How to set stencil printing parameters correctly
Stencil printing accounts for up to two thirds of all soldering defects in SMT assembly. This guide explains the four core parameters - squeegee pressure, print speed, snap-off and cleaning interval - and how to use them for an even solder paste deposit.
View soldering productsWhy does stencil printing decide solder quality?
In stencil printing, solder paste is pushed through the apertures of a stainless steel stencil onto the pads of the circuit board. The volume and shape of each paste deposit determine the later joints, because a deposit that is too small or smeared leads to opens, bridges or tombstoning.
Industry studies trace a large share of all soldering defects back to the printing process. The goal is a clean, defined paste volume with a transfer efficiency above 75 percent, measured as the ratio of the deposited volume to the theoretical aperture volume.
- Squeegee pressure: forces the paste into the apertures.
- Print speed: sets the fill time of each opening.
- Snap-off: the gap between stencil and board.
- Cleaning interval: keeps the stencil underside clean.
Setting squeegee pressure and print speed
Squeegee pressure is specified per centimetre of blade width and typically ranges from 0.2 to 0.5 kg/cm for metal blades. Too little pressure leaves paste sitting on the stencil and only partly fills the apertures, while too much pressure dips the blade into the openings and scoops the paste back out (scooping).
Print speed controls how long the paste has to flow into the openings. Common values lie between 20 and 100 mm/s. Fine-pitch components and small apertures require a slower speed so the paste fills the openings completely.
- Metal (stainless steel) blades are rigid and standard for fine pitch.
- A blade angle of 45 to 60 degrees governs how the paste rolls.
- If scooping appears, reduce pressure first, then check the speed.
Optimising snap-off and cleaning interval
Snap-off is the distance between stencil and board. At the recommended on-contact print, the snap-off is 0 mm: stencil and board sit directly on each other, and the stencil separates cleanly only as the table is lowered.
Separation speed should be slow and often stepped so the paste deposits do not tear. The cleaning interval defines how many prints run before the stencil underside is wiped - common values are 5 to 10 prints, or every print for very fine pitch.
Frequently asked questions
How high should the squeegee pressure be?
A useful guide is 0.2 to 0.5 kg per centimetre of blade width. The pressure is right when the stencil is wiped clean of paste after the stroke, without the blade dipping into the apertures.
What does snap-off mean in stencil printing?
Snap-off is the gap between stencil and board. The standard is on-contact printing with 0 mm snap-off, where the stencil rests directly on the board and separates in a controlled way as the table lowers.
How often should the stencil be cleaned?
Underside cleaning is common every 5 to 10 prints. For very fine pitch or small apertures, cleaning after every print may be needed to avoid smearing.
What is a good transfer efficiency?
Transfer efficiency is the ratio of deposited to theoretical paste volume. Values above 75 percent are considered good, and this requires an area ratio above 0.66 per IPC-7525.
Looking for stencil printing supplies?
We supply solder pastes, metal squeegee blades, cleaning systems and accessories for a repeatable, even paste deposit.
Process-safe
Parameters per IPC-7525 for stable transfer rates.
Repeatable
Defined deposits through matched squeegee pressure.
Cleanly printed
Cleaning systems prevent smearing.
Expert advice
Soldering specialists help you dial in the settings.