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The example in Figure 1 is fairly unusual, but is an excellent example of paste particle bleed due to printer board vacuum on the printer. Basically, during printing some engineers use a vacuum to hold boards flat. When the stencil is sitting on the surface of the board, any gap can be a path for paste bleed. The paste is literally sucked off the surface of the pad.

Figure 1: During vacuum hold-down, a gap caused this bleed.

Normally, if this is a bleed issue, the same type of fault will be seen on repeated boards, but be careful during assessment--under stencil paste contamination can produce the same type of defect.

Damaged Stencils	Stencil Blockage	Paste Misalignment	Smudged Paste	Poor Definition
Incomplete Prints	Residues	Bleeds	Ears	Scooping
Shorts	Slump	PIHR Printing