PCB ink refers to the ink used in printed circuit boards (Printed Circuit Board), the important physical properties of which are the viscosity, thixotropy and fineness of the ink. These physical properties need to be known in order to improve the ability to apply ink.
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The characteristics of pcb ink
Viscosity and thixotropy
In the process of manufacturing printed circuit boards, screen printing is one of the indispensable and important processes. In order to obtain the fidelity of image reproduction, the PCB ink must have good viscosity and suitable thixotropy. The so-called viscosity is the internal friction of the liquid, which means that under the action of an external force, one layer of liquid slides on another layer of liquid, and the friction exerted by the inner layer of liquid.
Thick liquid inner layer sliding encounters greater mechanical resistance, and thinner liquid has less resistance. The unit of viscosity measurement is poise. In particular, it should be pointed out that temperature has a significant effect on viscosity.
Thixotropy is a physical characteristic of a liquid, that is, its viscosity decreases under agitation and quickly returns to its original viscosity after standing still. With stirring, the thixotropic effect lasts long enough for its internal structure to be reformed.
To achieve high-quality screen printing effects, the thixotropy of the ink is very important. Especially during the squeegee process, the ink is agitated and thus liquefied. This effect speeds up the speed of the ink passing through the mesh, and promotes the uniform integration of the ink separated by the original mesh line.
Once the scraper stops moving and the ink returns to a static state, its viscosity quickly returns to the original required data.
accuracy
Pigments and mineral fillers are generally solid, finely ground, the 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 PCB ink to have fineness.
Types of PCB ink
There are three main types of PCB inks
- line
- Solder mask
- character ink
The circuit ink is used as a barrier layer to prevent corrosion of the circuit and protect the circuit during etching. It is generally liquid and photosensitive. There are two kinds of acid corrosion resistance and alkali corrosion resistance, the alkali resistance is more expensive, this layer of ink should be dissolved with alkali after the circuit is corroded.
Solder resist ink is applied to the circuit after the circuit is completed to protect the circuit. There are liquid photosensitive ones, heat-cured ones, and ultraviolet-cured ones. The pads are reserved on the board, which is convenient for soldering components, and plays the role of insulation and anti-oxidation.
Character ink is used to mark the surface of the board, such as marking components and parts symbols, etc., usually white.
In fact, there are other inks, such as: peelable adhesive ink, which is to protect the parts that do not need to be treated during copper plating or surface treatment, and then can be torn off; silver paste ink and so on.
Precautions
According to the actual experience of most manufacturers’ PCB ink use, the following regulations must be followed when using ink:
- In any case, the temperature of the ink must be kept below 20-25°C, and the temperature change should not 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 a few days or the ink tank must reach a suitable operating temperature before use.
This is because the use of cold ink will cause screen printing failures and cause unnecessary trouble. Therefore, to maintain the quality of the ink, it is best to store or store it under normal temperature process conditions.
- Before use, the PCB ink must be fully and carefully stirred by hand or mechanically. If air enters the ink, it should be left to stand for a period of time when it is used. If dilution is required, first mix thoroughly and then check its viscosity. The ink barrel must be sealed immediately after use. At the same time, never put the PCB ink on the screen back into the ink tank to mix with the unused ink.
- It is best to use mutually adapted cleaning agents to clean the net, and it must be very thorough and clean. When cleaning again, it is best to use a clean solvent.
- When the ink is dried, it must be carried out in a device with a good exhaust system.
- To maintain the operating conditions, the screen printing operation should be carried out in an operating site that meets the technical requirements of the process.
What role does it play in the process
Ink plays a role in protecting the copper foil during production, so that the copper skin is not exposed outside, which will affect the subsequent processes. There are photosensitive ink, carbon oil, and silver oil, and both carbon oil and silver oil have conductivity. The available ink colors are white oil, green oil, black oil, blue oil, red oil, and butter.
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