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Stencil, Solder Paste & Printing Defects - Solder Paste Shorts Solder paste shorts can occur on the surface of the board between pads. This type of defect can result in solder shorts, solder balls or variations in the volume of joints after reflow. Paste shorts or bleeding can occur when the stencil is not fully in contact with the pad surface. Excessive squeegee pressure or a combination of speed and high pressure can also cause this problem.
Variations on the surface of the board, like thick solder mask, uneven pad coatings or masking on the board may lift the stencil off the surface of the PCB, causing paste seeping. PCB identification labels or barcode labels close to the print area can also affect on printing quality.
When setting up a stencil, the stencil and the board should be intimate contact with minimum pressure. Excessive squeegee pressure or a combination of speed and high pressure can also cause this problem.
More Stencil, Solder Paste & Printing Defects:
Text and photos courtesy of Bob Willis |
