How to Set the Processing Parameters of SMT?

In SMT processing, many processes need to be set the parameters of the processing equipment. However, many detailed parameters cannot be achieved overnight. SMT manufacturers need to sum up experience in long-term practice to process high-quality products. The setting steps are mainly divided into the following 7 steps:

 

 

 

1. Graphic alignment

Use the printer camera to align the optical MARK point on the stencil on the workbench, and then fine-tune the X, Y, θ and other graphics to make the stencil and the stencil pad patterns completely match.

 

 

2. Angle of scraper and stencil

The smaller the angle between the scraper and the stencil, the greater the downward pressure. The solder paste can be easily injected into the stencil, and the solder paste can be squeezed into the bottom of the stencil. The angle between the scraper and the stencil is usually 45-60 degrees.

 

 

3. Scraper force

Scraper force is an important factor affecting printing quality. The pressure management of the scraper is actually the depth of the descent of the scraper. If the pressure is too small, the scraper cannot stick to the mesh surface, so it is equivalent to increasing the thickness of the printed material during SMT process. In addition, if the pressure is too small, a layer of solder paste will be left on the screen, which may easily cause printing defects such as molding and bonding.

 

 

4. Printing speed

Since the scraper speed is inversely proportional to the viscosity of the solder paste, if the density of the solder paste is high, the spacing will become narrower and the printing speed will also slow down. If the scraper is too fast, the time for the solder paste to enter the mesh will be shortened, which will lead to the inability to fully penetrate the solder paste into the mesh, and easily cause printing defects such as uneven solder paste and missing printing. The printing speed has a certain relationship with the pressure of the scraper, and the descending speed is equal to the pressing speed. Appropriately reducing the pressing speed can increase the printing speed. The best scraper processing speed and pressure control method is to scrape the solder paste from the surface of the stencil.

 

 

5. Printing gap

The printing gap is the distance between the printed circuit and the circuit, and it is related to the printed solder paste remaining on the circuit board.

 

 

6. Separation speed of stencil and PCB

After the solder paste is printed, the instantaneous speed at which the stencil leaves the PCB is the separation speed. The separation speed is the main factor affecting the printing quality, which is especially important in high-density printing. Advanced SMT printing equipment, there will be a pause when the iron mesh leaves the solder paste pattern, that is, multi-stage demolding to ensure the best printing effect. If the separation rate is too large, the viscosity of the solder paste will decrease, and the viscosity of the pad will also be small, which will cause part of the solder paste to adhere to the bottom surface of the stencil and the wall of the opening, resulting in printing quality problems, such as reduced printing volume and printing collapse. If the separation speed slows down, the viscosity of the solder paste will be large, and the solder paste will easily detach from the stencil.

 

 

7. Cleaner production mode and cleaning frequency

Stencil bottom washing is a factor to ensure the printing quality. The cleaning method and frequency should be determined according to the material of the solder paste, the thickness of the stencil and the size of the opening. If it is not cleaned in time, it will contaminate the surface of the PCB, and the residual solder paste around the openings of the stencil will harden, and in severe cases, the openings of the stencil will be blocked.

 

HOYOGO is an international, professional and reliable PCB Manufacturer. We not only have our own SMT factory, but also have many years of SMT processing experience, which can produce high-quality and high-efficiency products. We can provide SMT processing services for the Smallest package 0201 components, and supports various processing forms such as accepts customers' materials for processing and OEM.