SMT solder paste printing machine, as a main process equipment of SMT production line, 60% of the defects come from the printing quality, and its importance is self-evident. Do you know the technical knowledge of solder paste printing machine? Now let's talk about the necessary technical knowledge of solder paste printing machine technology.

1. Steel mesh: its main function is to accurately apply solder paste on PCB pad. Its quality directly affects the quality of printing. At present, the manufacturing methods of steel mesh include chemical etching, laser cutting and electroforming.

2. Scraper pressure: refers to the falling depth of the scraper, which is one of the important factors affecting the printing quality. Too small scraper pressure will leave a layer of solder paste on the surface of the steel mesh, which is easy to cause printing defects such as printing molding and bonding. The closed-loop control mechanism system of scraper independent scraper head is adopted around the city.

3. Printing speed: there is a certain relationship between printing speed and scraper pressure. Reducing the speed is equivalent to increasing the pressure. Appropriately reducing the pressure can improve the printing speed.

4. Printing gap: printing gap refers to the distance between steel mesh and PCB, which affects the retention of solder paste on PCB after printing.

5. Angle between the scraper and the steel mesh: the smaller the angle between the scraper and the steel mesh, the greater the downward pressure. It is easy to inject the solder paste into the mesh, but it is also easy to squeeze the solder paste to the bottom of the steel mesh, resulting in solder paste adhesion. The angle between the scraper and the steel mesh is usually 45 ~ 60 °.

6. Pattern alignment: align the optical positioning points of the substrate and steel mesh on the workbench through the camera lens of the automatic solder paste printer, and then fine adjust the substrate and steel mesh to make the substrate pad pattern completely coincide with the steel mesh opening pattern. Industrial grade digital CCD camera is adopted around the city, and four-way coaxial surpassing analog mode is adopted.

Explanation of process elements of SMT solder paste printing machine

1、 Printed circuit board pattern alignment

Align the optical positioning points (mark points) of the base plate and the steel mesh on the workbench through the printer camera, and then conduct x, y Θ Fine adjustment to make the base plate pad pattern completely coincide with the steel mesh opening pattern.

2、 Explanation of the angle between scraper and circuit board during printing

The smaller the angle between the scraper and the steel mesh, the greater the downward pressure. It is easy to inject the solder paste into the mesh, but it is also easy to squeeze the solder paste to the bottom of the steel mesh, resulting in solder paste adhesion. Generally 45 ~ 60 ° At present, automatic and semi-automatic printing machines mostly use 60 °

3、 Input amount of solder paste at one time when SMT solder paste printer is working (rolling diameter of solder paste)

1. The rolling diameter of solder paste ∮ h ≈ 10 ~ 15mm is more suitable.

2. If the rolling diameter ∮ h is too small, it is easy to cause solder paste leakage and small amount of tin.

3. If the rolling diameter ∮ h is too large, too much solder paste can not form rolling movement when the printing speed is constant, and the solder paste can not be scraped clean, resulting in poor printing demoulding, thick solder paste after printing and other poor printing; And too much solder paste is exposed to the air for a long time, which is unfavorable to the quality of solder paste.

4. During production, the operator shall visually check the amount of solder paste on the screen every half an hour, move the solder paste outside the scraper stroke on the screen to the scraper stroke of the screen with a shovel every half an hour, and evenly distribute the solder paste, but cannot shovel it into the opening of the steel mesh.

4、 Pressure of scraper when SMT solder paste printer works

Scraper pressure is also an important factor affecting printing quality. The pressure of the scraper actually refers to the falling depth of the scraper. The pressure is too small and the scraper is not close to the surface of the steel mesh, so it is equivalent to increasing the printing thickness. In addition, too little pressure will leave a layer of solder paste on the surface of the steel mesh, which is easy to cause printing defects such as printing molding, bonding (bridging).

5、 Printing speed of SMT solder paste printer

1. Since the speed of the scraper is inversely proportional to the viscosity of the solder paste, the speed is slower when there is a narrow spacing. If the speed is too fast, the time for the scraper to pass through the steel mesh opening is relatively short, and the solder paste cannot fully penetrate into the opening, which is easy to cause printing defects such as insufficient solder paste forming or missing printing.

2. There is a certain relationship between printing speed and scraper pressure. Reducing the speed is equivalent to increasing the pressure. Appropriately reducing the pressure can improve the printing speed.

3. The ideal scraper speed and pressure should just scrape the solder paste from the steel mesh surface.

6、 Printing gap of SMT solder paste printer

The printing gap is the distance between the steel mesh and the PCB, which is related to the retention of solder paste on the PCB after printing.

7、 Separation speed of steel mesh and PCB when SMT solder paste printer works

After solder paste printing, the instantaneous speed of the steel mesh leaving the PCB is the separation speed, which is a parameter related to the printing quality. It is very important in dense spacing and high-density printing. For advanced printing machines, when the steel mesh leaves the solder paste pattern, there is one (or more) small residence process, that is, multi-stage demoulding, which can ensure better printing molding.

When the separation speed is too high, the adhesive force of the solder paste is reduced and the cohesion between the solder paste and the pad is small, which makes some solder paste stick to the bottom surface of the steel mesh and the opening wall, resulting in printing defects such as less printing and tin collapse.

When the separation speed slows down, the solder paste has high viscosity and cohesion, which makes the solder paste easy to separate from the steel mesh opening wall, and the printing state is good.

8、 Cleaning mode and frequency of SMT solder paste printer

Cleaning the bottom of the steel mesh is also a factor to ensure the printing quality. The cleaning mode and frequency shall be determined according to the solder paste, steel mesh material, thickness and opening size. (set dry cleaning, wet cleaning, one-time reciprocating, wiping speed, etc.)