Switching Period and Particularity of PCB Assembly

The assembly of electronic products has brought huge challenges to production operation scheduling due to its large number of components, wide variety, and short life cycle of electronic products. Multi-variety, small-batch, and variable batch has become the mainstream production mode of electronic manufacturing. In this mode, the switching time between multiple varieties occupies an increasing proportion in the entire assembly time.

It is composed of a high-speed placement machine and a multi-function placement machine. In fact, the entire PCB assembly line also includes equipment such as board feeders, screen printing machines, dispensers, reflow soldering and curing ovens, and board take-up machines. These devices are connected in series to form PCB assembly line, but these auxiliary equipment are not It does not constitute the bottleneck process of the entire pipeline, so it is omitted when modeling. Each placement machine can accommodate 20 feed slots, and each component occupies one feed slot on the placement machine. Generally speaking, the number of component types required for a single variety PCB does not exceed the capacity of the feeder, but the total number of component types required for multi-variety PCBs usually exceeds the capacity of the feeder.

During the mounting process, the components required by different types of PCBs are placed on these feed troughs, and the pick-and-place device removes the components from the feed troughs and places them on the PCB at the specified location. According to the survey data of the empirical research objects, the average time for the high-speed placement machine to mount a component is 0.06s, and the average time for switching a feed slot is 180s. The multi-function placement machine has two worktables, but only one worktable works, and the other worktable is only used to place large or special-shaped components. Each worktable accommodates 10 feed troughs. The average placement of a component requires 0.18s The average time to switch one feeder is 220s. When switching between different types of PCBs, the placement machine requires a certain preparation time for switching, usually about 6 times the time for switching a component feed tank, that is, the 1200s. It can be seen that the switching time plays an important role in the assembly process of electronic products.

In a multi-variety and small-batch environment, PCBs are usually grouped first, and PCBs with similar characteristics are grouped together so that in the same group, assembly between different types of PCBs does not require replacement of the feeder, nor does it require Switching time; but when the feeder needs to be replaced between the two groups of PCBs, you need to consider the switching time between them. According to this, the PCB production scheduling problem is divided into two levels: the first level scheduling problem is called "board level" scheduling problem, that is to determine the production sequence between each PCB within a PCB group; the second level scheduling problem is called For the "group-level" scheduling problem, that is to determine the production sequence between PCB organizations.

The above information is provided by the power electronics PCB board supplier.