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HomeNewsSolve PCB heat dissipation techniques and methods

Solve PCB heat dissipation techniques and methods

2019-06-27

Whether or not the PCB ink quality is excellent is in principle impossible to separate from the combination of the above major components. The excellent ink quality is a comprehensive manifestation of the formula's scientificity, advanced nature and environmental protection. It is reflected in:

Viscosity 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, the fluidity of 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 inks are colloidal when they are left standing, and they are also known as thixotropy and sag resistance when they are exposed to changes in viscosity.

The degree of fluidity (leveling) ink spreading to the surroundings under external force. 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 property that the ink is quickly rebounded by shearing the broken ink after the squeegee is scratched. It is required that the ink be deformed quickly, and ink rebounding can be used to facilitate printing.

Dryness requires the ink to dry on the screen slower the better, and hope that the ink is transferred to the substrate, the faster the better;

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

When the drawability draws ink from the ink scoop, the extent to which the filamentous ink stretches without breaking is referred to as drawability. 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 application 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 inks have strict standards for the requirements of acids, alkalis, salts, and solvents, depending on the purpose of use;

The physical properties of the ink

PCB inks must be resistant to external scratches, thermal shocks, mechanical peeling, and a variety of stringent electrical performance requirements.

The use of ink safety and environmental protection

PCB inks require 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 documentation and QC report, the viscosity is clearly marked, indicating under what conditions, what type of viscosity testing equipment and so on.

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 - thixotropy. It is, it also affects the printing accuracy.

Next: Application of MES System Based on Dynamic Quality Control in PCB Board Assembly Industry