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What factors affect the quality of SMT laser stencil?

What factors affect the quality of SMT laser stencil?

 SMT laser stencil
About Stencils:
 
Stencils (SMT stencil): it is a special SMT mold; its main function is to help solder paste deposition; the purpose is to transfer accurate amount of solder paste to the exact position on PCB.

Stencils classification
 
According to the manufacturing process of SMT stencil, it can be divided into: laser stencil, electropolishing stencil, electroforming stencil, step steincil, bonding stencil, nickel plated stencil, etching stencil. Laserstencil is the most commonly used stencil in SMT stencil industry. Its characteristics are: directly using data files to produce, reducing the production error link; SMT stencil opening position precision is extremely high: the whole process error is less than ± 4 μ m; the opening of SMT stencil has geometric figure, which is conducive to the printing and forming of tin paste.

Manufacturing technology
 
The manufacturing process of Stencil includes chemical etch, laser cutting and electroform.

The following factors will affect the quality of PCB stencil:
 
1. Production process: we have discussed the production process of stencil in front of us. We can know that the best process should be electropolishing after laser cutting.
 
2. Materials used: including PCB frame, wire mesh, steel sheet, adhesive, etc. PCB mesh frame must be able to withstand the relay of a certain program and have good levelness; polyester mesh is better used for wire mesh, which can maintain stable tension for a long time; steel sheet is better to use 304, and the matte will be more conducive to the solder paste (glue) rolling than the mirror; the adhesive must be strong enough and resistant to certain corrosion.
 
3. Opening design: the quality of opening design has the greatest impact on the quality of PCB steel mesh. As discussed above, the opening design should consider the manufacturing process, width thickness ratio, area ratio, experience value, etc.
 
4. Production data: the integrity of production data will also affect the quality of PCB stencil. The more complete the information, the better. At the same time, when the data coexist, it should be clear which is the most important. In addition, generally speaking, the error can be reduced as much as possible by using data files to make stencil.
 
5. How to use: correct printing method can keep the quality of stencil. On the contrary, incorrect printing method, such as excessive pressure, PCB stencil or PCB not level, will damage stencil.
 
6. Cleaning paste (glue) is easy to solidify. If it is not cleaned in time, it will block the opening of stencil, and it will be difficult to print next time. Therefore, after PCB stencil is removed from the machine or printed on the printer for 1 hour, the solder paste should be cleaned in time.
 
7. The storage of stencil should be in a specific storage place and should not be placed randomly, so as to avoid accidental injury to tencil. At the same time, PCB stencil should not be stacked together, which is not easy to take and may bend the mesh frame.

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