Viscosity
It is short for dynamic viscosity. Viscosity is generally expressed as the shear stress of the fluid flow divided by the velocity gradient in the flow layer direction, and the international unit is pa/s (pa.s) or milli-pascal/sec (mpa.s). In pcb production, it refers to the fluidity that the ink is driven by external forces.
Conversion of viscosity units:
1pa. s=10p=1000mpa. s=1000cp=10dpa.s
plasticity
Refers to the nature of the ink before it is deformed after the ink is deformed by external forces. The plasticity of the ink helps to improve the printing accuracy;
Thixotropic
When the ink is in a gel state when it is left standing, it has a property that the viscosity changes when it is touched. It is also called thixotropy and sag resistance;
fluidity
(Leveling) The extent to which the ink spreads out under the action of external forces. Fluidity is the reciprocal of the viscosity, which is related to the plasticity and thixotropy of the ink. Plasticity and thixotropy are large, and fluidity is large; when the fluidity is large, the imprinting is easy to expand. Small liquidity, prone to netting, resulting in ink phenomenon, also known as reticulate;
Viscoelasticity
Refers to the ink's ability to snap back and snap back when the squeegee prints. It is required that the ink be deformed quickly, and ink rebounding can be used to facilitate printing.
Dryness
It is required that the slower the ink dries on the screen, the better, and the faster the ink is desired, the better it is to transfer the ink to the substrate.
Fineness
The size of pigment and solid material particles, pcb ink is generally less than 10μm, the size of fineness should be less than one-third of the opening of the mesh;
Drawing property
　　 When the ink is picked up with an ink scoop, the degree of stretching of the filamentous ink without breaking is referred to as stringiness. The ink is long and there are many filaments on the ink surface and the printing surface, which make the substrate and the printing plate dirty, and even unable to print;
Ink transparency and hiding power
　　 For pcb inks, various requirements are also made for the transparency and hiding power of the ink, depending on the use and requirements. In general, line inks, conductive inks, and character inks all require high hiding power. The solder resist is more flexible.
Chemical resistance of ink
Pcb ink has strict standards for the requirements of acids, alkalis, salts and solvents, depending on the purpose of use;
The physical properties of the ink
Pbb ink must meet the resistance to external scratches, thermal shock, resistance to mechanical peeling, as well as to meet a variety of stringent 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 among them, 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 silk screen printing. Therefore, in the pcb ink technical file and the qc report, the viscosity is clearly marked, indicating under what conditions, what type of viscosity testing instruments are used. In the actual printing process, if the viscosity of the ink is too high, it will cause difficulty in printing, serious jagged edges in the pattern, in order to improve the printing effect, it will add thinner to make the viscosity meet the requirements. However, it is not difficult to find that in many situations, in order to obtain the ideal resolution (resolution), no matter what viscosity you use, it will never be achieved. why? After in-depth study, it was discovered that ink viscosity is an important factor, but not the only one. There is another quite important factor thixotropic. It is, it also affects the printing accuracy.