Solder paste generally accumulates on the underside of the stencil because small amounts of paste ‘bleed’ throughout the imperfect seal between stencil and board. This phenomenon is made worse by misalignment, by squeegee pressures outside the process window, and by poor release of paste from the stencil.
If the underside of the stencil is not regularly cleaned, this can result in smeared prints and an increased likelihood of solder shorts and solder balling.
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