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The image of this 0.020" pitch print in Figure 1 shows an uneven print with paste ears at each end of the paste deposits.

Figure 1: Solder paste ears shown at each end of the paste deposits.

This phenomenon occurs when the paste does not separate cleanly from the stencil. This can be related to the paste, the stencil or the aperture size and stencil thickness. Trying to print small pitches with a thick stencil will always result in paste sticking in the aperture, particularly at the ends.

If printing parts like this are necessary, then reduce the length of the aperture rather than the width for better release of the paste.

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