Squeegee Selection and Wear
What the Squeegee Does
The squeegee is the blade that rolls the paste across the stencil and presses it into the apertures. The deposit’s volume and its uniformity depend on how the blade behaves: how it deforms under pressure, how it meets the stencil’s surface and how it releases the paste as it passes. A squeezed blade that is too soft conforms to the apertures and scoops paste out of them, while one that is too hard does not conform and leaves paste on the surface. The squeegee is therefore a process component with an optimum, not a consumable chosen by availability.
Material and Hardness
The common materials are polyurethane and metal, and the hardness is quoted in a durometer scale. A softer blade conforms more and is used on an uneven surface, at the cost of scooping; a harder blade holds its edge and produces a cleaner wipe, and it is used where the board and the stencil are flat. Metal blades are used where the paste’s rheology needs a sharp edge, and their hardness makes the stencil’s wear a consideration. The hardness should be matched to the paste and the substrate, and the choice should be recorded with the print parameters since a change of blade changes the deposit.
Edge Condition
The edge is what does the work, and it is also what wears. A new blade has a sharp, square edge; after use it becomes rounded or nicked, and a nicked edge leaves a streak of paste on the stencil surface that is then dragged into the next aperture. The wear accelerates with a hard blade, a rough stencil and an abrasive paste. The edge should be inspected at magnification as part of maintenance, and a blade with a nick or a rounded edge should be replaced rather than used for a less critical product, because the defect it produces is intermittent and hard to attribute.
Pressure and Angle
The pressure decides how the blade meets the stencil. Too little pressure leaves a film of paste on the stencil surface and produces an inconsistent deposit; too much forces the blade into the aperture and scoops the paste out, and it also wears the blade and the stencil faster. The correct pressure is the minimum that produces a clean wipe, and it should be established by printing a test pattern and measuring the deposits rather than by feel. The angle of the blade relative to the stencil matters as well: a steeper angle presses the paste into the aperture more, and a shallower one wipes more. The two are related, so a change to one usually requires a change to the other.
Print Speed and Separation
The speed affects how the paste rolls and how much time the aperture has to fill. A speed that is too high can leave the aperture partially filled and can cause the paste to be thrown rather than rolled; one that is too low allows the paste to dry at the blade. The separation speed is the other half of the release: a fast separation pulls the paste from the aperture and leaves a ragged deposit, while a slow one allows the paste to release cleanly. Both parameters should be established together with the pressure, and the combination should be recorded as the product’s print recipe.
Maintenance and Records
The squeegee should be part of the printer’s maintenance schedule, with the blade’s edge inspected, the pressure verified and the angle checked. The blade should be stored so that its edge is not damaged, and it should be replaced on a schedule related to its use rather than when a defect appears. The records matter because the print recipe is only valid for the blade it was developed with: a change of material or hardness invalidates the settings, and a blade that has worn changes the effective pressure. Keeping a note of the blade’s identity with the print recipe makes the diagnosis of a print problem much faster.
Symptoms of a Squeegee Problem
The symptoms are recognisable. A streak of paste on the stencil surface that reappears in the same place follows a nick in the edge. A deposit that is thicker on one side of the board suggests an uneven blade or an uneven pressure. A deposit that becomes progressively thinner through a run suggests a blade that is deforming or a pressure that is decaying. Paste left on the stencil after the stroke suggests a pressure that is too low or a speed that is too high. Reading those symptoms as squeegee problems rather than as paste problems saves a great deal of time.
Blade Length and the Board’s Width
The blade has to span the print area, and a blade that is longer than necessary concentrates its force on the part of the stencil it spans and deflects elsewhere. Where the board is narrower than the printer’s maximum, a shorter blade reduces the total force required and improves the uniformity across the board. The blade’s length should therefore be matched to the product’s width, and a printer that runs several product sizes should have more than one blade. A blade that is too long is one of the reasons a deposit varies from the leading edge to the trailing edge of a panel.
FAQ
Which squeegee hardness is best? It depends on the paste and the flatness of the substrate; the pressure and angle are as important as the hardness.
Why does a nick in the blade matter? It leaves a streak of paste that is dragged into the next aperture, producing an intermittent defect.
How much pressure is correct? The minimum that produces a clean wipe, established by measuring deposits rather than by feel.
What does a fast separation cause? The paste is pulled from the aperture, leaving a ragged and incomplete deposit.
Why record the blade with the recipe? The settings are only valid for that blade, so a change of material or wear invalidates them.
Conclusion
The squeegee is a process component whose material, edge, pressure and angle decide the deposit, so set it deliberately, maintain it and record it with the recipe. Print control belongs to SMT PCB assembly, the paste it moves is described in PCB assembly, and the acceptance is part of quality management. Print recipes for a new product are developed during prototype PCB assembly in 2026.
