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Elements of solder paste printing process-Ⅰ Written by HC AUTOMATOIN / Read 302 times

A. Graphic alignment of printed circuit boards

The optical positioning points (Fiducial MARK points) of the base plate and the stencil on the worktable are aligned by the printer camera, and then the X, Y and angle  of the base plate and the stencil are precisely adjusted, so that the pattern of the base plate welding pad and the pattern of the stencil opening are completely coincided. 


B. Explanation of the angle between squeegee and circuit board in printing

The smaller the angle between the squeegee and the stencil is, the greater the downward pressure is. Simply inject the solder paste into the stencil hole, but also simply squeeze the solder paste to the bottom of the stencil to form solder paste adhesion. At present, automatic and semi-automatic printing presses mostly use 60 degrees.

C. Input of solder paste in SMT solder paste screen printer machine (roll diameter of solder paste)

1. The rolling diameter of solder paste D =10-15 mm is suitable. 

2. Too small rolling diameter h is easy to make solder paste leak and less tin. 

3. Too much solder paste can not form roll motion and squeegee cleanliness when the roll diameter is too large. Too much solder paste is exposed to air for a long time, which is harmful to the quality of solder paste.

4. In production, the operator inspects the amount of solder paste on the mesh every half hour visually, moves the solder paste beyond the scraper stroke on the mesh every half hour to the scraper stroke of the mesh plate with a spade and distributes the solder paste evenly, but cannot shovel the solder paste into the opening of the steel mesh.

D. Pressure of squeegee in operation of SMT solder paste screen printer

Scraper pressure is also an important factor affecting printing quality. The practice of scraper pressure refers to the depth of the scraper's descent, the pressure is too small, the scraper does not adhere to the appearance of the steel mesh, thus equivalent to increasing the printing thickness. Other pressures are too small to leave a layer of solder paste on the surface of the steel mesh, which simply constitutes printing defects such as bonding (bridging).