Nozzle Clogging: 5 Causes and How to Prevent Them

Nozzle clogging is the partial or complete blockage of the dispensing orifice, and on a jetting or dispensing machine it produces a missing or undersized deposit rather than a machine fault. The valve keeps firing, the program keeps running, and the board leaves the machine with a gap the operator did not see. Because the blockage often clears itself, the defect can be intermittent and hard to reproduce.

This guide covers five causes of nozzle clogging, the measurements that detect a partial blockage before it prints, and the cleaning routine that keeps a jetting valve reliable. It applies to jetting valves and to time-pressure dispensers with fine needles.

What Nozzle Clogging Looks Like

A blocked orifice produces three distinct signatures. A full blockage produces no deposit at all, so the paste inspection system reports a missing dot. A partial blockage reduces the dot volume, and the reduction is gradual enough that a limit is the only way to catch it. A blockage at the edge of the orifice distorts the dot, producing a crescent or a tail.

The distortion signature is the one that escapes most often, because the dot is present and its volume may be within the limit. The shape, however, is wrong, and a distorted dot releases poorly and can bridge to a neighbouring pad. Detection therefore needs a shape check as well as a volume check.

Cause 1: Paste Viscosity Drift

A paste whose viscosity has risen flows less readily through a small orifice and leaves a residue on the nozzle face after each shot. That residue dries, the next shot deposits onto it, and the blockage builds. Paste viscosity drift is usually caused by solvent loss from an open syringe or by a rise in the ambient temperature.

The control is to keep the syringe closed when it is not firing, to hold the paste at the temperature the maker specifies, and to weigh the first dots of a shift. Where the dot volume falls without any change to the valve settings, the paste is the first suspect rather than the nozzle. Our notes on paste storage cover the conditions that slow the drift.

Cause 2: Particle Size Against Orifice Diameter

Paste is a suspension of alloy powder, and the largest particles set the minimum orifice the paste can pass. A common working rule is that the orifice should be at least four times the largest particle diameter, and a paste with a coarse powder will block a small nozzle even when the paste itself is in good condition.

The paste grade should be chosen for the orifice rather than the other way round. Where a fine orifice is needed for a small dot, a type 5 or finer powder is required, and the metal load may have to be reduced to keep the paste flowing. Mixing two grades of paste to make a batch work defeats the purpose and reintroduces the coarse particles.

Cause 3: Dwell Time Between Dots

A valve that fires continuously stays warm and its nozzle stays wet. A valve that stops for several minutes between boards cools, and the paste on the nozzle face dries. Dwell time is therefore a cause of clogging that appears at the start of a batch rather than in the middle of one.

The remedy is a purge routine at each stop, or a park position that keeps the nozzle in contact with paste rather than air. Where the machine supports a periodic dummy shot, it should be programmed to fire at an interval shorter than the time it takes the paste to skin over, which is measured rather than assumed.

Cause 4: Nozzle Cleaning and Storage

A nozzle that is cleaned with a wire or a hard tool is damaged, and the damage creates a place for paste to collect. A nozzle that is stored dry accumulates dried paste inside the orifice, and the first shots of the next shift are short until the material clears.

Cleaning should follow the maker’s method, which usually means a soft wipe of the face, a purge, and a solvent soak for the tip only when it is removed. The nozzle should be stored in the condition the maker specifies, which is often with a protective cap rather than bare. Our preventive maintenance schedule is the place for the interval.

Cause 5: Temperature Control at the Valve

The valve body is heated on many machines so that the paste stays at its working temperature. A heater that has drifted, or a thermocouple that has come loose, changes the paste temperature at the orifice, and the effect on viscosity is large over a shift. Temperature control is therefore part of the clogging question rather than a separate topic.

The valve temperature should be measured at the nozzle body rather than read from the controller, and the measurement should be recorded with the settings. A change of more than a few degrees should be investigated before the paste or the nozzle is blamed, because the heater is the cheaper item to check.

Detecting a Blockage Before It Prints

The most effective control is a measurement after deposition. A paste inspection system that checks dot volume and dot shape catches a partial blockage on the first board it affects, and the machine can then purge and re-run the board. Where the machine has no inspection, a weigh check on a test card at defined intervals gives a slower but still useful signal.

The trend matters more than the individual reading. Where the dot volume falls by a few percent over an hour and then recovers after a purge, the blockage is building and clearing repeatedly. Recording the dot volume with the purge events turns an intermittent defect into a visible pattern. Our notes on paste inspection cover the measurement setup.

Cleaning Routine and Records

A workable routine covers four points: a face wipe at every stop longer than a defined interval, a purge at the start of each shift and after each break, a solvent soak of the tip on a weekly interval, and a replacement of the nozzle when the dot volume can no longer be recovered by cleaning. Each point should have a record, because a routine that is not recorded is a routine that is skipped under pressure.

The nozzle’s life should be tracked in shots rather than in days, in the same way as a placement nozzle. Where a valve consumes nozzles faster than expected, the paste grade, the valve temperature and the dwell pattern should all be reviewed before the nozzle specification is changed. The wider practice for paste handling is described in the standards published by IPC, and the shop’s own interval should be set from its own data.

FAQ

Can a clogged nozzle be cleared in place? A purge will clear a soft blockage, and a hard blockage usually needs the tip to be removed and soaked. Poking the orifice with a wire clears it temporarily and damages the edge, which produces a distorted dot afterwards.

Does a larger nozzle solve a clogging problem? It reduces the sensitivity to particle size and to dried residue, at the cost of a larger minimum dot. Where the pad needs a small dot, the paste grade should be changed instead.

How often should the nozzle be replaced? When cleaning no longer restores the dot volume and shape, or at a shot count set from experience with the valve. A nozzle is a consumable and should be treated as one rather than run until the line stops.