Squeegee Selection and Print Quality
The squeegee is the part of the printer that touches the paste, and it is the part that is replaced most casually. Its material, its hardness and its edge condition decide how much paste is pushed into the aperture and how much is left behind.
What the Squeegee Does
The squeegee rolls the paste in front of the edge, fills the aperture and then shears the paste off the surface as it passes. The rolling action is what packs the aperture from the bottom up.
A soft squeegee rolls the paste well and a hard one scrapes the stencil clean. The correct choice is the one that fills the aperture without leaving paste on the stencil surface.
Material and Hardness
Metal squeegees hold their edge and give the most consistent volume over a long run. They are used for fine pitch and for lead free paste, and they require a stencil that can take the wear.
Polyurethane squeegees are softer and they conform to a slightly uneven stencil. They wear faster, and the wear is not uniform, so the print quality drifts across the panel. Our paste volume notes describe how the drift is measured.
Edge Condition
The edge must be straight and free of nicks. A nick leaves a line of unfilled apertures behind it, and the defect repeats in the same place on every board.
The edge should be inspected at the start of each shift and the squeegee replaced on a defined schedule rather than when the defect appears. The schedule should be written in the process documentation. Our fabrication notes notes list the attributes that should be stated.
Angle and Pressure
The angle between the squeegee and the stencil controls how the paste is pushed and how much pressure is needed. A steeper angle scrapes more and fills less, so the volume falls.
Pressure should be the minimum that clears the stencil completely. Excess pressure lifts the squeegee edge, wears the stencil and pushes paste under it, which produces a smear. The two settings should be developed together with a measured deposit.
Length and Coverage
The squeegee should be long enough to cover the printing area in one pass and short enough that the pressure is even. A squeegee much wider than the board wastes paste and concentrates the pressure at the ends.
Two squeegees are used where printing takes place in both directions, and both should be the same material and the same condition, or the two directions produce different volumes. Our paste inspection notes describe how the difference is detected.
Interaction With the Stencil
A hard squeegee and a thin foil wear each other. The stencil tension and the squeegee pressure together set how much the foil deflects against the board, and the deflection changes the contact area and the paste release.
Where the print is inconsistent across the panel, the squeegee and the stencil support should be checked before the paste is blamed. Our stencil notes describe the condition that matters.
Verification
The squeeze process is verified by measuring the deposit and by checking the stencil surface for paste left behind after the pass. Both are quick and both detect the fault before the boards are reflowed.
Where the volume is low on the leading edge of the panel and correct in the middle, the pressure or the stencil support is the usual cause. Our quality notes describe how the result is recorded.
Process Control and Verification
On a design of this kind, print quality is the item that decides how the rest of the board is arranged. The process window is set by the narrowest step in the flow, so an improvement anywhere else shows up as margin rather than as yield until that step is addressed. A short note on the drawing about handling, storage or packaging is often worth more than an extra decimal place on a tolerance.
Where a value sits close to a process limit, the drawing should say so, since the shop can then open the process window rather than working to a nominal figure that carries no tolerance. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used.
Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design. The measurements that matter are the repeatable ones: conductor width and spacing, annular ring, finished hole size, plating thickness and surface finish are all verifiable on a coupon that travels with the panel.
Running a first article through the same checks as the production panel confirms that the two agree, and that comparison is the cheapest form of process control available at prototype stage. Keeping a sample from the panel turns a dispute into a measurement, because the same coupon can be re-examined by both parties without rebuilding the batch.
Process Control and Verification
On a design of this kind, print quality is the item that decides how the rest of the board is arranged. The process window is set by the narrowest step in the flow, so an improvement anywhere else shows up as margin rather than as yield until that step is addressed. A short note on the drawing about handling, storage or packaging is often worth more than an extra decimal place on a tolerance.
Where a value sits close to a process limit, the drawing should say so, since the shop can then open the process window rather than working to a nominal figure that carries no tolerance. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used.
Process Control and Verification
On a design of this kind, print quality is the item that decides how the rest of the board is arranged. The process window is set by the narrowest step in the flow, so an improvement anywhere else shows up as margin rather than as yield until that step is addressed. A short note on the drawing about handling, storage or packaging is often worth more than an extra decimal place on a tolerance.
Process Control and Verification
On a design of this kind, print quality is the item that decides how the rest of the board is arranged. The process window is set by the narrowest step in the flow, so an improvement anywhere else shows up as margin rather than as yield until that step is addressed. A short note on the drawing about handling, storage or packaging is often worth more than an extra decimal place on a tolerance.
A first article check confirms that the process and the drawing agree on the points listed above, and that the coupon data supports the values used in the design.
Where a measurement falls outside the expected window, the sample is retained so that the cause can be established before the balance of the batch is released.
FAQ
Is metal always better than polyurethane? For repeatable volume on a fine pitch product, yes. For a warped board or a low volume application, a softer squeegee can compensate where metal cannot.
How often should the squeegee be replaced? On a measured schedule tied to the print volume, and immediately when an edge defect is found. Waiting for the defect to appear on production boards is too late.
What does gopcb provide for squeegee control? We provide material and hardness selection for the paste and the pitch, edge inspection and replacement schedule, angle and pressure development with measured deposit, length and coverage checks, and stencil compatibility review.
