Printing process provides appropriate welding alloy composition for welding. Printer must adjust correctly to ensure proper solder paste precipitation, thus forming a uniform solder paste layer on the surface of PCB to ensure good welding.

1.Scraper stop distance

Scraper stop distance means that the printer controls the stroke of the scraper to prevent excessive downward movement of the scraper and damage to the steel mesh. Generally, it is advisable to adjust the scraper to the surface of the steel mesh just touched.

Sometimes the installation axis of the scraper is not completely parallel to the surface of the steel mesh. At this time, it is necessary to adjust the stop distance of the scraper to compensate, but if the stop distance is too adjusted, the SMT steel mesh and the scraper wear quickly.Some equipment has no stop distance, only the origin of the scraper, usually the scraper has just touched the SMT steel mesh.The pressure of the scraper is applied to the SMT steel net through the spring loading system.

2.Squeegee Pressure

The smaller the scraper pressure is, the better. It is advisable to propel the solder paste to roll on the steel net just cleanly. If properly adjusted, a thin layer of flux will be left on the steel net at the scraper pass. The size of the scraper pressure depends on the printing speed and the size of the steel net. Too small scraper pressure is sometimes more harmful than too large scraper pressure. When scraper pressure is too small, only a thin layer of solder paste will deposit on the steel mesh, while the solder paste at the large opening will be too thick, and the solder paste at the small opening can not deposit on the steel mesh through the steel mesh opening.Parameter Settings: 1-1.5 lbs/inch or 0.5 kg/25mm

3.Printing speed

Often the solder paste manufacturer/supplier will provide the corresponding printing speed window of solder paste. The printing speed of solder paste is generally set between 20 mm/s and 80 mm/s. Printing speed depends on the thixotropic properties of solder paste. The solder paste becomes soft and fluidity increases during printing, but gelatinizes rapidly after passing through the mesh and keeps a certain shape and viscosity for a period of time.The stronger the fluidity of solder paste during rolling, the faster it can be applied.Proper printing speed can give better play to the thixotropic properties and fluidity of solder paste, so that it can roll on the steel network, so as to achieve the perfect solder paste precipitation. Printing cycle in production process is the main factor of production efficiency. It can use faster printing speed without affecting the quality of printing.Printing Speed Settings: 12-40 mm/s

4.Snap off

Snap off refers to the distance between the bottom of the steel mesh and the surface of the printed board when the scraper does not touch the steel mesh in the printing process.Snap off is usually 0 for metal steel mesh, which is commonly referred to as contact printing.Snap off is usually set to 0.5-3.0 mm for wire mesh.Snap off mainly affects the volume of solder paste deposited on the solder pad of PCB.Higher Snap off results in thicker solder paste precipitation

5.Separation speed

It refers to the separation speed of steel screen and printed board after printing, which is very important for the volume and forming of solder paste after precipitation.In the printing of close foot spacing components, too fast separation speed will lead to higher tips and solder paste deposition edges.The ideal separation rate depends on the properties of solder paste and the roughness of the mesh wall. In addition, too slow separation speed will lead to the growth of printing cycle, affecting production efficiency.

6.Printing area/scraper length

In the printing process, in order to ensure that the solder paste rolls correctly before reaching the through hole of the steel mesh, so as to achieve a certain fluidity, the front and back position of the scraper should be far away from the rolling diameter of the solder paste about 80 mm to 100 mm or twice of the open hole of the steel mesh.The left and right position of scraper should be at least 20 mm wider than that of PCB.

7.Stencil mesh cleaning

In theory, if all the printing parameters are controlled, it is not necessary to clean the laser steel mesh.The cleaning of steel mesh can be divided into manual and automatic ways.