Maintenance Operation
Clearing of residual solder paste from the underside of a printing foil is essential for maintaining deposition accuracy over long runs. This process, known as under stencil wiping, employs a moving paper roll and vacuum to clean the bottom surface of the stencil.
Defect Prevention
Solder paste that squeezes out of the apertures can accumulate on the bottom of the foil. If this material is not removed, it transfers to subsequent boards, creating solder balls and bridges between adjacent pads. Automated wiping cycles are programmed into the printer to run after a set number of print strokes.
This automated cleaning prevents paste build up and keeps output defect rates low without manual operator intervention.
Fluid Selection
Solvent choice during the wipe sequence determines the effectiveness of the paste removal. Using a fast evaporating solvent prevents wet residue from diluting the solder paste in the next print stroke. Dry wipes can be combined with wet and vacuum steps to ensure that the stencil apertures remain open and clean.
If the solvent is too aggressive, it may attack the stencil tensioning adhesive or cause polymer nano coatings on the foil to degrade. Optimal clean parameters must be established for each paste type to balance cleaning efficiency with stencil lifespan.
