Placement Nozzle Wear: Vacuum Level and Pickup Reliability
A pick-and-place machine reports a missed pickup as a count, not as a cause, and the cause is usually in the nozzle tip: a worn face, a partial blockage, or a vacuum level that no longer matches the part being placed. None of these produces an obvious alarm, which is why pickup reliability has to be measured rather than watched.
How a Nozzle Fails
A nozzle tip is a soft, precisely ground surface that contacts every part it places, and it wears by abrasion against the tape, the feeder and the part surface. The wear shows first as a polished ring on the tip face, then as a loss of flatness, and finally as a burr or a chipped edge. Each stage reduces the contact area that holds the part while the machine moves.
Wear is not the only mechanism. Solder paste, flux vapour and paper dust build inside the orifice and reduce the effective opening, which lowers the vacuum that reaches the part. A blocked nozzle behaves like a worn one, and both produce the same symptom, so the diagnosis has to separate the two before any part is replaced.
Vacuum Level and Part Size
Vacuum is specified as a pressure difference, typically minus 40 to minus 70 kilopascals at the nozzle, and the requirement scales with the part. A 0402 chip of roughly 0.4 milligrams needs far less holding force than a large connector, but it also leaks more around its edges, so the required flow is often higher for the smaller part. The machine’s vacuum sensor threshold should be set per nozzle and per part family, not globally.
The relevant parameter is the vacuum measured while the part is held, not the pump’s free-air rating. A pump that pulls 70 kilopascals on a sealed nozzle may deliver only 25 kilopascals at a 0402 chip because of leakage around the tip. Measure at the tip with the part in place, using a test fixture that mimics the real part size.
Tip Inspection and Wear Measurement
Inspect tips on a schedule under magnification and measure the face, not just the orifice. Check the outer diameter, the flatness of the tip face and the roundness of the orifice, and compare against the new-part drawing. A useful limit is 0.05 mm of material loss on the tip face or any visible burr, after which the tip is removed from the head rather than rotated to a coarser part.
Record the measurement per nozzle serial number so the wear rate is visible. A tip that goes out of tolerance in two weeks points to a mechanical problem, such as a bad nozzle holder or a feeder height error, while one that lasts a year is behaving normally. Without a record, tips are replaced on suspicion and the root cause survives.
Pickup Position and Part Presentation
Most pickup failures are actually presentation failures. If the tape pocket sits low or high in the feeder, the nozzle either crushes the part or approaches too far away to seal, and both produce intermittent misses. Pick height is normally set 0.1 to 0.3 mm below the part surface, and dwell is 30 to 60 milliseconds, short enough to keep cycle time and long enough to build vacuum.
Tape pocket depth, cover tape peel force and feeder height all drift with wear. When a feeder starts producing misses on one part number while adjacent lanes are fine, the feeder rather than the nozzle is the prime suspect, and swapping the feeder is the fastest way to confirm it.
Nozzle Types for Small Chips and Odd Forms
Small chips are picked with a flat tip that is smaller than the part outline but large enough to seal, while larger chips and odd-form parts use tips with a recess or a rubber pad. Using a tip that is too small gives a leak; using one that is too large picks up adjacent parts or lifts the pocket. The correct tip for a given part is a specification, not an operator preference.
Fine-pitch and thin parts also need a tip material that does not mark or charge the component. Conductive or dissipative tips prevent static damage on sensitive devices, and soft tips reduce mechanical marking on parts with a fragile surface. Both properties change the wear rate, so the maintenance interval has to follow the tip type.
Detection: Missed Pickup Sensors and Vision
Vacuum sensors detect a miss by the pressure change that occurs when a part seals the tip. The threshold has to sit between the vacuum with a part held and the vacuum with the tip open, otherwise the sensor either reports false misses or accepts an unsealed tip. Re-teach the threshold whenever a nozzle or part family changes, and verify with a deliberate miss.
Vision adds a second check by looking at the part after pickup, which catches a tilted part that still seals. Neither sensor catches a part held so weakly that it shifts during the move, so placement accuracy data remains part of the picture: a pickup problem often appears first as a placement offset on one head.
Cleanliness, Static and Sticking Parts
A nozzle that picks up paste or adhesive loses vacuum and marks the next parts. Clean tips on a documented interval with the approved solvent, and never scrape the orifice with a metal tool, which changes its diameter. Clean the whole head, because dust drawn through a leaking tip settles in the vacuum path and slowly reduces flow.
Static is the other hidden mechanism. A charged part can be attracted to the nozzle before the machine intends to pick it, or repelled and dropped after a nominal seal. Grounding the nozzle, using dissipative tip material and controlling the ionizer at the feeder all address this, and the symptom is the same intermittent miss that a vacuum problem produces.
Maintenance Schedule and Spare Strategy
A workable schedule inspects tips on a fixed interval, verifies vacuum thresholds weekly, and replaces rather than downgrades. Keep a small spare set of each critical nozzle size in stock, because a worn tip that is out of tolerance cannot be repaired on the line and running it on coarse parts only postpones the failure.
Track replacement by nozzle and by head so a single position that consumes tips faster than its neighbours is visible. That pattern almost always points to a mechanical issue in the holder or a feeder height problem rather than to the tips themselves.
Verifying Pickup Reliability by Measurement
Pickup reliability is a rate, and it can be measured from the machine’s own counters: the number of missed pickups per thousand placements, split by part family and head. A rate that is stable but elevated points to a systematic issue; a rate that is climbing points to wear. Comparing the two heads of a machine is often the fastest diagnostic available.
For a tighter check, run a pickup trial with a known part count and no board loaded, then weigh or count the rejects. The resulting number can be compared against the placement accuracy data to confirm that the machine is picking and placing as specified rather than merely reporting that it is.
Related reading: our fabrication notes, board quality and design release notes cover the same ground.
FAQ
What vacuum level should a placement nozzle hold? Set the requirement at the tip with the part held, typically minus 40 to minus 70 kilopascals. Small chips leak more, so their required flow can be higher than a large part.
When should a placement nozzle be replaced? At roughly 0.05 mm of material loss on the tip face, or on any visible burr or chipped edge. Rotating a worn tip to a coarser part does not restore performance.
Why does a nozzle miss on some parts and not others? Part size changes the seal and the leak rate, so a marginal tip or threshold fails first on the smallest chips. Feeder height and pocket depth have the same effect.
