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HomeNewsApplication of MES System Based on Dynamic Quality Control in PCB Board Assembly Industry

Application of MES System Based on Dynamic Quality Control in PCB Board Assembly Industry

2019-06-27
With the rapid development of electronic technology and the ever-shortening lifecycle of electronic products, higher and higher requirements have been put forward for PCB Board assembly manufacturers. At the same time, global market competition has caused companies to face increasing international pressure. In order to survive and develop in the ever-changing market competition, modern PCB board assembly and manufacturing companies must adopt advanced production models to respond quickly to customer orders and provide high-quality, low-priced products. System integration and information integration (CIMS) are important technologies for improving enterprise management efficiency. Many companies have improved their level of production management and market competitiveness by continuously improving the automation of the placement line and introducing advanced enterprise-level management information systems (such as MRPII, ERP, etc.). However, general MRPII/ERP only manages enterprise-level resource plans. It can usually only process historical or forecast data, and cannot timely and accurately reflect the equipment status and production data of the current production site. At the same time, the on-site production equipment control system cannot transfer real-time production data to the upper-level resource management system. As a result, the enterprise resource planning layer lacks effective real-time information support for equipment, and the control link cannot be effectively optimized for scheduling and coordination [1]. Therefore, how to effectively combine the advanced production line control system with the enterprise-level production management information system and build a bridge between them to provide information communication is an urgent problem to be solved in the enterprise information construction. The Manufacturing Execution System (MES) solves this problem. The manufacturing execution system is a workshop-oriented management information system located between the upper level planning management system and the lower level production process control system [2]. It collects real-time data from the site to achieve optimal management of the entire production process from the order to the finished product. The PCB board assembly industry is a typical process manufacturing industry, and the equipment is highly automated. In order to fully tap the production potential of advanced equipment, optimize production behavior, and comprehensively improve the level of enterprise information management, the construction and application of MES is particularly important. This article is based on this idea, taking the dynamic quality control of the production process as the goal. According to the informationization status and characteristics of PCB board assembly companies, this paper proposes the construction and application of MES for PCB board assembly companies.

2 Status and Problems of Informatization in PCB Board Assembly Industry

The production and manufacturing departments of modern PCB board assembly companies use a large number of automation equipment such as screen printing machines, placement machines, and reflow ovens, and basically all use industrial computers for control. Because the vendor's data interface and format are different from each other, device information cannot be shared in a centralized manner, and many "information isolated islands" are formed, and unified data analysis and processing cannot be realized. Although most devices have the ability to collect production process parameters, there is no network connection between the devices. The acquisition parameters can only be completed by manually viewing the display or disk backup, and cannot timely respond to the operation of the entire production line, resulting in poor real-time performance. At the same time, manual collection increases workload, reduces work efficiency, and accuracy cannot be guaranteed.

The characteristics of the PCB board assembly industry determine that if there is a problem in one part, the entire batch of WIP will be scrapped. Therefore, it is necessary to monitor key production parameters in real time and sensitively and locate the wrong position, giving correct warning information. At the same time, some important parameters are automatically controlled and adjusted.

Businesses are no longer satisfied with the simplest and most direct kanban information and need to dynamically monitor production activities based on real-time production data. On this basis, supplemented by quality process control methodological methods, scientific and systematic quality process analysis is conducted to support the judgment and timely processing of on-site production processes to improve production quality.

There is a gap between the enterprise planning layer and the field device control (DCS), and a complete automatic/semi-automatic closed-loop business process cannot be achieved. As the PCB board assembly industry has the characteristics of small batch diversification and frequent changes of orders, production schedules and order requests cannot be timely delivered to on-site operations, and the workshop cannot timely adjust production schedules according to actual conditions. Reduce work efficiency, affect the delivery time. The stability of the delivery date is an important factor for the customer when purchasing.

In addition, there are a large number of repetitive operations and error-prone processes in the on-site production process. For example, how to effectively manage the use status of a large number of on-site mounting racks, how to ensure the correctness of the loading position, and how to verify the correct correspondence between the release work order and the production BOM.

The above issues are closely related to each other and affect each other, and their comprehensive consequences have seriously hampered the development of the company. In the increasingly fierce market competition environment, effective solutions will be of great significance to the PCB industry, and can obtain huge direct economic benefits.

3 Achieving Goals and Technical Routes

The main construction goals of MES for PCB board assembly industry are:
1) Build an MES command and dispatch platform based on unified basic data and a unified system framework. Provides flexible and customizable user interfaces, business modules, and secondary development interfaces.
2) Research and development of MES systems that target the lean production management model and aim at dynamic quality control of the production process. By establishing a management control model for the SMT assembly line production process. Realize the real-time collection, monitoring and scheduling of key processes and equipment production and quality data. Realize integrated information management from product production task assignment, equipment management and on-site dynamic dispatch.
3) Provide dynamic quality analysis means, real-time quality problem alarms, promote the improvement of management level, and gradually shift the quality management mode from manual inspection to automatic processing and real-time control. Establish a quality knowledge base to promote the optimization of quality standards. Through the cycle of collection, analysis, processing, and accumulation, continuous improvement of quality is achieved.
4) Complete integration with the company's existing information system.
According to the characteristics of the PCB board assembly industry, the functional module division of this program mainly includes data acquisition, monitoring and alarm, dynamic quality process control, process planning and scheduling, equipment management, and auxiliary production site management. The business relationship of each module is shown in the figure below:



MES module business diagram


3.1 Data Acquisition, Monitoring and Alarming

3.1.1 Main Content The SMT production line's automation equipment group is built into the industrial network and connected with the internal office LAN. The software and hardware communication modules are installed on the control computer of the production line automation equipment to automatically collect real-time production data and transmit data to the data through the network. Processing center. And the data processing center shared information transmitted to the monitoring terminal through the network.

3.1.2 Data Acquisition Subsystem The [Data Acquisition Subsystem" is used to collect real-time production information from the SMT workshop field automation equipment and transmit it to the monitor interface to be displayed in the form of interface required by the user. At the same time, according to the needs of users, the collected data is stored, output, and other secondary processing. Alarm information is output according to the alarm condition.
The "Data Acquisition Subsystem" considers integration with other DCS control systems in the SMT workshop. At present, most of the advanced equipments provide OPC/DDE interface. Therefore, in the data acquisition system, there should also be an interface program with OPC/DDE services to provide comprehensive read/write interactions so as to obtain instant production and quality information from the control system. .

3.1.3 Dynamic Quality Process Control
automatically import field data collection due to the large amount of data, the need for efficient and rapid means of analysis, quality analysis in real-time, control of the current production status. The Statistical Process Control module is to use statistical principles to collect and analyze quality inspection data, effectively control the production process, continuously improve the quality, reduce the defective product rate, and enhance the efficiency and competitiveness of the company.
The quality analysis content provided by SPC includes change analysis, stability analysis, effective capability analysis, variation factor analysis, and process correlation analysis. Corresponding to this, the program provides a total of 13 kinds of statistical charts for counting type and measurement type: X-MR chart, XR chart, XS chart, P chart, NP chart, U chart, C chart, running chart, histogram, defect arrangement chart. , Arrangements, scatter plots, and DPMO (defects per million) control chart analysis based on PCB board assembly industry characteristics.

Detailed scheduling and real-time adjustments to production planning and process planning and scheduling under 3.1.4
support in the field to collect data. ERP as the company's high-level planning and decision planning system, the development of the workshop's main production plan, accurate to the daily production plan. MES uses JIT (Just In Time) as the core of the plan implementation and control system at the grassroots level to refine the daily production plan. Read the main production plan information from the ERP, determine the objective function and constraint conditions according to the order type, production mode, etc., select the scheduling algorithm, establish the scheduling rules, generate a detailed production plan, and implement the production organization at the execution level. In order to achieve the real-time performance of SMT pipeline production scheduling, the scheduling algorithm requires high accuracy, short calculation cycle, and simple calculation process. The desired scheduling period is determined in minutes or the arrival of a new task (bottleneck). According to the actual situation of the enterprise production line and other human factors, such as flexible scheduling, manual adjustment methods, and emergency scheduling solutions. After the execution of the plan is completed, the data collection subsystem feeds back feedback to the ERP.

3.1.5 Device Management Device Management is responsible for managing
workshop SMT assembly line equipment information, it gets real-time operating information from the data acquisition system. Through the statistical analysis of these information, the utilization of the equipment is obtained. At the same time, the equipment information can be called by the process planning and dispatching system. The tasks of equipment management are mainly implemented by workshop equipment management departments and production departments. It mainly includes maintenance of basic information data, maintenance of business information data, and status information data. According to functional requirements, the equipment management module mainly includes the following parts: equipment file management, equipment change management, equipment inspection management, equipment maintenance management, equipment maintenance management, equipment lubrication management, equipment operation management, equipment status statistics and analysis, equipment inquiries, etc. .

3.1.6 Auxiliary production site management is used to simplify the on-site operation of the workshop and assist the daily management functions of the SMT production workshop. include:
1) Feed Management Module: Maintain the basics and usage information of the racks to improve the management efficiency of the racks. It is convenient to inquire information on the status, maintenance records, maintenance records, scrap records, and online details of all racks.
2) Reload comparison module: Compare the refueling of the production line, confirm whether it meets the requirements of the current station, and record the refueling behavior, which is conducive to the query of refueling information.
3) Work Order Comparison Module: Through the comparison of the production BOM data file and the work order file, the BOM material quantity is summarized, the difference information is found, and the correctness of the processing is ensured.
4) Mounter program verification and optimization module: Extract coordinate data from CAD system, generate corresponding patch files, correct program problems, optimize placement path, and ensure the correctness of placement.
5) ERP interface module: completes the common interface with the enterprise's existing ERP system, realizes data exchange and sharing with ERP software, dynamically inquires and displays production plan information, and promptly returns completion status.

3.2 Acquisition Drive Development

In order to optimize the configuration, enterprises generally come from multiple manufacturers when they build SMT production lines. At present, there are a wide variety of SMT production equipment on the market. Different equipments and even different models of the same equipment have different data interface modes. General data collection methods include: using industry-wide protocol acquisition, acquisition through a device-defined communication protocol, and acquisition through the device control system interface. In addition, you can also add a capture card to collect data. This section takes a typical SMT production line as an example to discuss the above several acquisition methods.

3.2.1 Screen Printer Data Acquisition Screen printing is the process of applying solder paste (or curing glue) onto a PCB board. DEK automatic screen printing machine as an example (such as: DEK265LT, DEK265HORIZON) to achieve data acquisition, acquisition parameters include: production models, production numbers, printing methods, squeegee pressure, squeegee speed, separation speed, cycle time, printing direction.
This module collects screen printing machine data through the industry common protocol. The DEK screen printer controls the device through the connection between the Machine PC and the Machine Controller. The Machine PC is an industrial control computer and uses the Intel Pentium series CPU to run the corresponding control and monitoring software on it. The Machine Controller implements specific device control and communicates with the Machine PC through the Next Move Card.
The control system of the screen printing machine is relatively simple compared with the placement machine and adopts the control of the main board. The DEK screen printer has a host communication function that conforms to the open standard GEM/SECS II. The GEM/SECS II agreement is an initiative drafted by the International Association for Semiconductor Equipment and Materials (SEMI) with the aim of harmonizing control systems and equipment from different vendors. The communication standard between the manufacturing equipment and the master computer is defined by the GEM/SECSII, SEMI E30, and E37 (HSMS) protocols [2]. Devices with GEM-compatible interfaces can be easily integrated into the enterprise's CIM policy. The GEM/SECS II (TCP/IP) host communication function facilitates integration of silk screen resources throughout the entire production line.
The SEMI-related protocol is used to write the communication driver to collect data responses between the driver and the device. At the same time, it is necessary to open the corresponding Host Comm switch to the Enabled state on the main screen of the screen printer. It is worth noting that the GEM communication board of the general screen printer is not configured by default and needs to be installed separately.

3.2.2 SMT data acquisition SMD is the process of attaching SMD devices to PCBs. It is a key process for SMT assembly lines. The placement machine has complex control parameters and high precision requirements. It is the focus of the program for collecting equipment objects. Take Matsushita Panasert (MSF, MV2VB, MSR), YAMAHA (YV88II, YV100II) placement machines as examples. The collected contents include production information, mounting information, nozzle information, feeder information, and program information. The key parameters are production number, downtime, working hours, work efficiency, number of picks, number of placements, and number of throws. According to different analysis conditions such as suction nozzle, rack, and time period, the adsorption rate, the mounting rate is too low, and the output of a certain model is reduced.
1) Through the device monitoring software interface to collect the patch device using DOS operating system (such as YAMAHA YV88II, YV100II) can communicate with the COM port of the mounter through the offline software, the acquisition driver obtains the corresponding acquisition directly from the process file generated by the offline software data.
Another method is to install a serial communication program on the device, communicate with the serial program on the collection server in the DOS state, and send the process data to the collection server for monitoring and storage. For example: YAMAHA SMT process data is a PDT format text file. The entire document is divided into three parts: HEAD, HEAD and COMP. After collecting the server, it can be directly decomposed by the format.
2) Collecting through the device's self-defined communication protocol Panasonic's Panasert SMT is a control system that uses the motherboard as its core and uses a card structure. Panasert placement machine uses P8000 control box, which is composed of HMI and MMC control modules. The Panasert placement machine provides a 25-pin RS232 serial port for host communication, which itself is used in the networking of information systems (such as Panacim's Pamacim, Unicam's Unicam, etc.).
Through the Matsushita Host Communication protocol, it provides a two-way response communication between the device and the host. The communication instructions include start and stop positions, length segments, and data segments. To implement data communication, it is necessary to set the placement machine to the Online state. The placement machine generally provides three working states: Auto, Semi, and Manual. The Online state can be set only in the Auto state, and Offline is automatically set in the other two states. Therefore, real-time acquisition of relevant data can only be achieved in the Auto state. However, it is not possible to perform Step and other debugging work in the Auto state. Therefore, the Auto state is used during production monitoring, and the semi or manual state is switched over during maintenance and inspection. The placement machine provides serial communication speed ranging from 4800 to 19200bps according to different models and user settings [3].

3.2.3 Reflow oven data acquisition The reflow soldering process warms the component board to melt the solder paste and achieve electrical connection between the device and the PCB board pad. Take the HELLER 1500W~1809W series as an example for reflow oven data acquisition. The collected data includes the furnace temperature (set value, actual value) and belt speed in each zone. At the same time, according to the time interval, the trend line graph of the furnace temperature is plotted to indicate that the furnace temperature is too high.
This module collects data through the device control system interface. HELLER reflow oven is controlled by PC. Its control mechanism includes ENCODER (decoder), KBLC card (speed control card), CONTROLLER card (main control card), and MOTOR (motor). The PC and the main control card communicate through the COM port, collect device information, and issue control commands. The entire control route is closed-loop control.
By analyzing the HELLER reflow oven control system, the Heller Comm OLE Control module provides the control and collection functions of the reflow oven in the form of COM controls. The acquisition answering program is installed on the reflow oven control computer, and the real-time data is transmitted through the non-blocking SOCK connection and the acquisition driver on the remote acquisition server. Through a multi-threaded approach, a collection server can simultaneously connect multiple reflow ovens for data acquisition.

4 Economic Indicators

According to the site implementation and application experience of a domestic company in the past two years, the implementation of this project can achieve the following economic goals:
1) Monitor the quality of the production process, complete the analysis and correct abnormalities in advance, reduce downtime, increase equipment utilization, and increase processing capacity by about 10% annually;
2) Monitor production progress, rationally arrange production plans, reduce the number of machine conversions and stop time, increase production, and increase processing capacity by about 10% annually;
3) Decrease the management fee by 5% every year. After the implementation of the project, the annual output value will increase by 15%, cost and cost savings will be 5%, and a total of 30% economic benefit will be generated each year.

5 Summary

1) At present, the MES system is still in the exploration stage in China. Truly mature and common products and successful implementation cases are few, and implementation of MES is not one-sided. When an enterprise implements MES, do not follow the MES system definition. Should be based on their actual situation, careful analysis and reasonable planning. For the PCB Assembly industry, assembly line equipment is highly automated. Implementation of MES can be used as a starting point for data acquisition and monitoring. On this basis, implementation of on-site data quality analysis, scheduling and other modules can be effective.

2) The MES system is a bridge of information communication between production activities and management activities, and serves as a link between the entire enterprise information integration system. The ERP system that breaks away from MES will not be able to quickly organize production according to market demand. Therefore, the MES system should handle the interface with the upper ERP system.

3) Agile production is the core of advanced manufacturing model. It is difficult for traditional MES solutions to meet this requirement. MES for agile manufacturing must have good integrability, configurability, and adaptability. Adaptability, Extensibility, and Reliability [4]. Therefore, many foreign organizations and research institutes have begun to study MES for agile manufacturing [5].