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What are the causes of insufficient and uneven solder paste in SMT steel mesh, and what solutions are available?

Source: Lin Chuan precision article author: Lin Chuan precision time: 2020-02-25 12:10 reading: 1432

SMT steel mesh is a kind of mold specially used for printed circuit board. SMT steel mesh mounting technology refers to the surface assembly technology of circuit assembly, that is, surface assembly components without pins or short leads are installed on the surface of printed circuit board or other substrates, and then welded and assembled by reflow soldering or immersion welding. Insufficient and uneven solder paste often occurs in SMT production. The following is to share with you the specific reasons for this problem and solutions.

 Paste effect of SMT stencil printing
Paste effect of SMT stencil printing

   What are the reasons for insufficient and uneven solder paste in SMT steel mesh patches

  1. The fixing clamp of circuit board in SMT stencil printing machine is loose.

2. Solder spatula or SMT steel mesh is damaged.

3. When SMT stencil printing machine works, it can not make up for the increase of solder paste in time.

4. The unused solder paste has expired and has been reused.

5. The thickness of SMT steel mesh is not uniform.

6. Quality problem of circuit board. There is an inconspicuous covering on the pad, such as a solder mask (green oil) printed on the pad.

7. The pressure, angle, speed, demoulding speed and other equipment parameters of the printing scraper are not set correctly.

 Relationship between pressure, speed and angle in SMT stencil printing

Relationship between pressure, speed and angle in SMT stencil printing

8. There are coarse and hard impurities in SMT steel mesh or tin welding.

What are the solutions for uneven solder paste in SMT stencil circuit printing

   1. Some mesh walls of SMT steel mesh are not smooth. Electropolishing is recommended.

2. The SMT steel mesh must be cleaned after use, and there must be no residual solder paste or other impurities. It is recommended to use automatic SMT steel mesh cleaning.

 Automatic SMT steel mesh cleaning machine

Automatic SMT steel mesh cleaning machine

In addition, the following other factors need to be considered:

1. Solder paste is dry or too sticky. You can try using more solder paste.

2. Scraper pressure and demoulding speed during printing.

3. If it is an automatic printing machine, it should consider whether the amount of alcohol sprayed is too large and whether the steel mesh paper after cleaning is wet. Is it more difficult to tin every time the mesh is cleaned?

Thank you for the above analysis of the reasons why the SMT paste is not uniform. If you need more relevant content, you can contact online customer service, or call 18928403435 to send the file content to Luohua @ lcjmi.com, and we will provide you with more services.


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