PCB News - Analysis of the effect of thixotropy on the performance of printed circuit board inks in PCB manufacturing

Analysis of the effect of thixotropy on the performance of printed circuit board inks in PCB manufacturing

In the entire production process of modern PCBs, ink has become one of the indispensable auxiliary materials in the PCB manufacturing process of PCB board factories. It occupies a very important position in the PCB process materials. The success or failure of ink use directly affects the overall technical requirements and quality indicators of PCB shipments. For this reason, circuit board manufacturers attach great importance to the performance of inks. In addition to the well-known ink viscosity, the thixotropy as an ink is often overlooked by people. But it plays a very important role in the effect of screen printing.

Analyze and explore the influence of thixotropy on ink performance in PCB manufacturing:

One, circuit board wire mesh

Circuit board silk screen is one of the indispensable materials in the screen printing process. Without screen, it cannot be called screen printing. Screen printing is the soul of screen printing technology. The screens are almost all silk fabrics (of course there are also non-silk fabrics).

In the PCB industry, the most commonly used is the t-type net. s and hd type networks are generally not used except for individual special needs.

2. Circuit board ink

Refers to colored gelatinous substances used for printed circuit boards. It is often composed of synthetic resins, volatile solvents, oils and fillers, desiccants, pigments and diluents. Often called ink.

Three, several important technical properties of PCB ink

Whether the quality of PCB ink is excellent, in principle, it is impossible to break away from the combination of the above major components. The excellent quality of the ink is a comprehensive manifestation of the scientificity, advancement and environmental protection of the formula. It is reflected in:

⑴Using safety and environmental protection of ink: PCB ink is required to have low toxicity, odorless, safety and environmental protection.

⑵Drying: It is required that the drying of the ink on the screen is as slow as possible, and after the ink is transferred to the substrate, it is required to be as fast as possible.

⑶ Plasticity: It means that the ink still retains its properties before deformation after being deformed by external force. The plasticity of the ink is conducive to improving printing accuracy.

⑷Fineness: the size of pigment and solid material particles, PCB ink is generally less than 10μm, and the size of the fineness should be less than one-third of the mesh opening.

⑸ Chemical resistance of ink: PCB ink has strict standards for acid, alkali, salt and solvent according to different purposes.

⑹ Physical resistance of the ink: PCB ink must meet external scratch resistance, heat shock resistance, mechanical peel resistance, and meet various strict electrical performance requirements.

⑺ Thixotropic: (thixotropic) The ink is gelatinous when standing, and the viscosity changes when touched, also known as thixotropic and sag resistance.

⑻Viscoelasticity: refers to the ability of the ink that is sheared and broken after the ink is scraped by the squeegee to rebound quickly. It is required that the ink deformation speed is fast and the ink rebounds quickly to be beneficial to printing.

⑼ Stringiness: When the ink is picked up with an ink shovel, the degree to which the silk-like ink does not break when stretched is called stringiness. The ink filaments are long, and there are many filaments on the ink surface and the printing surface, which make the substrate and the printing plate dirty and even unable to print.

⑼ Transparency and hiding power of ink: For PCB ink, according to different uses and requirements, various requirements are also put forward for the transparency and hiding power of ink. Generally speaking, circuit inks, conductive inks and character inks all require high hiding power. The solder resist is more flexible.

11. Viscosity: is the abbreviation of dynamic viscosity (dynamicviscosity). Generally expressed by viscosity, that is, the shear stress of fluid flow divided by the velocity gradient in the direction of the flow layer, the international unit is Pa/sec (pa.s) or milliPascal/sec (mpa.s). In the production process of circuit board manufacturers, it refers to the fluidity generated by the external force of the ink.

12. Fluidity: (leveling) the extent to which the ink spreads around under the action of external force. Fluidity is the reciprocal of viscosity, and fluidity is related to the plasticity and thixotropy of the ink. The plasticity and thixotropy are large, the fluidity is large; the fluidity is large, the imprint is easy to expand. The liquidity is small, and it is easy to form netting, resulting in the phenomenon of inking, also known as netting.

Above we have summarized the basic properties of twelve PCB inks. Among them, in the actual operation of screen printing, the problem of viscosity is closely related to the operator. The viscosity is very important to the smoothness of the silk screen. Therefore, in the PCB ink technical documents and qc reports, the viscosity is clearly marked, indicating under what conditions and what type of viscosity testing instrument to use. In the actual printed circuit board process, if the viscosity of the ink is too high, it will be difficult to print out, and the edges of the graphics will be severely jagged. In order to improve the printing effect, a thinner will be added to make the viscosity meet the requirements. But it is not difficult to find that in many cases, in order to obtain the ideal resolution (resolution), no matter what viscosity you use, it is still impossible to achieve. Why? After in-depth research, I discovered that ink viscosity is an important factor, but not the only one. There is another rather important factor: thixotropy. It is also affecting the printing accuracy.