How to Prevent Solder Paste Drying During SMT Printing Process

In the SMT (Surface Mount Technology) production process, solder paste drying is a persistent pain point that plagues electronic manufacturers worldwide. Once solder paste dries prematurely or loses fluidity, it directly leads to printing defects such as insufficient solder, bridging, tin balls, and poor wetting, which in turn reduce production yield, increase material waste and rework costs, and even disrupt the entire production schedule. The root cause of solder paste drying is not only related to environmental factors but also closely linked to the stability of printing equipment and process parameters. This article will deeply analyze the core causes of solder paste drying and provide systematic solutions, focusing on how to rely on precision testing equipment to eliminate potential risks from the source.
Core Causes of Solder Paste Drying in SMT Printing
Solder paste is a non-Newtonian fluid composed of solder powder, flux, and additives. Its fluidity and stability are highly sensitive to external conditions. The main factors leading to drying during the printing process can be summarized into the following categories:
1. Uncontrolled Environmental Temperature and Humidity
Most solder pastes require an operating environment with a temperature of 20-25℃ and a relative humidity of 30%-60% <superscript:7. When the ambient temperature exceeds 25℃, the solvent in the flux volatilizes rapidly, and the chemical reaction rate between the flux and solder powder doubles for every 10℃ increase in temperature <superscript:7. Low humidity (below 30%) will further accelerate the loss of volatile components in the solder paste, causing it to harden on the stencil surface. Fluctuations in temperature and humidity during multi-shift production will also make the solder paste in a cycle of "drying-softening", damaging its internal structure and leading to uneven flux distribution <superscript:4.
2. Improper Squeegee Parameters and Wear
Squeegee pressure, angle, and speed are core parameters affecting solder paste state. Excessive pressure (exceeding 0.5MPa) will cause repeated friction between the solder paste and the stencil, generating shear heat and accelerating solvent volatilization <superscript:3. Insufficient pressure, on the other hand, leads to solder paste residue on the stencil, which dries and cakes after long-term exposure to air <superscript:10. Squeegee wear, edge defects, and poor straightness will cause uneven pressure distribution during printing. The worn part will squeeze the solder paste excessively, while the intact part cannot fully fill the stencil openings, resulting in local drying and printing defects <superscript:2.
3. Lack of Real-Time Monitoring and Process Traceability
Traditional manual inspection of squeegee status is subjective and inefficient, making it impossible to detect micro-wear (less than 0.01mm) and edge defects in a timely manner. When obvious drying defects appear, a large number of products have already been scrapped. In addition, the lack of systematic data recording of squeegee usage and detection results makes it difficult to trace the root cause of solder paste drying, and it is impossible to optimize parameters based on historical data <superscript:5.
Systematic Solutions to Prevent Solder Paste Drying
To fundamentally solve the problem of solder paste drying, it is necessary to combine environmental control, process optimization, and precision equipment monitoring, among which the stable operation of the squeegee is the key link to reduce unnecessary solder paste loss.
1. Standardize Environmental Control Management
Equip the production workshop with intelligent temperature and humidity control systems to maintain a constant environment within the range of 20-25℃ and 30%-60% relative humidity. Avoid placing the solder paste near heating equipment or air vents, and strictly follow the operation specifications: take the refrigerated solder paste out for 2-4 hours of rewarming before use to prevent moisture condensation caused by temperature difference from entering the paste <superscript:8. After use, seal the solder paste immediately to reduce exposure time to air.
2. Optimize Squeegee Process Parameters
According to the IPC7525 standard, adjust the squeegee parameters dynamically based on stencil thickness and opening size <superscript:3. The optimal pressure range is 0.2-0.5MPa, and the angle is controlled between 45°-60°, among which 55° is suitable for most component printing scenarios, as it can promote shear thinning of the solder paste and reduce friction heat <superscript:3. Match the printing speed with the squeegee angle: when the speed exceeds 50mm/s, appropriately increase the angle to 58° to compensate for shear force loss <superscript:3. Avoid excessive pressure adjustment and reduce repeated scraping of the solder paste.
3. Rely on Precision Detection Equipment to Ensure Squeegee Stability
The stability of the squeegee directly determines the state of the solder paste during printing. Automatic squeegee inspection equipment can effectively eliminate hidden dangers caused by squeegee defects and parameter deviations, and build a solid barrier for preventing solder paste drying.
Equipped with high-definition industrial cameras (above 12 million pixels) and high-brightness LED backlight sources, the equipment can accurately detect the straightness, edge wear, and surface defects of the squeegee with a detection accuracy of ±0.01mm <superscript:5. The 000-grade marble platform ensures stable detection results and avoids measurement errors caused by equipment vibration. Through intelligent image processing algorithms, the system automatically compares the detected data with standard parameters, quickly judges whether the squeegee is qualified, and timely alarms for worn or deformed squeegees to prevent them from entering the production line and causing solder paste drying.
In terms of parameter control, the equipment can automatically monitor and adjust the squeegee pressure to ensure that it is always within the optimal range of 0.2-0.5MPa, avoiding excessive friction heat caused by pressure deviation<superscript:5. At the same time, it is equipped with a code scanning function to quickly enter the squeegee code, realize full-process data traceability, and store detection results, usage time, and parameter adjustments in the system. By docking with the MES system, it can realize intelligent management of production data, help engineers analyze the correlation between squeegee status and solder paste drying, and provide data support for process optimization<superscript:5.
Conclusion
Preventing solder paste drying during SMT printing is a systematic project that requires the integration of environmental control, process optimization, and equipment monitoring. Among them, the stable operation of the squeegee is the core to reducing solder paste friction and solvent volatilization. Automatic squeegee inspection equipment, with its high-precision detection capability, intelligent parameter control, and full-process data traceability, can fundamentally solve the pain points of untimely detection of squeegee defects and unstable parameters, effectively extending the service life of solder paste, improving printing yield, and reducing production costs for manufacturers. In the context of increasingly miniaturized and high-precision electronic products, relying on such precision equipment to optimize the SMT printing process has become an inevitable trend for enterprises to improve core competitiveness.