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On the advantages of SMT solder paste printer

Time : 2020-04-22

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On the advantages of SMT solder paste printer

In industrial production, there are many factors that affect the printing quality of automatic solder paste printers. Let's take a look at the following main factors.

 Squeegee pressure

The change of squeegee pressure has a great impact on printing. Too small a pressure will prevent the solder paste printer from reaching the bottom of the opening of the stencil and depositing it on the pad well. As a result, the solder paste is printed too thin and may even damage the stencil. The ideal state of the automatic solder paste printer is to scrape the solder paste off the surface of the screen, and the hardness of the scraper of the automatic solder paste printer will also affect the thickness of the solder paste. A too soft doctor blade (composite doctor blade) will sag the solder paste. It is recommended to use a harder doctor blade or a metal doctor blade for fine-pitch printing as shown in the automatic solder paste printer.

(2) Printing thickness

The printing thickness of the automatic solder paste printer is determined by the thickness of the screen. Of course, the automatic solder paste printer has a certain relationship between the setting of the machine and the characteristics of the solder paste. Squeegee pressure to achieve. Properly reducing the printing speed of the blade can increase the amount of solder paste printed on the printed board. One thing is obvious: reducing the speed of the blade is equivalent to increasing the pressure of the blade. On the contrary, increasing the speed of the blade is equivalent to reducing the pressure of the blade.

 Printing speed

The speed of the scraper is good for the rebound of the stencil, but at the same time it will hinder the transfer of solder paste to the pad of the printed board. It has a great relationship with the viscosity of solder paste. The slower the scraper speed, the greater the viscosity of solder paste; Similarly, the faster the scraper speed, the smaller the viscosity of solder paste. Usually the printing speed range for fine pitch is around 25mm / s.


(4) Printing method

The printing method of solder paste can be divided into on-contact and off-contact printing. The printing between the screen and the printed board with a gap is called non-contact printing. When the machine is installed, This distance is adjustable, the general gap is 0-1.27mm; and the printing method of solder paste printing without printing gap (that is, zero gap) is called contact printing. The vertical printing of the contact printing screen can raise the printing quality The least affected, it is especially suitable for the printing of fine and difficult solder paste.

(5) Scraper parameters

The parameters of the squeegee include the material, thickness and width of the squeegee, the elastic force of the squeegee relative to the blade holder, and the angle of the squeegee to the stencil. These parameters affect the distribution of solder paste to varying degrees, where the angle of the squeegee relative to the stencil When θ is 60 ° -65 °, the quality of solder paste printing is the best. When printing, the relationship between the opening size and the direction of the squeegee must be considered. The traditional printing method of solder paste is that the squeegee runs at a 90 ° angle along the x or y direction of the stencil, which often results in the amount of solder paste in different directions of the device opening. Differently, it has been experimentally verified that the thickness of the solder paste scraped when the length of the opening is parallel to the direction of the scraper is about 60% greater than the thickness of the solder paste scraped when the two are perpendicular, and the scraper is printed in the direction of 45 °, which can be obvious Improve the unbalance phenomenon of solder paste in the opening direction of different stencils. At the same time, it can reduce the damage of the scraper to the openings of fine-spaced stencils.

(6) Screen cleaning

During the production process, the cleaning method and frequency of the stencil will directly affect the quality of the printing. It is recommended to use a combination of alcohol cleaning and blowing with compressed air to clean the stencil. The method is: generally in the production of 10 After the PCB, the stencil should be cleaned, first use a clean gauze dipped in an appropriate amount of alcohol for two-side wipe test, then use an air gun to blow up from the bottom (otherwise it is easy to contaminate the PCB), and finally use a dry cloth to wipe clean The problem is that alcohol should not be used too much, otherwise a small amount of alcohol will remain at the bottom of the stencil, which will infiltrate the PCB pads when in contact with the PCB, which will reduce the adhesion of the pads to the solder paste and cause too little printed solder paste. Also note that the air pressure should not be too large, otherwise it will easily cause deformation of the QFP pin opening.


(7) Demoulding speed


The separation speed of the printed board and the screen board will also have a greater impact on the printing effect. If the time is too long, it is easy to leave solder paste on the bottom of the stencil. The time is too short, which is not conducive to the standing of the solder paste and affects its clarity.