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Managing the Engineering Process for Increased Profitability
December 31, 1969 |Estimated reading time: 7 minutes
Implementing a manufacturing process preparation system (MPPS) should result in improved process efficiency, lower overhead, reduced costs, increased quality and customer satisfaction, and increased profitability. Choosing the right MPPS therefore is crucial to business success and long-term growth.
By Jay Gorajia
The ideal MPPS must have the ability to support the full assembly engineering process, from design to volume production. Key elements of such a system include open architecture; ability to accept multiple inputs (e.g., bill of materials [BOM] and CAD data); reporting and documentation; manufacturing process simulation (MPS) for DFX; outputs for fixture/stencil generation; and assembly equipment programming and optimization (Figure 1).
Figure 1. Integrated approach to streamlined pre-production engineering.
Enabling collaboration between departments within a factory is key to decreasing overhead and streamlining the engineering process, thus eliminating process bottlenecks, human error and redundant work. When data is centralized and stored as an intelligent format, it is easy to import to enterprise resource planning (ERP) and manufacturing resource planning (MRP) systems for use in purchasing and planning, as well as manufacturing or product engineering departments. The factory can access the data through a well-designed network or PDM software, where the engineering and logistical data can be easily imported to various hardware vendors' software. The network also can streamline the data and knowledge transfer of the design to various departments (Figure 2).
Figure 2. Fully integrated CAD-to-machine engineering process flow.
Indeed, many assembly manufacturers want to streamline operations by using one integrated system for all engineering functions. For example, manufacturing/product engineers want to quickly run DFX analysis and simulation technology to evaluate manufacturability of the new design, identify any possible process bottlenecks or design issues that may impact yield and rework capabilities at the production floor, and generate not only optimized programs to reduce production time for an assembly, but use the same system to automatically and accurately generate documentation, reducing errors and rework. Most manufacturers currently have "point solutions" to attempt to solve different process bottlenecks or specific required functionality. This results in relying on multiple vendors, as well as interfacing issues resulting in data consistency problems, outdated software in the factory, non-scalable software packages forcing reinvestment in new software, retraining engineers while having to employ engineers who know these various tools, and increasing cost of maintenance for each vendor every year.
In addition, contract manufacturers benefit from standardization or normalization of BOM data, since their customers supply various different BOM formats and most ERP/MRP systems are much more limited in their ability to import such unstructured, inconsistent data sets.
CAD/CAM/CPL Conversion
Automating importation of various EDA/CAD systems and support for low-level CAM formats such as Gerber, IPC-D-356 and Excellon Drill is essential to the easy processing of required design data. In addition to these formats, the system must have a template-based interface to "teach" the system how to read virtually any format of component placement list (CPL). With this data set, the system can merge the information of the CPL, EDA/CAD data and Gerber/Excellon to one database, enabling a virtual simulation of the board.
BOM/AVL/AML Management
The ability to automatically import, clean and organize BOM files from new products is essential for an MPPS. A powerful, template-based BOM management module using a spreadsheet-like graphical user interface (GUI) is required to handle the almost infinite possibilities of BOM files provided by design centers. Most "point solutions" have a fixed set of BOM templates that cannot be modified or enhanced. Some accept only one to two fixed formats, and the user must manually edit the incoming BOM before importing into any assembly CAM system. The system should have a BOM management module that provides flexibility in handling various input formats and allows the user to edit the templates or create new ones for new customers.
Manufacturing Engineering
At this stage, a manufacturing/product engineer should review the data set, define the routing of the assembly through the factory floor, make decisions as to what processes and chemical types to use, attempt to identify any process bottlenecks, and evaluate cost/yield factors that may affect production of an assembly.
Figure 3. Checklist-driven DFX analysis.
The MPPS must facilitate these actions required. A comprehensive DFX gives the manufacturing engineers a virtual simulation of the board to automatically identify problematic areas, process bottlenecks and opportunities for yield improvements (Figure 3).
A typical range of DFM analyses that can be carried out at this stage includes:
- Verification of footprint pads, soldermask and solder paste relative to component pins and soldering constraints
- Analysis of placement fiducial targets relative to components, adjacent features and soldermask openings
- Analysis of test point densities and proximity of test points to components (for access)
- Stencil design for optimum paste volume and coverage, without fearing the effects of problems such as tombstoning or bridges, which would be a serious process bottleneck and affect yields significantly
- Verifying that pin contact areas, component pitch, number and type of pins, and how they relate to the footprint is vital to verify time delays and rework to avoid downstream problems.
Assembly Management
Several key aspects to line engineering and component assembly management lie within the MPPS. These include:
- Comprehensive tools for assignment of components to the pertinent processes and machines using rules-based methods
- A sophisticated algorithm for line balancing and optimization, based on both sequence and component feeder setup, reducing production time on the assembly line
- Creation of a single, centralized parts library, even for mixed-vendor assembly lines
- The ability to easily and effectively manage technical parameters such as CAD-to-NC component rotation values and component offsets to yield the highest throughput while maintaining the yield requirements.
Defects per million opportunities (DPMO), which is equal to (defects/opportunity) × 106 may be used for decisions based on statistical data. This will provide the engineer with the limitations of the machines and processes, using historical data.
Although many "point solutions" exist in this arena, a true MPPS should use the same consistent data set used in the BOM management, DFX analysis, stencil design and all throughout the engineering process to minimize errors and ensure no data loss or redundant engineering work, especially with regard to engineering changes required by the design centers. Support for mixed-vendor lines is crucial for real-line simulation and optimum throughput results. Only if the system can simulate a line, and have the true kinematics of each of the machines modeled in the software, will a real increase in throughput be realized. The simulation should be able to be accomplished off-line, so that production work is not interrupted throughout the optimization process. Output to various testing equipment, including AOI, X-ray and in-circuit test (ICT) machines should be supported.
Documentation Generation
Assembly and inspection documentations (SOP) are used for instructing factory floor operators. The MPPS must be able to automatically generate and provide feeder setup information, inspection station instructions and details on component preparation, based on the same central data used throughout the engineering process. The entire process flow should be represented in a single document, eliminating the need to manage scattered pieces of documentation.
Product and set up information with full intelligence should be available to the operator via documentation viewers for a paperless factory environment. These viewers should include component searching, part information viewing and color coding. Color-coded pages of the document also should be available in printable form for non-paperless environments (Figure 4).
Figure 4. Factory floor documentation automatically generated from centralized ODB++ database.
Small- and medium-sized assembly manufacturers may think that an MPPS is only for larger manufacturers. However, a key aspect of an MES is its scalability. Choosing low-end point solutions may serve the organization in the short term, but might mean extra cost, process inefficiencies and waste of current investments in the mid- to long-term, as more investment will be needed to purchase additional, more modern tools as the factory grows. A solution is for small- to medium-sized manufacturers to start with a smaller configuration of the MPPS, and then add more capabilities as necessary.
Conclusion
MPPSs directly improve profitability by freeing the time of production equipment on the factory floor, as well as reducing use of personnel. Increasing the speed of new product introductions, process engineering and engineering change implementation frees time for manufacturing and process engineering, which can be used to process and produce more assemblies and increase revenues without a corresponding increase in staff or investment in more equipment. The ability to build more assemblies with the same number of machines, respond to quotation requests faster, create higher-quality documents while reducing the chances of errors, and use more accurate BOM management functionality will reduce rework potential and increase yields, positively affecting profitability.
Jay Gorajia, executive vice president, may be contacted at Valor Far East, +852 2721 6619; Web site: http://www.valor.com