Sequencing is one of process planning, which refers to arrangement of components in their order of placement sequence and to prepare tape and reel by a sequencer. Sequencing is an important and integral part of effectively operating a printed circuit board (PCB) assembly system.
A PCB assembly system generally consists of different types of placement machines, testing equipment, and material handling equipment. In process planning stage, it requires to identify types of mixed technology PCB assemblies and their assembly sequence, and PCB assembly process sequence. A good sequencing process can reduce assembly time and improve productivity.
For handling high and rapid PCB assembly production demands, PCB and assembly manufacturers have employed high-speed surface mount machines into their SMT facilities. These pick-and-place machines have abilities of fast component placements, but provide challenges for process engineers to optimize the component placement sequences and feeder arrangements via effective planning.
In SMT optimization models, the combination of mounting, extracting, nozzle and feeder is the main key problem affecting the overall time of PCB assembly line.
In the mounting process, main factors influencing the efficiency of placement include:
- Component assignment
- Sequence of component placements
- Nozzle change
- Pick-and-place heads load
Therefore, minimizing the replacement times of nozzle, maximizing the heads load and arranging the location of the feeder reasonably and pick-and-place cycle of components can reduce the overall time of mounting process and improve the efficiency.
The optimization goal includes:
- the minimum nozzle replacement times
- the minimum pick-and-place cycles
- the minimum whole appropriateness degree of each pair of nozzles with the components
- the most optimal component placements sequence
- the least number of feeding
- the shortest moving distance