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1. Switching time and particularity of PCB assembly
The assembly of electronic products has brought huge challenges to production operation scheduling due to the large number of components, variety and short life cycle of electronic products. Multiple varieties, small batches, and variable batches have become the mainstream production mode of electronic manufacturing. . In this mode, the switching time between multiple varieties occupies an increasing proportion of the entire assembly time.
It consists of a high-speed placement machine and a multi-function placement machine. In fact, the entire PCB assembly line also includes board feeders, screen printers, glue dispensers, reflow soldering and curing furnaces, and board receivers. These devices are connected in series to form the PCB assembly line, but these auxiliary equipment are not It does not constitute the bottleneck process of the entire pipeline, so it is omitted in the modeling. Each placement machine can accommodate 20 feeding slots, and each component occupies one feeding 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 a multi-variety PCB usually exceeds the capacity of the feeder.
During the mounting process, the components required by different types of PCBs are placed on these feeding troughs, and the pick-and-place device removes the components from the feeding troughs and mounts them to the designated positions on the PCB. According to the survey data of the empirical research object, the average time for high-speed placement machine to place a component is 0.06s, and the average time for switching a feeder is 180s. The multi-function placement machine has two workbenches, but only one workbench works, and the other workbench is only used to place large or special-shaped components. Each workbench can accommodate 10 feeding troughs. It takes 0.18s to mount a component on average., The average time to switch a feeder is 220s. When switching between different types of PCBs, the placement machine requires a certain amount of preparation switching time, which is usually about 6 times the time of switching a component feeder, that is, 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, the PCBs are usually grouped first, and the PCBs with similar characteristics are divided into one group. In this way, in the same group, the assembly of different types of PCBs does not need to replace the feeder, nor does it require Switching time; but when the feeder needs to be replaced between the two sets of PCBs, the switching time between them needs to be considered. According to this, the PCB production scheduling problem is divided into two levels: the scheduling problem of the first level is called the "board-level" scheduling problem, that is, determining the production sequence among PCBs in a PCB group; the scheduling problem of the second level is called It is a "group-level" scheduling problem, that is, determining the production sequence between PCB organizations.
Second, the solution after the circuit board is plugged
1. Customers often design VIA holes with green oil on both sides without windows or partial green windows, which is a headache for the circuit board. Or single-sided windows. What should I do with this design?
2. The first consideration is what kind of surface treatment the circuit board uses. If it is sprayed tin (HA LS, I must prevent the use of single-sided plug hole technology, because the depth of single-sided plug hole is low, which is easy to cause plugging during tin spraying. Tin beads, plug tin beads have a great influence on the appearance.
3. If the circuit board is treated with other external surfaces, such as immersion gold, OSP, immersion silver, etc., single-sided plug holes can be accepted. After considering the above factors, let's look at the customer's green oil window design. If it is partially opened, it should be Try to prevent the use of green oil cover hole edges and allow green oil to enter the hole, because this method is also easy to cause tin beads.
4. Combining the above two situations, the best treatment is to double-sided plug holes, or green oil cover hole sides, allowing 1-2MIL tin ring disposal methods are most welcome for circuit boards. Of course, the oil plugging situation here is for Ordinary photosensitive oil is not a heat curing oil.
