What are the factors that affect the printing quality of smt soldering circuit board solder paste?

In general, there are eight main factors affecting the printing quality of smt soldering circuit board solder paste, namely solder paste, PCB, stencil, printing equipment and fixture, printing process, production environment and professional quality of production staff. Template, solder paste and printing process parameter settings are the three main factors that affect the quality of SMT processing solder paste printing.

First, the influence of the template and the scraper on the printing quality of smt soldering circuit board solder paste.

The thickness of the stencil and the size of the opening have the greatest influence on the printing quality of the smt soldering circuit board. Too thick stencil,too large opening size , and excessive amount of solder paste, which will cause bridging connection. Conversely, insufficient amount of solder paste will result in insufficient solder or virtual soldering, the shape of the opening of the stencil and the smoothness of the opening also affect the mold release quality of the SMT solder paste. The specific impacts are as follows:

(1) The outer dimensions and opening shape of the template opening.Whether the shape and size of the opening on the stencil is compatible with the shape and size of the pads on the PCB. Which it is very important for the precision printing of SMT solder paste.

(2) The thickness of the stencil. In general, for a lead pitch of 0.5 mm, stencils with thickness of 0.12 to 0.15 mm are used, a lead pitch of 0.3 to 0.4 mm, and stencils with thickness of 0.1 mm are used.

(3) The influence of the material and hardness of the scraper on the printing quality of SMT processing solder paste. The surface roughness of the solder paste is different, and the degree of digging of the solder paste is different. The metal scraper is much smaller than the polyester scrapper in digging aspect. The thickness of the metal scrapper paste is much closer to the actual thickness of the stencil than the polyester scrapper.

The effect of solder paste on the quality of solder paste printing.

(1) The viscosity of the solder paste. The viscosity of the solder paste is an important factor affecting the printing performance of the smt soldering circuit board. The viscosity is too large, the solder paste is not easy to pass through the opening of the template, and the printed lines are incomplete; the viscosity is too small, and it is easy to flow and collapse. Affecting the resolution and line flatness of SMT printing, and the paste viscosity can be measured with a precision viscometer.

(2) The viscosity of the solder paste. The solder paste is not sticky enough. The solder paste does not roll on the template during SMT printing. The direct result is that the solder paste cannot completely fill the template opening, resulting in insufficient deposition of solder paste. Too much viscosity of the solder paste will cause the solder paste to hang on the wall of the template hole and not be completely printed on the pad.

(3) Uniformity and size of solder paste particles. The shape, diameter and uniformity of the solder particles in the solder paste also affect the printing performance.

(4) Metal content and thixotropic index of solder paste. The amount of metal in the solder paste determines the thickness of the solder after soldering. As the percentage of metal increases, the thickness of the solder also increases. However, at a given viscosity, as the metal content increases, the tendency of solder bridging increases accordingly.

Third, The impact of smt soldering circuit board SMT processing printing process parameters on the quality of solder paste printing. The parameters such as scrapper pressure, printing speed, printing stroke, scrapper parameters, separation speed, and template cleaning have a great influence on the quality of solder paste printing. This can be showed in the setting of the previous printing process parameters.

SMT solder paste printing quality is more likely to test the strength and ability of the pcb factory on the smt process and details, including solder paste, scraper preservation, selection, mixing and so on.

The above is the industry information provided by FASTPCBA., I hope to help you!