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Advantages of scraper system for SMT printing machine

Advantages of scraper system for SMT printing machine

Solder paste is used to print on PCB board in SMT, one of the processes is to use a scraper to squeeze the solder paste and transfer the solder paste from stencil to PCB board.Next, what are  advantages of the printing scraper system introduced by PCBA factory engineer?

The scraper system is the most complex moving mechanism in the printing machine, including the scraper fixing mechanism and scraper transmission control system.

The function of the scraper system: the solder paste is expanded into a uniform layer on the entire template area. The scraper presses on the template to make the solder paste contact with PCB;The scraper pushes the solder paste on the template forward and fills the opening of the template at the same time;When the stencil is removed from the PCB, leave a suitable thickness of solder paste on the PCB corresponding to the stencil pattern.

The scraper has the metal scraper and the rubber scraper and so on, applies in the different occasion respectively.It must have high friction resistance and solvent resistance, and its hardness is an important factor which affect the quality of solder paste printing.Too large pressure of scraper head or too soft material, the auxiliary knife made of rubber is easy to be embedded into the hole of the metal template (especially the big window hole), and the solder paste in the hole is extruded, thus resulting in the sunk of printed graphics and bad printing effect.Thus, people use metal scraper instead of rubber vice – knife.Metal scraper is made of high hardness alloy so that it is very resistant to fatigue, wear and bending, and coated with lubricating film on the blade.Solder paste can be easily pushed into the window when the blade is running on the template, eliminating the defects and fluctuation of solder.

In addition, a new type of closed seal blade technology has appeared in recent years.Compared with the open type scraper described above, it has the following advantages.

1) solder paste can be printed with very little amount of solder paste.

(2) it is beneficial to prevent the oxidation of solder paste.

(3) high effective utilization rate of solder paste.

(4) internal pressure to strengthen the solder paste filling effect, to prevent the happening of printing defects.

(5)more simple craft modulation, faster printing speed.

However, the closed blade is very expensive and only improves the printing problem partly, so it is not used widely.