Brief Discussion on Several Important Technical Performances of PCB Ink

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Whether the quality of PCB ink is excellent, in principle, it is impossible to break away from the combination of the above several components. The excellent ink quality is a comprehensive expression of the scientific, advanced and environmentally friendly formula. It is reflected in: Viscosity is the abbreviation of dynamic viscosity (dynamicviscosity). 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, the international unit is Pa / sec.

Whether the quality of PCB ink is excellent, in principle, it is impossible to break away from the combination of the above several components. The excellent ink quality is a comprehensive expression of the scientific, advanced and environmentally friendly formula. It is reflected in:

 

Viscosity

It is an abbreviation for dynamic viscosity (dynamicviscosity). Generally expressed in 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 per second (Pa.S) or millipascals per second (mPa.S). In PCB production, it refers to the fluidity generated by the external force of the ink. Conversion relationship of viscosity units: 1Pa. S = 10P = 1000 mPa. S=1000CP=10dpa.s

Plasticity

It means that the ink retains its pre-deformation properties after being deformed by external force. The plasticity of the ink is beneficial to improve the printing accuracy;

 

Thixotropic

The ink is gel-like when it is still standing, and the viscosity changes when it is touched, which is also called shearing and sag resistance;

 

Fluidity

(Leveling) The extent to which the ink spreads around under the action of an external force. Fluidity is the reciprocal of viscosity, which is related to the plasticity and thixotropy of the ink. If the plasticity and thixotropy are large, the fluidity is large; if the fluidity is large, the imprint is easy to expand. The fluidity is small, and it is prone to netting and causing ink sticking, also known as netting;

 

Viscoelasticity

Refers to the performance of the ink which is sheared and broken by the ink after the ink is scraped off. It is required to have a fast deformation speed of the ink, and the ink rebounds quickly to facilitate printing;

 

Dryness

It is required that the drying of the ink on the screen is as slow as possible, and after the ink is desired to be transferred to the substrate, the faster the better;

 

Fineness

The size of the pigment and solid material particles, the PCB ink is generally less than 10μm, and the fineness should be less than one third of the opening of the mesh;

 

Wire drawing

When the ink is picked up with an ink shovel, the degree to which the filament-like ink does not break is called the stringiness. The ink is long, and a lot of filaments appear on the ink surface and the printing surface, so that the substrate and the printing plate are dirty or even impossible to print;

 

Ink transparency and hiding power

For PCB inks, various requirements are also imposed on the transparency and hiding power of the ink depending on the application and requirements. In general, line inks, conductive inks, and character inks all require high hiding power. Solder resists are more flexible.

 

Chemical resistance of ink

PCB inks have strict standards for acid, alkali, salt and solvent requirements depending on the purpose of use;

 

 Physical resistance of ink

PCB inks must comply with external force scratches, thermal shock resistance, mechanical peeling, and meet various stringent electrical performance requirements;

 

Ink safety and environmental protection

PCB inks are required to be low toxic, 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 is extremely relevant to the smoothness of silk screen printing. Therefore, in the PCB ink technical documents and QC report, the viscosity is clearly marked, indicating under what conditions, what type of viscosity test instrument is used. In the actual printing process, if the ink viscosity is too high, it will cause difficulty in printing, and the edge of the pattern is severely serrated. In order to improve the printing effect, a thinner is added to make the viscosity meet the requirements. However, it is not difficult to find that in many cases, in order to obtain the desired resolution (resolution), no matter what viscosity you use, it is always impossible. why? After intensive research, it was discovered that ink viscosity is an important factor, but not the only one. There is another fairly important factor - thixotropy. It is also affecting the printing accuracy.