70% of the quality problems in SMT process quality are determined by SMT printing process. Whether the printing process parameters of automatic solder paste printer are set reasonably is directly related to the printing quality, which requires SMT operation technicians to understand the parameter debugging technology of automatic solder paste printer

1、 Scraper length

The opening length of steel mesh shall be increased by 30 ~ 50mm on each side. In order to reduce the amount of solder paste and the contact area between solder paste and air, the length of scraper shall be taken as the smaller value. At present, there are more optional scraper lengths of 150mm / 200mm / 320mm for general automatic solder paste printing machines.

2、 Scraper pressure

The scraper pressure and its corresponding scraper lifting stroke are about 0.08mm/kg. The pressure setting range of 150mm scraper is 1kg ~ 2kg, the pressure setting range of 200mm scraper is 1.5kg ~ 2.5kg, and the pressure setting range of 320mm scraper is 2kg ~ 3kg. In order to improve the service life of the steel mesh and scraper of the full-automatic solder paste printer, the scraper pressure is taken as the lower limit. Usually, you only need to scrape the solder paste on the steel net, and it is acceptable to leave an evacuated single particle layer on the steel net. The pressure of the front and rear scrapers can be different depending on the condition of the scrapers.

3、 Printing speed

The setting principle of the printing speed of the full-automatic solder paste printer is to ensure that the solder paste has enough time to miss printing. When the shape of the solder paste missing printing on the PCB pad is incomplete, the printing speed can be appropriately reduced. The smaller the distance between the small component pins on the printed board, the greater the viscosity of the solder paste, and the printing speed needs to be reduced accordingly. On the contrary, it should be increased. The fine spacing less than or equal to 0.5mm is 20mm ~ 45mm / s, and the spacing of common element feet is 40mm ~ 65mm / s.

4、 Cleaning frequency of steel mesh

The cleaning frequency is based on the tightness of the IC. The IC with dense feet is easy to accumulate the residue of solder paste. If it is necessary to clean the accumulation in the mesh in time, it is necessary to increase the cleaning frequency. The set value takes a larger value on the premise of ensuring that the steel mesh is wiped clean. The spacing less than or equal to 0.5mm is generally 3 ~ 4cps, and the common spacing is 6 ~ 8cps

5、 Separation speed

In the production process of automatic solder paste printing machine, the appropriate separation speed ensures that the solder paste missing printing maintains a good shape. When setting the separation speed, it is necessary to consider the small component spacing and solder paste viscosity on the printed board. The smaller the component spacing is, the greater the solder paste viscosity is, and the smaller the separation speed is. The setting range of separation speed of elements with spacing less than or equal to 0.5mm is 0.3 ~ 0.8mm/s, and the setting range of separation speed of ordinary spacing is 0.8 ~ 2mm / s.

6、 Separation distance

The separation distance is the thickness of the steel mesh plus a certain margin, which is about 1 ~ 1.5mm. The size of the film removal distance is related to the deformation degree of the steel mesh and the fastening degree of the steel mesh. The setting criterion is to ensure that the solder paste thickness on the pad can be separated normally.