, odorless, safe and environmentally friendly.
Above we have summarized the basic performance of twelve PCB inks, and in the actual operation of screen printing, the viscosity problem is closely related to the operator. The level of viscosity has a great relationship with the silk screen's compliance. Therefore, in the PCB ink technical documents and QC reports, the viscosity is clearly marked, indicating under what conditions, what type of viscosity test instrument, etc.
In the actual printing process, if the ink viscosity is too high, it will cause difficulty in printing, and the edges of the graphics are severely jagged. In order to improve the printing effect, a thinner will be added to make the viscosity meet the requirements. But it is not difficult to find that in many occasions, in order to obtain the ideal resolution (resolution), no matter what viscosity you use, it can never be achieved. Why? After intensive research, it was discovered that ink viscosity is an important factor, but not the only one. There is another quite important factor-thixotropy. It is also affecting the printing accuracy.
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