What is the role of PCB ink in the manufacturing process?
The ink plays a role in protecting the copper foil in the production, so that the copper and will not be exposed, which will affect the subsequent processes. There are photosensitive ink, carbon ink and silver ink, and both carbon ink and silver ink have conductivity. The commonly used ink colors are white oil, green oil, black ink, blue ink, red ink and yellow ink.
Most white inks are printed with component and attached marks on FPC, such as secondary tubes.
Black ink is used on a large area on the surface of FPC circuit to strengthen the mechanical strength of FPC.”It can also be used to keep a certain part confidential)
Green ink is used for solder joint, which has insulation effect. It is used on FPC without glue protection.
The important physical properties of ink are viscosity, thixotropy and fineness. These physical properties need to be known to improve the ability of using ink.
Characteristics of PCB ink:
1, Viscosity and thixotropy
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 exerted by the inner liquid when one layer of liquid slides on another layer of liquid under the action of external force.
The mechanical resistance encountered by the inner sliding of thick liquid is large, and the resistance of thinner liquid is small. The unit of viscosity measurement is poise. In particular, it should be pointed out that the temperature has an obvious effect on the viscosity.
Thixotropy is a physical property of a liquid, that is, its viscosity decreases under stirring and quickly returns to its original viscosity after standing. Through stirring, the thixotropy lasts for a long time, which is enough to reconstruct its internal structure.
In order to achieve high-quality screen printing effect, the thixotropy of ink is very important, especially in the process of scraper, the ink is stirred to make it liquid.
This function speeds up the speed of ink passing through the mesh and promotes the ink separated by the original mesh line to be evenly connected into one. Once the scraper stops moving and the ink returns to a static state, its viscosity will quickly return 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 form a homogeneous flow state in solid form. Therefore, it is very important to require the ink to have fineness.
Types of PCB ink:
PCB ink is mainly divided into three categories: circuit, solder resist and legend/mark/component ink.
The circuit ink is used as a barrier to prevent corrosion of the circuit. It protects the circuit during etching. It is generally liquid photosensitive. There are two kinds of acid resistance and alkali resistance. The alkali resistance is more expensive. This layer of ink should be dissolved with alkali after corrosion out of the line.
Solder resist ink is used to protect the circuit after the circuit is finished. There are liquid photosensitive, heat curing and ultraviolet hardening. The pad is reserved on the board to facilitate the welding of components and play the role of insulation and anti-oxidation.
legend/mark/component ink is used to mark the surface of the board. For example, it is usually white.
In fact, there are other inks, such as peelable adhesive ink, which protects the parts that do not need to be treated during copper plating or surface treatment, and then can be torn off; silver paste ink, etc.
Precautions of using PCB ink:
According to the actual experience of most manufacturers in the use of ink, the use of ink must refer to the following provisions:
1, In any case, the temperature of the ink must be kept below 20 – 25. The temperature change cannot be too large, otherwise it will affect the viscosity of the ink and the quality and effect of screen printing.
Especially when the ink is stored outdoors or at different temperatures, it must be placed at the ambient temperature for several days before reuse, or the ink barrel can reach the appropriate operating temperature.
This is because the use of cold ink will cause screen printing failure and cause unnecessary trouble. Therefore, to maintain the quality of ink, it is best to store or store it under normal temperature process conditions.
2, Before use, the ink must be fully and carefully stirred manually or mechanically. If air enters the ink, it must be left standing for a period of time.
If dilution is required, mix it thoroughly first, and then test its viscosity. The ink barrel must be sealed immediately after use. At the same time, never put the ink on the screen back into the ink barrel and mix it with unused ink.
3, It is best to use mutually suitable cleaning agents to clean the net, and it should be very thorough and clean. When cleaning again, it is best to use clean solvents.
4, When the ink is dried, it must have a device with a good exhaust system.
5, To maintain the operation conditions, screen printing shall be carried out at the operation site that meets the process and technical requirements.
