What is the role of ink in making PCB

Properties of ink

1. Viscosity and thixotropy

In the printed circuit board manufacturing process, screen printing is one of the necessary important processes. In order to obtain the fidelity of image reproduction, the printing ink must have good viscosity and appropriate thixotropy.

Viscosity is the internal friction of a liquid, indicating the friction exerted by an external force that makes a liquid slide over another liquid.

Thicker liquid inner layer sliding encountered greater mechanical resistance, thinner liquid resistance is less. Viscosity is measured in poises. In particular, temperature has a marked effect on viscosity.

Thixotropy is a physical property of a liquid, that is, its viscosity decreases in the stirred state, and soon returns to its original viscosity after standing. By stirring, the thixotropic effect lasts long enough to cause the internal structure to be rebuilt.

In order to achieve high quality screen printing, thixotropy of ink is very important. In particular, in the scraping process, the ink is agitated to liquidate it.

This role to accelerate the speed of ink through the mesh, promote the original wire separated ink evenly connected. Once the scraper stops moving, the ink returns to a static state, and the viscosity quickly returns to the original required data.

2. Fineness

Pigments and mineral fillers are generally solid, finely ground, with particles no larger than 4/5 microns in size, and form a homogeneous flow state in solid form. Therefore, the requirement of ink fineness is very important.

Type of PCB ink

PCB ink is mainly divided into three lines, solder resistance, character ink three categories.

Line ink is used as a barrier layer to prevent corrosion of the line, etching to protect the line, generally liquid photosensitive type. There are two kinds of acid corrosion and alkaline corrosion resistance, alkali resistance is more expensive, this layer of ink in the corrosion line after the use of alkali to dissolve.

Soldering ink is painted on the line as a protection line after the line is done. There are liquid photosensitive and thermal curing, as well as ultraviolet hardening type, reserved pads on the board, convenient welding components, insulation and oxidation prevention.

Character ink is used to do the labeling of the surface of the board, such as marking the symbols of components, generally white.

In fact, there are other ink, such as: peeling ink, is in the copper plating or surface treatment do not need to deal with the part of the protection, and then can be torn off; Silver paste ink, etc.

Note the use of ink

According to the practical experience of the use of ink by most manufacturers, the use of ink must be carried out in accordance with the following provisions:

1, in any case, the temperature of the ink must be kept below 20-25℃, the temperature change can not be too big, otherwise it will affect the viscosity of the ink and screen printing quality and effect.

In particular, when the ink is stored outdoors or at different temperatures, before use, it must be placed in the ambient temperature to adapt to a few days or make the ink barrel to reach the appropriate temperature.

This is because the use of cold ink will cause screen printing failure, causing unnecessary trouble. Therefore, to maintain the quality of the ink, it is best to store or store in normal temperature process conditions.

2, before use must be fully and carefully on the ink manual or mechanical stirring evenly. If the ink into the air, use to stand for a period of time.

If dilution is required, mix it thoroughly first and then check for viscosity. The ink drum must be sealed immediately after use. At the same time do not put the screen ink back to the ink barrel and unused ink mixed together.

3, it is best to use mutually adaptable cleaning agents to clean the net, and to be very thorough and clean. When cleaning again, it is best to use a clean solvent.

4, ink drying, must have a good exhaust system in the device.

5, to keep the operating conditions should meet the technical requirements of the site for screen printing operations.