As usual, paying attention to some details can eliminate defects, such as solder paste printing errors and removing solidified solder paste from the board. Our goal is to deposit an appropriate amount of solder paste at the desired location. Dirty tools, dried solder paste, and misalignment between templates and boards can all result in residual solder paste on the bottom surface of the template or even during assembly. During the printing process, wipe the template according to a certain pattern between printing cycles. Ensure that the template is located on the solder pad, not on the solder mask, to ensure a clean solder paste printing process. Online, real-time solder paste inspection and inspection before reflow after component placement are both helpful process steps in reducing process defects before soldering occurs. For fine pitch templates, if the thin cross-section of the template bends and causes damage between the pins, it can cause solder paste to deposit between the pins, resulting in printing defects and/or short circuits. Low viscosity solder paste may also cause printing defects. For example, high operating temperatures or blade speeds of printing machines can reduce the stickiness of solder paste during use, causing printing defects and bridging due to excessive deposition of solder paste. Overall, the lack of sufficient control over materials, methods and equipment for solder paste deposition are the main reasons for defects in reflow soldering processes.

Using a small scraper to remove solder paste from the misprinted board may cause some problems. The generally feasible method is to immerse the misprinted board in a compatible solvent, such as water with a certain additive, and then use a soft bristled brush to remove the small tin beads from the board. I would rather soak and wash repeatedly than vigorously dry brush or scrape. After solder paste printing, the longer the operator waits to clean the misprints, the more difficult it is to remove the solder paste. The wrongly printed board should be immediately immersed in a solvent after discovering the problem, as the solder paste is easy to remove before it dries.

Avoid using cloth strips to wipe and prevent solder paste and other contaminants from being applied to the surface of the board. After soaking, washing with a gentle spray can often help remove unwanted tin drafts. It is also recommended to use hot air drying. If a horizontal template cleaning machine is used, the surface to be cleaned should face downwards to allow the solder paste to fall off the board.