How to Ensure the Fluidity of Solder Paste

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Solder-paste flowability is determined by viscosity and thixotropic index. To keep it flowing well, first store and warm it back per the procedures so the paste does not degrade or dry out. Stir it thoroughly before use so the powder and flux mix evenly and viscosity stabilizes. Hold the workshop at 23±3℃: if it is too cold, the paste thickens and flows poorly. Do not thin it with solvent on your own, as this destroys the flux system. Choose a paste whose viscosity matches the stencil and set the printing parameters accordingly, and the paste will print with good flowability and stable definition.

Solder Paste fluidity is a critical aspect of the SMT process that directly determines printing quality and subsequent soldering reliability. Selecting the appropriate solder paste type and strictly controlling its storage environment are fundamental requirements. It is generally recommended to store it between 5-30 degrees Celsius to avoid viscosity abnormalities caused by high or low temperatures.

In actual production, solder paste fluidity is affected by various factors, such as Flux Content, particle size, and distribution. High-activity Flux reduces viscosity but may increase corrosion risk, while coarse-particle solder paste tends to cause uneven printing. Therefore, matching must be performed according to specific process requirements.

After opening, solder paste must be thoroughly stirred to eliminate stratification; otherwise, metal particle sedimentation will occur, affecting the filling effect after printing. Meanwhile, ensure timely sealing after each use to prevent oxidation and moisture intrusion. These details all have a profound impact on fluidity.

During the printing process, the squeegee angle and pressure must also be precisely adjusted. An excessively small angle will cause excessive solder paste residue, while excessive pressure may over-squeeze the solder paste, thereby damaging its internal structure and ultimately affecting fluidity. Therefore, optimization must be combined with equipment parameters and product characteristics.

The standing time of solder paste after printing is equally important. Too short a time may result in incomplete spreading of the solder paste, while too long a time may cause viscosity increase due to volatilization, affecting wettability during subsequent Reflow Soldering. Therefore, a reasonable standing duration must be set according to the solder paste type and workshop environment.

For high-density or fine-pitch components, it is recommended to use low-viscosity solder paste with a precision printer. Meanwhile, regularly inspect squeegee wear to ensure a flat and burr-free printing surface. These measures can effectively improve the fluidity of the solder paste and reduce defect rates.

Finally, solder paste fluidity is not static but fluctuates with usage frequency and environmental changes. Therefore, a comprehensive management process must be established, including batch tracking, expiration date monitoring, and on-site testing, to continuously optimize process parameters through real-time data feedback.