The PCB ink plays a role in protecting the copper foil during production, so that the copper skin will not be exposed, which will affect the subsequent processes. There are photosensitive ink, carbon oil, and silver oil, and carbon oil and silver oil have conductivity. The PCB ink colors are white ink, green ink, black ink, blue ink, red ink and butter ink.

White ink: Most of the characters and attached numbers are printed on the FPC, such as diodes.

Black ink: used on a large area on the surface of the FPC circuit board to enhance the mechanical strength of the FPC. (There are also some parts to keep secret)

Green ink: It is used in the solder joints to have an insulating effect. Generally, there is no glue protection when used on the FPC.

The important physical properties of ink are its viscosity, thixotropy and fineness. These physical properties need to be known to improve the ability to use ink.

Characteristics of ink

1. Stickiness and thixotropy

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

The so-called viscosity is the internal friction of the liquid, which means the friction force exerted by the inner liquid when one layer of liquid slides on another layer under the action of external force.

The mechanical resistance of the thick liquid inner layer sliding is greater, and the thinner liquid has less resistance. The unit of viscosity measurement is poise. In particular, it should be noted that temperature has a significant effect on viscosity.

Thixotropy is a physical property of a liquid, that is, its viscosity decreases under agitation, and it quickly restores its original viscosity after standing still. Through stirring, the effect of thixotropy lasts for a long time, enough to restructure its internal structure.

To achieve high-quality screen printing effects, the thixotropy of the ink is very important. Especially in the process of squeegee, the ink is agitated to make it liquefied.

This function accelerates the speed of ink passing through the mesh, and promotes the uniform connection of the ink separated by the original mesh. Once the squeegee stops moving, the ink returns to a static state, and its viscosity quickly returns to the original required data.

2. Fineness

Pigments and mineral fillers are generally solid. After fine grinding, their particle size does not exceed 4/5 microns, and forms a homogeneous fluid state in a solid form. Therefore, it is very important to require ink to have fineness.

Types of PCB ink

PCB inks are mainly divided into three types: circuit, solder mask, and character ink.

1. The circuit ink is used as a barrier layer to prevent corrosion of the circuit, and to protect the circuit when etching, usually liquid photosensitive type. There are two types of acid corrosion resistance and alkali corrosion resistance. The alkali resistance is more expensive. After the ink is corroded out of the circuit, it must be dissolved with alkali.

2. The solder mask ink is used to protect the circuit after the circuit is completed. There are liquid photosensitive ones, thermal curing ones, and ultraviolet hardening ones. The pads are reserved on the board to facilitate the soldering of components and serve as insulation and anti-oxidation.

3. The character ink is used for marking on the surface of the board, such as those marked with component symbols, which are generally white.

In fact, there are other inks, such as: peelable glue ink, which protects the parts that do not need to be treated during copper plating or surface treatment, and then can be removed; silver paste ink, etc.

Precautions for PCB ink use

According to the actual experience of PCB ink used by most manufacturers, the following regulations must be followed when using PCB ink:

1. In any case, the temperature of the PCB ink must be kept below 20-25°C, and the temperature cannot change too much, otherwise it will affect the viscosity of the PCB ink and the quality and effect of screen printing.

Especially when the PCB ink is stored outdoors or at different temperatures, it must be placed in the ambient temperature for a few days before use or the PCB ink tank can reach a proper operating temperature.

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

2. The PCB ink must be fully and carefully mixed manually or mechanically before use. If air enters the ink, let it stand for a period of time when using it.

If you need to dilute, you must first mix thoroughly, and then check its viscosity. The PCB ink tank must be sealed immediately after use. At the same time, never put the PCB ink on the screen back into the ink tank and mix with the unused ink.

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

4. When the PCB ink is dried, it must be carried out in a device with a good exhaust system.

5. In order to maintain the operating conditions, screen printing should be performed at the operating site that meets the technological requirements.