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Stencil, Solder Paste & Printing Defects - Damaged
Stencils
Because a stencil may cost between $300 - 600, care needs
to be taken on handling and printer set-up. If kinks or buckles in the stencil
occur as shown in these examples, the stencil will not sit flat on the surface
of the printed circuit board resulting in poor print characteristics.
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| Figure 1: A stencil buckle on the edge of a BGA pad
area. |
Damage to the stencil can cause paste to seep around the BGA
aperture onto the surface of the laminate and resist. This may result in
paste shorts, which can lead to solder shorts. Damage like the example can
often occur due to excessive pressure of the squeegee blade or on the stencil
on contact force. The stencil is literally bent over the edge of PCB.
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| Figure 2: Another stencil buckle. |
More Stencil, Solder Paste & Printing Defects:
Damaged Stencils | | | | |
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© 2007 Trafalgar Publications
Text and photos courtesy of Bob Willis |
