PCB News - How to remove the solder paste misprinted on the PCB board

How to remove the solder paste misprinted on the PCB board

Solder paste In printing, low-viscosity solder paste may also cause printing defects. The viscosity should be moderate, the operating temperature of the printing machine is high or the squeegee speed is high, which can reduce the viscosity of the solder paste in use. If too much solder paste is deposited, it will cause printing defects and bridging in the PCB chip processing. For high-density pitch stencils, if the thin stencil cross-section bending causes damage between the pins, it will cause solder paste to deposit between the pins and cause printing defects. The circuit boards with printing defects in the solder paste printer should remove the misprinted solder paste. Next, the editor of the circuit board factory will introduce how to remove the excess solder paste that was misprinted on the PCB board.

Using a small spatula to remove the solder paste from the misprinted PCB may cause some problems. It is generally feasible to immerse the misprinted board in a compatible solvent, such as water with some additives, and then use a soft brush to remove the small tin beads from the board. I would rather soak and scrub repeatedly than violently dry brushing or shoveling. After the solder paste is printed, the longer the operator waits to clean the misprint, the more difficult it is to remove the solder paste. Misprinted boards should be placed in the soaking solvent immediately after the problem is discovered, because the solder paste is easy to remove before it dries.

Avoid rubbing with cloth strips to prevent solder paste and other contaminants from smearing on the surface of the board. After soaking, scouring with a gentle spray can often help remove unwanted tin drafts. It is also recommended to use hot air for drying. If a horizontal stencil cleaner is used, the side to be cleaned should face down to allow the solder paste to fall off the board.

As usual, paying attention to some details can eliminate undesirable situations, such as misprinting of solder paste and removal of solidified solder paste from the board. It is our goal to deposit an appropriate amount of solder paste at the desired location. Dirty tools, dried solder paste, and misalignment of the template with the PCB board may cause undesirable solder paste on the bottom surface of the template or even the assembly. During the printing process, the template is wiped according to a certain rule between printing cycles. Ensure that the template is located on the pad, not on the solder mask, to ensure a clean solder paste printing process on the PCB. Online, real-time solder paste inspection and inspection before reflow after component placement are all process steps that help reduce process defects before soldering occurs.

For fine-pitch templates, if the thin template cross-section bending causes damage between the pins, it will 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, the high operating temperature of the printer or the high squeegee speed can reduce the viscosity of the solder paste in use, and cause printing defects and bridging due to the deposition of too much solder paste.

In general, lack of adequate control over materials, solder paste deposition methods and equipment are the main causes of defects in the reflow soldering process.

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