During the PCB stencil manufacturing process, the continuous action of the laser beam can cause the openings or aperture walls to become rough. This occurs because the laser melts the sheet material, resulting in surface abnormalities such as micro-burrs on the aperture walls. To address this issue, the electropolishing process is used to smooth the aperture walls, facilitating the smooth transfer of solder paste from the stencil to the target PCB pads.

Principle of Electropolishing for PCB Stencils

The electropolishing process for stencils is an electrolytic process, where the electropolishing tank functions as an electrolytic cell. The stencil is fixed to the anode and immersed in the electropolishing solution, with a high current passed through it. During this process, a viscous, high-resistance film forms on the surface of the stencil. This film is thinner on the microscopic protruding areas and thicker in the microscopic recessed areas. As a result, the current density distribution is uneven. The current's edge effect causes the protruding areas to have a higher current density, leading to rapid dissolution, while the recessed areas have a lower current density, causing slower dissolution. This differential dissolution reduces the size of the protruding areas more quickly than the recessed areas, achieving a smooth and leveled surface.

Advantages of Electropolishing PCB Stencils

Laser-cut stencils use the concentrated energy of a laser beam to melt stainless steel material and create openings. During this process, metal slag can form along the edges of the aperture, and the aperture walls are often rough, which can affect the accuracy of solder paste printing and, consequently, the soldering process. To address this issue, electropolishing has been introduced as an improvement measure. The advantages of electropolishing are as follows:

 1. Improved Cleanliness: Electropolishing significantly enhances the cleanliness of the stencil by removing surface impurities.

 2. Better Flatness: Electropolishing smooths the surface of the stencil, removing or reducing existing stress layers and preventing the formation of additional stresses.

 3. No Metallurgical Layer: Electropolishing does not create a metallurgical layer on the surface, preserving the material properties of the stencil.

 4. Applicable to Various Materials: Electropolishing is suitable for hard, soft, thin-walled, complex-shaped, or small components that are difficult to polish mechanically.

 5. Reduced Friction, Improved Solder Paste Release: Electropolishing reduces the surface friction of the aperture walls, which helps improve the solder paste release and reduces the occurrence of voids.

 6. Efficient Production: Electropolishing is a quick process and can handle multiple stencils simultaneously, improving production efficiency.

 7. Enhanced Soldering Performance: Electropolishing removes or improves the slag and burrs in the laser-cut stencil aperture walls, thereby effectively improving the stencil's ability to release solder paste.