After cleaning SMT solder paste stencils with aqueous cleaning fluid, rapid drying is crucial for ensuring cleaning quality and subsequent production efficiency. Aqueous cleaning fluids are widely used due to their environmental friendliness and compatibility with stencil materials. However, if residual moisture is not completely removed after cleaning, it can cause rusting, secondary contamination with solder paste residue, and compromise printing accuracy. Therefore, a multi-stage drying strategy should be implemented, taking into account the structural characteristics of the stencil and the cleaning process requirements, to balance drying efficiency and safety.
After cleaning with aqueous cleaning fluid, a large amount of moisture will adhere to the stencil surface. This moisture may seep into the stencil openings or accumulate at the bottom of the stencil, creating hidden damp areas. Directly drying in air not only takes a long time but can also cause localized moisture re-entry due to ambient humidity. Therefore, drying should be initiated immediately after cleaning, prioritizing physical removal of most surface moisture. For example, compressed air can be used to purge along the stencil openings, using air pressure to squeeze moisture out of the holes while avoiding direct airflow that could cause solder paste residue to splash. Maintain a uniform airflow during purge to prevent excessive localized pressure that could damage the stencil tension.
For stubborn moisture remaining on the stencil surface, hot air circulation drying can be used. Hot air drying accelerates moisture evaporation through high-temperature airflow while preventing deformation of the stencil due to local overheating. In practice, the stencil should be suspended in dedicated drying equipment, with the hot air temperature set between 40-60°C to ensure rapid moisture evaporation without exceeding the stencil's heat resistance. During the drying process, the equipment's circulating fan should operate continuously to ensure even coverage of the hot air across all areas of the stencil, particularly at the bottom of the stencil and areas with dense openings to prevent incomplete drying due to dead air pockets.
If the stencil has small openings or a complex structure, hot air drying may not completely remove moisture from the pores. In this case, centrifugal drying can be combined with this technology. Centrifugal drying uses high-speed rotation to generate centrifugal force, removing moisture from the stencil's surface. It is particularly suitable for removing residual moisture from tiny openings. The stencil should be secured to the centrifugal dryer's turntable and set to a speed between 800-1200 rpm. This ensures that the centrifugal force is sufficient to overcome the surface tension of the water, while avoiding excessive speed that could cause the stencil to shift or damage. The centrifugal drying time is typically controlled within 3-5 minutes. The stencil should be removed immediately after drying to prevent local overheating due to residual heat from the equipment.
For stencils requiring high precision, a secondary inspection and treatment is required after drying. Use a magnifying glass or microscope to inspect the stencil openings for cleanliness and dryness. If residual moisture or water stains are detected, wipe the area with a dust-free cloth dipped in a small amount of isopropyl alcohol (IPA). IPA is highly volatile and highly soluble, quickly removing residual moisture and preventing oxidation. However, the amount used should be controlled to prevent IPA from seeping into the stencil and affecting subsequent use. After wiping, blow the stencil again with compressed air to ensure it is completely dry.
The dried stencil should be stored in a dry, dust-free environment, avoiding contact with moisture or corrosive substances. A dedicated stencil rack can be used for storage, and the stencil should be hung horizontally to prevent deformation due to gravity. A dust cover should also be placed on the stencil surface to reduce dust adhesion and extend its life. If the stencil needs to be stored for an extended period, it is recommended to regularly check its dryness and re-dry it if necessary to ensure it is always in optimal condition.
In actual production, drying difficulties can also be reduced by optimizing the cleaning process. For example, adding an appropriate amount of defoaming agent to the aqueous cleaning fluid can reduce the amount of foam generated during the cleaning process and minimize water retention caused by residual foam. Alternatively, a staged rinsing technique can be employed, using a low-concentration cleaning solution for an initial rinse followed by a final rinse with deionized water to reduce residual salt on the stencil surface and thus shorten drying time. These process optimization measures can synergize with drying technology to further improve stencil cleaning efficiency and quality.
