How solder paste affects the printing quality?
In SMT processing, solder paste printing is a very important and complex process; the authoritative statistics of the electronics industry show that in the SMT manufacturing process, solder paste printing results have a significant impact on?SMT?manufacturing quality; affecting solder paste printing There are many factors of quality, such as the manufacturing process of stencil, the angle and material of the squeegee, the opening design of the stencil, the flatness of the PCB, the setting of the printing parameters, the characteristics of the solder paste itself, etc.
Today we are talking about how solder paste affects printing quality and how to control solder paste.
The characteristics of the solder paste itself, the specific gravity of the metal content, the viscosity of the solder paste, the size of the metal particles, and the thixotropic properties of the solder paste may affect the printing quality.
Change in solder paste viscosity due to temperature
Solder paste has the property of changing viscosity due to changes in ambient temperature.
In the case of continuous use, the low-viscosity solder paste may cause defects such as solder paste collapse and penetration, and defects such as solder paste deformation during mounting of the parts, and are also an important factor in the occurrence of solder balls and bridge short-circuits.?
In addition, the high-viscosity solder paste tends to cause squeegee such as poor soldering and insufficient printing during use, and therefore it is necessary to set the corresponding solder paste viscosity in combination with the use environment.?
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Solder paste control in SHC
2. Solder paste should be stored at 2-10 ° C, used on a first-in, first-out basis, and controlled by a regulatory label. The solder paste is not unsealed at room temperature and the temporary storage time shall not exceed 48 hours. If it is not used, put it back in the refrigerator for refrigerating. The opened solder paste should be used within 24 hours. If it is not used, please put it back into the refrigerator and store it in time.
3. The automatic solder paste printing machine requires that the solder paste on both sides of the scraper be gathered every 20 minutes, and the new solder paste is added once every 2-4H.
4. The first piece of solder paste printing takes 9 points to measure the thickness of solder paste. The thickness of tin is: upper limit, thickness of stencil + thickness of stencil * 40%, lower limit, thickness of stencil + thickness of stencil * 20%. If the fixture is used for printing, the fixture number is indicated on the PCB and the corresponding fixture. It is convenient to confirm whether the fixture is defective due to abnormality; the reflow soldering furnace temperature data is transmitted back, and at least once a day is guaranteed. The tin thickness is controlled by SPI. It is required to measure once every 2H, the appearance inspection report after the furnace, 2H transmission once, and the measurement data is transmitted to our company's process;
5. Poor solder paste printing, use a clean cloth, wash the PCB surface solder paste, and use a wind gun to clean the residual tin powder on the surface;
6. Before the self-checking solder paste, there is no bias or tin tip. If the printing is bad, it is necessary to analyze the abnormal cause in time. After adjusting, focus on checking the abnormal problem.