The component leads must be accurately immersed in the solder paste previously deposited on the PCB pads.
Higher placement accuracy requires help from local fiducials visualized by optical or laser sensors.
Flexibility involves the aspects of component variety, number of feeders and PCB size range.
[1] There are two major types of pick and placement machine: Chip shooters are being used for as much as 90% of the most common components, like passives and small actives.
Comparing to chip shooters, flexible placers are slow (6,000 to 40,000 per hour) with a high accuracy (as low as 25 μm).
Chip shooters and flexible placers are typically combined to use and they can take account of nearly 65% of the total assembly line cost.
During the sequence, the beam moves perpendicular to the direction of the placement head movement, which offers two degrees of freedom (X and Y alignment) in a plane parallel to the machine table.
Sometimes a secondary vision system is also applied to check the correctness and alignment of the components after pick-up and before placement.
As the PCB and feeders remain stationary in the placement sequence, the additional sources of positional inaccuracy are eliminated.
Comparing to a gantry head, the simultaneous movements of feeders and PCBs greatly improve the average placement rate.
Because passive components do not demand a great placement accuracy, it is exclusively applied in chip shooters.
A high product mix and correspondingly small batch sizes result in frequent feeder changing.
Tape feeders come in a variety of sizes and can be used for Small-outline integrated circuits (SOICs) and plastic leaded chip carriers (PLCCs).
Especially in the case of small chip devices, the tape waste material weighs several times more than the packaged components.
Due to the various possibilities of adjusting the size of the lane, the feeder can easily be adapted to many different component types.
This process is often slower compared to tape feeders as the components fed in matrix trays often require higher level of placement accuracy.
It could also enabling total assembly solutions with much higher speed and flexibility, resulting in lower cost per placement.
In addition, it could eliminate costly processes such as intermediate die transfer into pocketed tape, surf-tape, or waffle packs prior to placement.
In practice it is not possible to obtain the quoted theoretical maximum throughput rate for machines in a placement system.
It is necessary to derate the theoretical numbers to obtain realistic values, due to unexpected downtime, board load and unload time and machine configuration.
To calculate the amount of global or system derating, one should take the average of the number of total components placed per hour in a long period (i.e. an entire product shift).
Regularly scheduled stops should be included when determining the level of global derating the system requires.
Rigorous derating, which considers each piece of equipment in service for a particular product individually, must be conducted by specific machine model for the line balancing.