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How SMT prints solder paste on PCB circuit board
PCBA Tech
How SMT prints solder paste on PCB circuit board

How SMT prints solder paste on PCB circuit board

2021-11-10
View:37
Author:Downs

Everyone knows that everyday electronic products have a PCB circuit board inside, which is densely covered with various electronic components, and how are these electronic components mounted on the PCB board?

The editor below will introduce to you how the SMT front-end equipment solder paste printer prints the solder paste onto the circuit board, so that the electronic components can be better mounted and soldered.

Everyone is familiar with PCB circuit boards. There are many pads (PAD) on the PCB. In the smt chip processing process, in order to make the solder paste cover the specific pads, it is necessary to make a piece corresponding to the position of the pad. The steel plate is installed on the solder paste printer to ensure that the steel plate mesh is at the same position as the pad on the PCB. After the positioning is completed, the squeegee on the solder paste printer is moved back and forth on the stencil, and the solder paste penetrates the mesh on the steel plate to cover Finish the solder paste printing on the specific pads of the PCB.

pcb board

Further reading:

What are the types of solder paste in SMT chip processing, and the basic understanding of storage and use environment

SMT solder paste printer classification

1. Fully automatic solder paste printing machine: The smt production line of general large-volume/mainstream placement machine is a full-automatic printing machine production line. As long as the relevant parameters of the printing machine are set, the machine can automatically feed the plate and the steel plate automatically Position, print solder paste, output the board, and automatically transfer to the next workstation through the conveyor belt.

2. Semi-automatic solder paste printing machine: The semi-automatic solder paste printing process mostly occurs in the trial production stage or a small number of diverse product lines. The board loading, unloading, and steel plate alignment are usually operated manually, and only the solder paste printing is automatically operated. You must be a master to operate this type of equipment, otherwise it is easy to produce bad boards. Choosing this type of semi-automatic printing machine does not want to occupy the entire SMT automatic production line on the one hand, and the semi-automatic solder paste printing machine is relatively cheaper.

3. Manual solder paste printer: This is usually in areas where low-priced products and low labor costs. There are basically no manual printers in mainland China. All are manually operated. Only steel plates, squeegees and solder paste can be completed. .

Standards for judging the quality of solder paste printing

1. The position of solder paste printing

2. Printing volume of solder paste

The above two types are the standards for testing the printing quality of the solder paste printer. If the solder paste printing is not good, it will often cause the PCB to have less tin, more tin and sticky tin. The occurrence of these types will often cause short-circuit and empty soldering problems in the solder.

Factors affecting the quality of solder paste printing

1. Type of squeegee: For solder paste printing, choose the appropriate squeegee according to the characteristics of the unused solder paste or red glue. At present, most of the mainstream squeegees are made of stainless steel.

2. Scraper angle: The angle at which the squeegee scrapes the solder paste, generally between 45-60 degrees.

3. Squeegee pressure: The pressure of the squeegee affects the amount of solder paste. The greater the pressure of the squeegee, the less the amount of solder paste. Because of the high pressure, the gap between the steel plate and the circuit board is compressed.

4. Squeegee speed: The speed of the squeegee affects the shape and amount of solder paste printing, and also directly affects the quality of the solder. Generally, the squeegee speed is set between 20-80mm/s. In principle, the speed of the squeegee must match the solder paste. The higher the viscosity, the better the flowability of the solder paste, the faster the scraper speed should be, otherwise it is easy to seep.

5. Stripping speed of steel plate: too fast stripping speed can easily cause the phenomenon of solder paste drawing or sharpening

Whether to use a vacuum seat: The vacuum seat can help the circuit board to be smoothly attached to a fixed position and strengthen the tightness of the steel plate and the pcb circuit board.

6. Whether the circuit board is deformed: The deformed circuit board will cause the solder paste to be printed unevenly, and in most cases it will cause a short circuit.

7. Steel plate opening: the steel plate opening directly impresses the solder paste printing quality

8. Steel plate cleaning: Whether the steel plate is clean is related to the quality of solder paste printing, especially the contact surface of the steel plate and the PCB circuit board, to avoid the residual solder paste on the steel plate from getting to the position on the PCB where there should be no solder paste. Generally, the smt chip factory is in After producing a few pieces of boards, use test paper to clean the bottom of the steel plate. Some printers are designed with automatic wiping function. It is also necessary to specify how often the steel plate should be removed with a solvent for cleaning. The purpose is to remove the residual solder paste from the steel plate opening, especially the small ones. Pitch PCB pads to ensure that the solder paste printing is not blocked.