Technology and Characteristics of Inkjet Printing and Traditional Screen Printing

In recent years, the inkjet printing method of characters has excellent flexibility and convenience because it can directly perform digital operations according to data graphics, eliminating the cumbersome screen production process required by traditional screen printing, and is widely used in PCBs. industry. increasingly common. However, because the jet printing method is quite different from the screen printing method, in the process of replacing the traditional screen printing process, corresponding process adjustments may also be involved, so that the jet printing can better serve the manufacture of the company's products. In the process of making PCB characters, it is necessary to explain the characteristics of the inkjet printing method.

01

The principle of inkjet printing

Inkjet printing is to control the piezoelectric crystal component through a certain driving signal, and eject discrete ink droplets from the nozzle of the nozzle.

Since the nozzles of industrial-grade inkjet printing heads are generally only on the order of tens of microns, and a nozzle will consist of thousands of nozzles, the volume ejected by each ink droplet is very small, such as the ink jetted by the nozzles we use. The dot is only 13pL, and the diameter of the ink dots formed on the substrate is generally only 70-80um.

The traditional screen printing method is to pour the viscous ink on the prepared screen, use a scraper to smooth it, and use a certain pressure to make the ink penetrate from the mesh on the screen to the substrate that is attached to the screen. On the top, the desired pattern is formed, and the size of the mesh determines the fineness of the pattern.

02

inkjet printing ink

According to the description of the principle of jet printing, for ink jet printing, the fluidity required by the ink must be very good, that is, its viscosity will be very low, otherwise the ink will not be able to be ejected from the nozzle of the print head. Therefore, the inkjet printing ink we have seen is more suitable to be called ink. Its viscosity is close to that of water, and the viscosity during printing is generally about 10cps.

Compared with the screen printing process, the ink needs to be very viscous, otherwise the ink will easily ooze out from the screen mesh, and if the fluidity is too strong, it will be difficult to control, and the area that should not have ink will be "pressed". The ink penetrates, and the desired printing pattern cannot be obtained. Compared with jet printing ink, the viscosity of common screen printing ink will be 4000-10000cps, which varies greatly.

The huge difference in viscosity between inkjet printing ink and screen printing ink is reflected in the production of PCB characters. We will find that the inkjet printing ink is very sensitive to the surface state of the PCB. If the surface tension of the substrate is slightly different from that of the printing ink, the jetted ink will Ink dots will spread or shrink, affecting print quality. The viscosity of silk screen printing ink is very high, and it will be very "inert" on the PCB substrate, and it is not easy to spread or shrink by itself. This situation is generally caused by the inappropriate pressure and speed of the scraper.

In addition, due to the extremely low viscosity of the inkjet printing ink, the ink composition is very different from the silk screen printing ink, and the whiteness and three-dimensional effect on the PCB substrate are often weaker than the existing silk screen printing ink, and sometimes I feel that the silk screen characters may be clearer under the characters of the same thickness and size, but because the leveling of the ink jet printing ink will be better, the jet printing characters will feel smoother. Here, we should adhere to the IPC character standard - which is clearly discernible by sight - to judge whether the character quality meets the requirements, and we cannot force inkjet printing and silk screen printing to be exactly the same.