PCB Tech - How to ensure delivery of circuit boards

The short delivery cycle of the circuit board industry requires production management to control the entire production process from order placement to production completion. This requires the ERP system to provide production scheduling and work-in-progress management to ensure production delivery and customer response speed. Therefore, the most critical competitive advantage of PCB lies in: engineering research and development, production management, material control, manufacturing, outsourcing processing, etc., especially the WIP (work in process) control of on-site production management. If WIP is not properly controlled, there will be many mismanagement phenomena such as mismanagement, loss, stagnation, inaccurate WIP quantity, delayed replenishment, increased number of line changes, and unclear delivery dates.

The PCB industry has a wide range of products, which are generally distinguished by the number of layers, including single-sided, double-sided, four-layer, eight-layer, and ten-layer boards. The processing materials, process flow, process parameters, testing methods, quality requirements, etc. of PCB products will all issue processing instructions to the production department and outsourcing units through the preparation of production instructions (MI).

For products with four-layer boards and below, the process flow is relatively simple, and the production process card can be completed from the beginning to the end, and there is no need to change the process or replace the process card in the middle. As for the blind and buried vias products with more than six layers, because different inner and outer layers have different circuit diagrams, process flow or process parameters, and use different molds, film and other auxiliary equipment, different productions are required. Instructions and related documents will also produce different production process cards during the production process to control the manufacturing process and quantity of different inner and outer layers.

In the production process, the multilayer board will have different inner codes, which must be distinguished by different codes during the production process, and different production process cards are used to control the production progress. PCB is the transfer and handover of auxiliary products through the production of batch cards (LotCard), commonly known as excess. Due to the large number of online products and the complicated models, it requires simple, fast, and fault-tolerant operations for counting operations, scrapping operations, and repairing operations. During the implementation process, I deeply felt that general-purpose ERP products were basically unable to deal with the business of separate encoding, separate over-numbering, separate scrapping, and separate replenishment of the inner and outer layers.

Generally speaking, the more detailed the production operation plan, the richer and more valuable the information it gives, and the more difficult it is to calculate it accordingly. The rougher the production plan, the less information and the lower the value. However, the process flow involved in PCB is often more complicated. The engineering data and MI production of a complex PCB multilayer board often takes a long time to complete, and the delivery time required by customers is often very tight. For the production management operation of the PCB manufacturing industry, it is a process-based manufacturing method, so it will adopt the small scheduling (Run Card scheduling) management technology. Therefore, the following PCB production process characteristics must be paid attention to when scheduling:

Reflow processing

PCB processing is a more representative process-based processing, which is different from the mechanical assembly processing mode. It mainly consists of a raw material input, and the subsequent auxiliary material input and processing technology are processed around the main raw material. And due to the emergence of multi-layer board technology, reflow production (that is, repeating a certain process or a certain period of processing) in the PCB industry has become more and more common.

Cutting and pressing

Whether it is the substrate processing in the front section or the output of the PCB board in the rear section, one of the links that must be experienced is continuous cutting. The original fabrics invested in the first stage are all large-scale original fabrics. In order to meet the needs of subsequent processing during continuous processing, they will be continuously cut into reasonable sizes for subsequent processing. The other process is pressing. Whether it is processing the substrate at the front stage or the multilayer board at the back stage, pressing work is required, that is, two boards with the same area and shape are pressed into one piece. This is particularly obvious in the case of multilayer board pressing. .

For the characteristics of cutting and pressing, that is, how many raw materials are needed to process a certain number of finished products, the number of large plates is converted into the number of small plates, and the input of raw materials is calculated from this. However, when there is a waste/waste situation, combined with the ratio of the materials used in the father and son work orders, sometimes it will cause the increase in the workload of the PCB factory and the unsmooth and inconsistent process.

Single chip scrap

Different from scrapping in the assembly industry, PCB scrapping includes so-called single-chip scrapping in addition to scrapping (rejecting scrapped products). The reason is that the pressing process is usually carried out for a large board, and a large board generally produces a different number of final single-piece products. When a defect occurs in the pre-pressing process, causing a certain point on the single panel A or B to be of poor quality, the production staff cannot simply discard the large panel, but continue to use the material, but will record for the single panel The number of scraps of a single chip.

For example, a large board A can be finally cut into 16 small PCB boards, and due to process problems in the current processing process, a certain point on the board is damaged. Therefore, the result of this batch processing is that the number of scrapped boards is 0 ( There is no whole piece scrap), and the single piece scrap is 1. This quantity will be accumulated backwards along with the process flow for production statistics and final product output. At this time, it should be noted that the number of single-chip scraps will be inherited by the double-layer board after passing through the compaction industry. Because after single panel A and single panel B are pressed together, the projection of the dead pixels on board A on B will also cause dead pixels. The resulting double-layer board will also be unusable at this point, and the same number of single chips will be formed. The number of scraps.

Finally, the PCB industry is a kind of foundry industry, and the design changes of products are very frequent, and versions are often changed. Once the customer changes the version, the manufacturing instructions and process flow cards must also be changed, and there may even be some changes and some no changes.