Learning objectives
- Describe how pick and place machines pick, centre and place components into paste
- Verify feeders, reels and splices before and during a run
- Explain how placement force, nozzle condition and vision centring affect quality
- Run a first article inspection before releasing a lot to production
Lesson
Placement is the fastest stage on the line and the easiest place to build a fault into every board. High speed chip shooters place the small parts and flexible mounters place the larger and odd shaped parts. Vacuum nozzles pick each component from a tape reel, tray or tube, the vision system centres the part on the nozzle and finds the board fiducials, and the machine sets the part down into the wet paste with controlled force and height. Modern machines place with accuracy measured in tens of microns, but that accuracy only helps if the right part arrives at the right pad the right way up.
Feeder discipline is the operator’s real craft. Every feeder slot must carry the part number the program expects, verified by label, barcode or RFID checks built into the line. Reels run out and are spliced so production never stops, and a splice is exactly where a wrong reel can enter the line. The classic trainee error, repeated in factories everywhere, is bypassing feeder verification after a splice or a changeover because the line is waiting. Polarity is checked at the same time, because a reversed diode or capacitor placed at full speed is a defect manufactured with great precision. Placement force matters as well. Too much force squeezes paste out from under the part and invites bridging, while worn or wrong nozzles drop parts, damage terminations and throw placement off centre.
Before any lot is released, the first article is inspected. The first completed board is compared against the bill of materials and the assembly drawing under magnification, checking values, positions and polarity, and only then does the run begin. James Onsomu writes in his PCB quality book that automated pick and place machines enhance precision and speed, that technicians must be well trained to run them because incorrect placements lead to malfunctioning circuits, and that regular calibration and maintenance keep the machines accurate. On double sided boards the second side is placed on a second pass, with the first side already reflowed, and the operator confirms the program and support match that reality before the first panel runs.
Key numbers
- Placement accuracy: measured in tens of microns on modern mounters
- Feeder verification: every feeder and every splice confirmed against the program before running continues
- First article: every placement on the first board checked against the bill of materials and drawing before the lot is released
- Placement force and height: set per component so paste is not squeezed out from under the part
Defects to spot
- Missing components: pick up failures, vacuum loss, or empty feeder pockets
- Shifted or skewed parts: vision centring faults or worn nozzles
- Wrong part or wrong value: feeder loaded with the wrong reel, usually at a changeover
- Reversed polarity: verification skipped after a splice or reel change
- Dropped or flying parts: nozzle damage or vacuum problems
- Damaged terminations: rough handling or wrong nozzle for the package
Stage check, self test
Answer each question, then open the answer to check yourself. Passing standard: 80 percent, at least 4 of 5 correct.
1. What is the classic trainee error at placement?
A. Cleaning the nozzles too often
B. Bypassing feeder verification after a splice or changeover
C. Running the first article inspection twice
D. Checking polarity before the run
Show answer
Answer: B
2. What can excessive placement force do?
A. Improve paste wetting
B. Centre the part perfectly
C. Cool the paste
D. Squeeze paste out from under the part and invite bridging
Show answer
Answer: D
3. What is a first article inspection?
A. Comparing the first completed board against the bill of materials and drawing before the lot runs
B. Inspecting the last board of the day
C. Reading the machine manual
D. Checking the packing boxes
Show answer
Answer: A
4. A reel runs out mid run and a new reel is spliced in. What must happen before production continues?
A. Nothing, splices are always correct
B. The splice is hidden so the supervisor does not see it
C. The new reel and part number are verified against the program
D. The line speed is doubled to catch up
Show answer
Answer: C
5. Modern mounters place with accuracy measured in what range?
A. Centimetres
B. Millimetres
C. Tens of microns
D. Metres
Show answer
Answer: C
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