Waht are Properties and Types of PCB Ink?

I Concept

PCB ink refers to the ink used in printed circuit board (PCB). Its important physical properties are viscosity, thixotropy and fineness. Mastering the three physical properties could help you better use the ink.

In the production of PCB, the ink is used to protect the copper foil, so that the copper skin is not exposed. There are photosensitive ink, carbon oil, silver oil, and carbon oil and silver oil have electrical conductivity. usually the colors of the ink are white, green, black, blue, red and yellow.

　

PCB Ink

II Properties

1. Viscosity and Thixotropy

Screen printing is one of the most important processes in the manufacture of PCB boards. In order to obtain the fidelity of image reproduction, the ink must have good viscosity and suitable thixotropy.

Viscosity is the internal friction of the liquid, indicating the friction of the inner layer of liquid that makes one layer of liquid slides on the other layer of liquid under the action of an external force. The thick liquid will meet greater mechanical resistance than thin liquid when slides on the inner layer. The unit of viscosity measurement is Pa.s. It should be noticed that the temperatures has a significant effect on viscosity.

Thixotropy is a physical property of liquid. When we stir the liquid, its viscosity decreases but quickly restored after standing for a while. To achieve high-quality screen printing, the thixotropy of the ink is very important. Especially during the scraping process, the ink is agitated and liquefied, accelerating the speed of the ink flowing through the mesh and promoting the fusion of the ink separated by cables. Once we stop scraping , the ink returns to a stationary state and its viscosity quickly restores to the original value.

2. Fineness

Pigments and mineral fillers are generally solid. After finely ground, they have a particle size of no more than 4/5 microns, and enter in a homogenous flow state with solid forms. Therefore, fineness is a very important characteristic of ink.　　

II Types of PCB Ink

PCB Ink is mainly divided into three types: line ink, solder resist ink, and character ink.

1. Line Ink

It is used as a barrier to prevent corrosion of the circuit, which is generally photosensitive in liquid. There are mainly 2 kinds of line ink: acid resistance type and alkali resistance type. Types of alkali resistance is more expensive.

2. Solder Resist Ink

It is used as a protection circuit on the line after the circuit is completed with the function of insulation and anti-oxidation. There are generally 3 types of solder resist ink: liquid-photosensitive type, heat-curing type, and UV-curing type.  

3. Character Ink

It’s used to mark on the surface of the board, including the symbol of the component, usually white.

In fact, there are other ink, such as: peelable glue ink, which is used to protect the parts that need no treatment during copper plating or other surface treatment and can be torn off; silver paste ink and so on.

III Matters Needing Attention

The use of PCB ink when using PCB printer must be carried out according to the following provisions:

1. The temperature of the ink must be kept below 20-25ﾟC in any case, and it can change too much or the viscosity of the ink and the quality and effect of screen printing will be affected.

Especially when the ink is stored outdoors or at different temperatures, before put into use, it must be placed at ambient temperature to adapt for a few days, or we could create a suitable operating temperature in the ink tank. Using cold ink will cause troubles in screen printing, so it’s best to store the ink under normal temperature to maintain its quality.

2. The ink must be thoroughly and carefully stirred by hand or machine before use. If there is air in the ink, the ink should stand for a while. And if dilution is needed, first fully mix the ink, and then check for viscosity. The ink tank must be immediately sealed after use. At the same time, don’t put the ink on the screen back into the tank and mix it with the unused ink.

3. It is best to use a compatible cleaning agent to thoroughly clean the net. A clean solvent is also needed during the cleaning.

4. Ink should be dried in a device with a good exhaust system.

5. Screen printing should be performed in the area with the working conditions in line with the technical requirements of the process and perform operation.