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In SMT solder paste printing on PCB boards, one of the processes is to use a squeegee to squeeze the solder paste on the solder paste to transfer the solder paste from the stencil to the PCB board. The following PCBA processing process operators will introduce to you what are the advantages of the printing squeegee system.
The squeegee system is the most complex movement mechanism on the printing machine, including the squeegee fixing mechanism, the squeegee transmission control system, etc.
The function of the squeegee system is to expand the solder paste into a uniform layer on the entire template area. The squeegee presses the template to make the template contact with the PCB; the squeegee pushes the solder paste on the template to roll forward, and at the same time makes the solder paste fill the template opening; When the template is separated from the PCB, a proper thickness of solder paste is left on the PCB corresponding to the pattern of the template. The scrapers include metal scrapers and rubber scrapers, etc., which are used in different occasions. It must have high friction resistance and solvent cleaning performance,
and its hardness is an important factor affecting the quality of solder paste printing. The secondary knife made of rubber, when the pressure of the squeegee head is too large or the material is soft, it is easy to be embedded in the hole of the metal template (especially the large window hole), and the solder paste in the hole is squeezed out, thereby causing the printed pattern to dent, The printing effect is poor. For this reason, people use metal scrapers instead of rubber auxiliary knives. The metal auxiliary knife is made of high-hardness alloy, which is very resistant to fatigue, wear and bending, and is coated with a lubricating film on the blade. When the cutting edge runs on the template, the solder paste can be easily pushed into the window, eliminating solder pits and undulations.
In addition, a new type of closed scraper technology has emerged in recent years. Compared with the open scraper described above, it has the following advantages.
SMT airtight scraper
(1) Printing can still be performed even when the amount of solder paste is very small.
(2) It is beneficial to solder paste and can prevent the oxidation of solder paste.
(3) The effective utilization rate of solder paste is high.
(4) The internal pressure increases the solder paste filling effect, which can prevent the occurrence of poor printing.
(5) The process modulation is simpler and the printing speed is faster.
In the SMT processing industry, what does the red glue patch process mean?
There are two SMT red glue chip processing techniques. One is to dispense SMT red glue through a needle tube. According to the size of the component, the amount of SMT red glue is different. Manually dispense the SMT red glue machine. Time to control the amount of glue, the automatic dispensing SMT red glue machine controls the dispensing of the SMT red glue machine through different dispensing nozzles and dispensing time; the other is brushing glue, printing SMT red glue through the SMT patch stencil, SMT There are standard specifications for the size of the openings of the steel mesh.
SMT red glue patch processing is generally used for the process of power board, because the products processed by SMT patch red glue process require SMD patch components to be above 0603 in order to be mass-produced.
At present, there is another process in the SMT chip processing industry, called dual process. That is, the SMT patch red glue process and the solder paste process are carried out at the same time. After printing the solder paste, red glue is applied. Or open the SMT ladder steel mesh and print the red glue again. This process is used in the production of PCBA boards that require tin penetration but with more SMD components. At present, this process is very mature.
The main defects produced by SMT red glue patch processing are: PCB pad overflow, SMD component floating, SMT red glue insufficient adhesion, SMD component bumping, etc.; the pre-process includes red glue storage, warming before use, and printing The rear PCB board should be placed flat, and the storage time after printing should not be too long. The temperature of the reflow oven is generally above 130 degrees for 90 to 120 seconds, and the maximum temperature does not exceed 150 degrees. The specific requirements depend on the reference requirements given by the red glue used. ;
