Step 2: Optimized Assembly by Virtual Control

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STEP 2: Optimized Assembly by Virtual Control

A key element in a total MES solution for the electronics manufacturing industry is complete process engineering control. Rather than a process-engineering-centric or machine-programming approach, a virtual control approach considers the complete assembly line configuration. Logical sequential steps that create an optimized and documented process reflect today’s full technology mix in modern EMS environments.

A complete MES solution will drive PCB assembly operations to higher profitability. Breakthroughs in process automation improve efficiency and quality. These avoid a process-engineering-centric or machine-programming basis, considering instead the complete assembly line configuration. This leads to improvements in the new product introduction (NPI) process; on reducing work in process; and increasing overall equipment effectiveness (OEE). As a result, engineering change order (ECO) management is eased and managed in a comprehensive and traceable format.

Manufacturing process definitions (MPDs) include clear, logical, and defined manufacturing process steps; balanced lines; grouped setups; optimized feeders; optimized SMT programs; stencil design; virtual sticky tape; automated optical and X-ray inspection (AOI/AXI) outputs; plated thru-hole (PTH) machine outputs; planning manual assembly; and complete process documentation.

For complete assembly-line process solutions based on engineering control, manufacturing managers create a virtual PCB assembly (PCBA) and then a virtual assembly line and defined processes with documentation and run-ready machine programs. This task can be completed through comprehensive software.

Figure 1. BOM-centric process control involves creating virtual assemblies and lines pre-production.

Enablers for this approach encompass lean data models, a bill-of-materials (BOM) focus, globally available component libraries, uniform parts generation, and interfacing to assembly and test machines through software. These elements must be based around modern architectures and data management. Using logical sequential steps to create a fully optimized and documented process takes into account today’s full technology mix for modern electronic manufacturing and assembly.

Virtual PCBAs

In a lean data structure, the BOM forms the nucleus of the product model. This reflects real-life manufacturing, where everything revolves around the BOM. Changes in BOM data should be propagated to all assembly process definitions automatically. Integrate process control software to third-party enterprise systems in use at the facility, since these depend on the BOM as the point of reference for engineering, scheduling, purchasing, and supply chain management.

Input wizards included in process-control software suites can read, neutralize, validate, and merge computer-aided design (CAD) and BOM data, eliminating crude mistakes at input. Software tools prevent common mismatch errors better than human operators, aligning fiducial settings, component rotations, units of measurement, part attributes, and customer part number (CPN) mapping to internal part number (IPN).

To create a virtual PCBA, process control software automates parts-number cross-referencing to detailed geometric data definitions used in programming all factory machine types. This allows instantaneous on-demand generation of all shape-based part data at the machine level, with orientation and supply forms.

Once you have machine-neutral, factory-level outline shapes, they can be translated into machine-specific data across the EMS facility. These can be based on whichever line is selected to run the product, including lines that may have mixed machine platforms or lines at other facilities. This step generates product portability between lines and sites.

The final element in constructing the virtual PCBA is to consider the full panelization, where multiple PCBAs and/or carrier rails can be developed quickly and easily, allowing the most ambitious panel formations. This involves taking the individual PCBA data set and creating multiples or incorporating it into a larger panel.

A Virtual Line with Programs

By defining each assembly machine and its configuration, you can create a virtual model of each line. Combining this virtual line configuration with the detail on the virtual PCBA opens up a variety of choices and optimization algorithms. Components can be optimized on feeders; machine placement order determined; operators can load-balance machines to remove idle time between serial machines or parallel process steps; and hand-assembly balancing and optimization can be performed.

Another tool, virtual sticky tape, simulates placement of components on the PCB to visualize machine-based programming. Virtual sticky tape allows the engineer to work off-line, resolving programming issues, such as component offsets, component orientation, and machine-based component shape management prior to actually building a board. Through these various virtual stages enabled by modern software, engineers create machine-ready programs to suit the line configuration defined.

With machine and line configuration options and preferences laid out, process control software can provide an estimate on production timing. This allows a more accurate cost structure to be calculated for the product, thus helping provide more accurate manufacturing costs and quotes for new business development.

Define the Process

With the product and line settled, the final pre-production stage creates all necessary machine-operating programs and operator-level support documentation for the complete assembly line - pin in hole (PIH), SMT, and manual work cells. These MPDs are matched to work centers and resources defined in the virtual line and to the product model; they can hold user-defined information for inspection-and-test stages.

Figure 2. Process control software can balance assembly lines, optimizing production runs.*

In a low-volume/high-mix environment, this MPD need not be made as hard copy and manually placed at the work center. Drive document viewers or displays for each area; the whole assembly line can be driven from a single point on an appropriately networked system.

In a complete process-control solution, any change to the bare board design is propagated to all referenced projects, ensuring the change only needs to occur once. This is made possible by the linking power of a relational database that relates valuable information from one project to another, increasing production quality. A single point of change promotes fast handling of production variations and higher quality.

Production

Following this logical stepwise process eliminates errors in NPI and ECO processes. A BOM-centric model ensures that operators don’t have to perform the same task twice, whether it’s setting the polarization of a part, fiducial definition, or CAD import parameters. Time and quality metrics benefit from making changes only once. Improved variation handling also occurs when the same board data merges into many projects, each with different variations. Any changes made to the board will propagate to all referenced projects via software controls. This reduces the risk of error and makes comparison reporting easier, raising quality. If an ECO requires a new part, factory-wide process control software can immediately generate updated machine data and programs for all machines on all lines, so any ECO can be implemented quickly, without tedious and error-prone manual entry, or tweaking machine data by measuring physical parts with calipers or by searching for datasheets on the Internet. Accelerated NPI process is attainable.

With proper process control, on-line machine-data debugging is eliminated, replacing downtime with production. Well-defined part data will be ready to run on any relevant machine on the line, improving line balancing - reducing WIP. Virtual lines allow accelerated setups and fewer line-side trials, with virtual sticky tape leading to higher OEE.

Accurate centralized part data makes it easier to decide where to assemble a given product, or even to move a product to another line if a hot job needs immediate attention. The result is factory-wide balancing - program portability - or better factory selection. Ultimately, this can reduce total cost of ownership (TCO) for products.

Traditionally, assembly factories have separate machine libraries for each machine. These libraries usually contain thousands of shapes, many of which are duplicate, defined by different operators at different quality levels. The top-down factory-wide approach ensures that the assembly floor will have only the shapes it needs, defined once and at the highest quality level. This eliminates problems usually associated with manual generation of machine data, giving repeatability from machine to machine but also product to product, and beyond. Having parts data created by software means that it can be called up on demand, when you need it. The data is consistent, accurate, and readily available. No need to tweak and re-tweak data, which in time leads to errors in the library.

Conclusion

Improving the change control and traceability is a corner stone for product quality. Virtually modelling manufacturing lines gives the opportunity to balance and optimize between and on each machine. It reduces many of the seven wastes of lean. Virtual sticky tape contributes to the battle to acheive zero defects. Process control software’s capability to work through large varieties of data files and input types - quickly producing reports, options, and recommendations - enables improved internal and external communications, due to more accurate information made available earlier in development.

* Image based on vPlan software diagrams

John Paschke, manufacturing productivity consultant, may be contacted at Valor Computerized Systems, Yavne, Israel; www.valor.com.