The initial situation can be described as follows:
The process starts with the manufacturer taking receipt of an order for electronic printed circuit boards, where the number of required SMDs is calculated. These are either already in stock or must be specially ordered. The expected production date is then determined based on this data. A final automatic check is carried out in the ERP system shortly before this date to ascertain whether all the components are actually in stock.
The SMDs are mostly made in Asia. It is therefore often necessary to keep larger supplies in stock due to the long transport route.
In addition, the reels on which the SMDs are stuck come in various formats. Their diameter can be anything between 7 and 22 inches and their width ranges from 10 to over 200 millimeters. Depending on these dimensions they can be stored away next to, on top of, or behind one another. This calls for a flexible storage system in terms of:
- the tray height so that access to reels stored in two rows is also guaranteed
- the width of the holders in trays for the various formats
- special requirements (the storage of sensitive SMDs in dry boxes)
SMD reels can be stored in a number of different ways. The most essential thing is to ensure that the components are kept in conditions that avoid electrostatic charge in order to prevent any damage.
Another ever more frequently occurring problem is the increase in the number of moisture-sensitive components. Accordingly, it is important to avoid any potential ingress of moisture which increases the likelihood of damaging the components during the soldering process. This risk can be avoided by storing the components in suitable dry boxes or maintaining a modified and controlled atmosphere in the storage systems.
When storing the incoming reels, they are scanned andentered into the ERP system with information such as delivery date as well as order and material data.
Based on the number of printed circuit boards produced, two different groups and specification profiles can be assumed in relation to SMD handling:
- Producers of large quantities with short storage throughput times. They can more easily access standard storage technology and software solutions than
- Producers of small batches and prototypes. Due to the often small quantities involved, they face more complex storage challenges:
- with SMD reels, only the standard components are kept in stock. Other SMD components are only ordered once an order has been received
- these SMD components are only stored temporarily
- the increased storage complexity results in greater demands being placed on the order picking and ERP
If all the components needed for a production order are in stock, the order-related picking process can begin.
The SMD reels are requested via the ERP system as soon as they are needed for production. The reels are retrieved from the storage unit, removed from the trays/shelves, and then manually loaded onto the feeders. This is standard practice whereby the process of retrieving the reels is separate from that of loading the feeders. Manual intervention is necessary here, because it is currently difficult to find an automatic solution to the process of threading the SMD reels. The feeders are then taken to the production areas and placed in their designated positions.
Another way is the simultaneous retrieval and loading of reels onto the feeders, which saves a considerable amount of time and money, but calls for a high level of storage automation and thus higher investment costs.
The SMD reels can also be removed fully automatically from the trays and transported for further processing where they are manually loaded onto the feeders and made available.
As soon as the SMDs are made available in the production area, the robots grab the components from the reels and solder them onto the printed circuit boards. This involves the components being removed using vacuum pipettes or picker arms and then positioned on the circuit board and soldered into place. This process is repeated for all components. Once a circuit board has been fully populated, it is replaced by the next one. After this process the circuit boards are then given a protective coating if necessary. The fully populated circuit boards subsequently undergo a series of tests and functional checks.
4. Returning goods to storage
Once the process has finished, the ERP system provides detailed information on:
- used SMDs
- rejected SMDs (picking errors) or
- damaged SMDs
This process is known as “back flushing”. Detailed information on the remaining quantities is now recorded in the ERP system. Afterwards, the SMD reels are:
- returned to storage
- transported to the next production unit