Solder Paste Jetting for Odd Shapes

What Paste Jetting Is

Solder paste jetting is a dispensing process that deposits paste onto a pad by firing a small droplet or a short pulse of material from a nozzle. There is no stencil, no squeegee, and no printing step. The machine moves over the board and deposits the paste exactly where it is needed, at a volume set by the process parameters.

The idea is not new, but its adoption has grown as board complexity has increased. A stencil is a fixed tool with one aperture pattern, and any change to the board requires a new stencil. Jetting is programmable, so a change is a software change, which makes it attractive for prototypes, high-mix production, and boards that would otherwise need several stencils.

The process also reaches places a stencil cannot. Fine apertures that print poorly, pads at different heights on a three-dimensional assembly, and small volumes that a stencil cannot deliver reliably are all candidates for jetting.

How the Process Works

Two mechanisms are common. In one, a piston pushes paste through a small nozzle in a controlled pulse, and the volume is set by the piston stroke and the nozzle diameter. In the other, a piezoelectric actuator generates a pressure pulse in the paste chamber, which ejects a droplet. Both require a paste that flows predictably through a small orifice and releases cleanly from the nozzle.

The deposit shape differs from a printed deposit. A jetted deposit is typically taller and narrower, and it may be applied as a single dot or as a pattern of dots that merge. That shape affects the reflow behavior, so the deposit pattern should be designed for jetting rather than copied from a stencil aperture.

Volume control is the central parameter. The machine adjusts the number of pulses and the pulse parameters to achieve the target volume for each pad, and the repeatability depends on the nozzle condition, the paste consistency, and the temperature. The nozzle has to be cleaned on a schedule, because dried paste changes the flow and the droplet size.

Where It Helps

The clearest case is high-mix, low-volume production where a stencil change between products would dominate the setup time. Jetting removes the stencil step entirely, so the line can switch products by loading a program.

The second case is boards with a small number of paste-deposited parts alongside many other processes, where making a stencil for a few pads is not economical. The third is three-dimensional assemblies, where the pads are not coplanar and a stencil cannot reach all of them at once.

Jetting is also used for repair and rework, and for adding paste to a board that has already been printed, which avoids a second stencil or a manual dispense. Where a single component needs a small volume late in the process, the jetting head can deliver it without disturbing the rest of the board.

Paste Formulation for Jetting

Not every paste jets well. The material has to flow through a small orifice without separating, release cleanly from the nozzle, and hold its shape after landing. A paste that is too viscous will not eject properly, while one that is too thin will produce satellites, which are small stray droplets around the deposit.

Paste suppliers offer formulations developed for jetting, with a controlled particle size distribution and a rheology that suits the pulse mechanism. Larger powder particles can block a small nozzle, so the particle size and the nozzle diameter have to be matched. The manufacturer’s specification for the nozzle and the paste should be followed rather than mixed.

The paste also has to remain stable in the machine’s reservoir. Jetting systems typically hold a small volume in the head, and the material is exposed to the machine temperature for a working period. A paste that dries or ages in the head will change the deposit volume, so the working life in the machine should be defined as part of the process.

Process Control

The output to control is the deposited volume and its position. Both can be measured with a paste inspection system, which is often integrated into the jetting machine or placed immediately after it. Volume that drifts points to a nozzle that needs cleaning, a paste lot that is aging, or a change in the machine temperature.

The nozzle is the wear item. It should be inspected and cleaned on a schedule, replaced when the droplet size drifts outside the control band, and protected during idle periods by a cover or a purge routine. A nozzle that is partially blocked produces deposits that are lower in volume and inconsistent, which appears as an intermittent defect.

The machine parameters that matter are the pulse duration, the pressure, the nozzle size, and the distance from the nozzle to the board. The distance is particularly important, because a change in the standoff changes the deposit shape. As with any dispensing process, the parameters should be recorded and the setup verified after any change to the machine or the product.

Limits and Comparison With Printing

Printing is still faster for a board with many pads. A stencil deposits all the pads in a single stroke, and no jetting head can match that throughput on a dense board. Jetting is therefore positioned where the volume is low or the mix is high, not where a single product runs in large numbers.

Jetting also deposits a different shape and a different volume range from a stencil. Very large deposits, such as those for a power pad or a thermal interface, are difficult to produce with jetting in a reasonable time, and a stencil remains the better tool for those. Very small deposits are where jetting excels, because a stencil has to be thin and a small aperture prints poorly.

The two processes can be used together. A stencil provides the bulk of the deposits, and a jetting head adds or adjusts specific pads on the same machine, which combines the speed of printing with the flexibility of dispensing.

FAQ

What is solder paste jetting? A stencil-free process that deposits paste onto pads by firing droplets or pulses from a nozzle, with the volume and position controlled by the machine program.

Is jetting faster than printing? No, for a board with many pads. Printing deposits all the pads in one stroke. Jetting wins where the volume is low, the mix is high, or the geometry cannot be printed.

Can any paste be jetted? No. The paste must be formulated for jetting, with a particle size and rheology that suit the nozzle. The nozzle and the paste should be matched according to the supplier’s specification.

What are satellites? Small stray droplets deposited around the main deposit, usually caused by a paste that is too thin or by nozzle parameters that are out of range. They can cause solder balls after reflow.

How is the process controlled? By measuring the deposited volume with a paste inspection system and monitoring the nozzle condition, the paste lot, and the machine temperature.

Conclusion

Solder paste jetting replaces the stencil with a programmable nozzle, which makes it valuable for high-mix production, three-dimensional assemblies, and small volumes that a stencil cannot deliver. It requires a paste formulated for the process, a nozzle that is maintained, and volume measurement to keep the deposits consistent. Where speed matters more than flexibility, printing still wins. For related topics, see our notes on SMT assembly, PCB assembly, PCB capabilities, and quality management for how paste is applied in 2026.