Placement Nozzle Wear: Vacuum, Alignment and Pick Reliability

The placement nozzle is the last element in the machine that touches a component, and its condition decides whether the part is picked, held through the move and released in the right place. A nozzle that leaks vacuum or has a worn tip produces placement faults that are then attributed to the vision system or to the feeder. The machine reports a pick error only when the part is dropped, and reports nothing when the part is held slightly off centre.

Three properties carry the influence: the vacuum the nozzle can hold, the geometry of the tip, and the alignment of the nozzle axis with the spindle. Each degrades slowly, and each can be measured before it produces a defect. Together they set the component placement result more often than the vision system does.

What the Nozzle Has to Do

The nozzle has to pick a component from its packaging without moving it, hold it through an acceleration profile that can reach several g, and release it onto a paste deposit without disturbing the paste or the part. It does all of this through a vacuum path only a few millimetres long. The move is where the force is highest, because acceleration acts on the component as well as on the nozzle.

The pick is a balance between force and disturbance. Too little vacuum and the part shifts during the move, while too much can damage a small part or deform a soft tape as the nozzle descends. The right level is found by measuring the placement result rather than by raising the vacuum until parts stop dropping.

Vacuum Level and Leakage

The vacuum at the nozzle is lower than the level at the pump, because the path leaks air at every joint. The difference is small on a new machine and grows as seals harden, as tubing ages and as the rotary union wears. Every joint in the path is a candidate, and the ones inside the spindle are the hardest to reach.

The measurement that matters is taken at the nozzle rather than at the pump. A gauge on the pump reports the condition of the pump, while a reading at the nozzle reports the whole path and is what the component actually experiences. The two readings together give the pressure drop across the path, which is the number that changes as parts age.

Tip Condition and Nozzle Wear

The tip is made of a material chosen to resist abrasion from the component and from the tape. It wears by losing its flat land, by collecting a ring of adhesive or flux, and in the worst case by chipping at the edge. A tip that has collected a ring of adhesive has a larger contact face and a smaller effective vacuum.

A worn tip loses vacuum at the contact face, so hold force falls even when the pump is healthy. A contaminated tip is worse, because the contamination is often conductive and can transfer to the component. A chipped tip holds a large part acceptably and fails on the smallest component in the product.

Alignment and Centering

The nozzle has to be concentric with the spindle axis, and the component has to be centred on the nozzle. Both are checked with a calibration target, and both change after a crash or after a nozzle change that was not seated correctly. The check uses a target the vision system can see, so the two halves of the machine are aligned to each other.

A centring error of a few tens of micrometres is absorbed by the vision correction on a large component and is not absorbed on a small one, because the correction has a limit and the tolerance is tighter. The error also varies with the angle of the nozzle, which is why a bent shaft produces an error that changes with rotation.

Component Damage and Force

The force applied during placement is set by the machine and transmitted through the nozzle. A nozzle that is too small for the component concentrates that force and can crack a body or a termination. The symptom appears as a crack after reflow rather than at placement, which makes it harder to attribute.

The same applies during the pick, when the nozzle descends into the tape. A worn tip with a sharp edge can mark a component or lift a cover tape in a way that disturbs the next part in the pocket. The disturbance is worse on a tape with a soft cover, which is also the tape whose pocket geometry varies most.

Nozzle Selection by Component

Nozzle selection is a table rather than a guess. Each component size and body type has a nozzle that suits it, and the table belongs to the setup for a product rather than to a decision left to the operator at the machine. The table is checked at changeover, like any other setup item, rather than when a defect appears.

Using one nozzle for everything is common on prototypes and is a source of intermittent faults in production. The variation appears as a pick rate that falls on one component while the rest of the line runs normally.

Cleaning and Maintenance

Cleaning is scheduled and covers the tip face, the bore and the seal at the spindle. The bore is where a build up of adhesive reduces the effective diameter and changes the hold force without any visible wear at the tip. Cleaning a bore means removing the nozzle, and that is a good moment to inspect the seal.

Maintenance also covers the tubing, the rotary union and the vacuum generator. A tube that has hardened or been kinked during a service visit is a leak that no amount of tip cleaning will correct.

Measuring Pick Accuracy

Pick performance is measured as a rate over a run rather than as a single result. The machine reports pick errors, and the trend of those errors by nozzle and by feeder position identifies the element that is degrading. A single measurement after cleaning says very little, while the same measurement every week says a great deal.

A vacuum check at the nozzle, taken at the same interval as the cleaning, gives the trend that explains the pick errors. The measurement is quick and it needs a gauge rather than a service call.

Records and Change Control

The record holds the nozzle identity, its installation date, the vacuum reading at each service and the pick error rate attributed to it. With those fields, a falling pick rate can be traced to a nozzle rather than to a feeder or a tape.

Nozzle changes are recorded as setup changes, because a replacement that is nominally identical but from a different batch can perform differently. The placement side of the same question is described in the notes on placement offset control, the force side in the notes on placement force, and the vacuum path itself in the notes on vacuum nozzle care.

FAQ

Does a higher vacuum always give a better pick? Up to the point at which the force damages a small component or deforms a tape. The level is matched to the part being picked.

Can a worn nozzle be refaced? Some can be dressed within a defined limit, and that limit is set by the tip geometry the nozzle was designed with.

How often should a nozzle be cleaned? On a scheduled interval and after any run with an adhesive-bearing tape, which leaves a deposit that hardens on the tip face.