Information Management Gaps for Board Fabrication and Assembly Print E-mail
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Written by Eric Simmon   
Thursday, 03 September 2009 17:42
  

Progress toward complete data packages has been slow.

Within board fabrication and assembly, there are several areas where improvements in information management are needed. The link between design and manufacturing, part traceability, and PWB systems all have new needs that can be addressed by improved information management systems.

There has been little progress in the transfer and communication between CAD and CAM systems. The problems fall into two main categories: incomplete information and non-intelligent data. Even today, most jobs coming into a fabricator or assembler contain incorrect or incomplete information. This may be in the form of missing data, an incomplete package description, the wrong data, or other inconsistencies within the data file. This lack of information greatly impacts cycle time and increases the chance for error. Intelligent data would further aid the transfer of information. Intelligent data uses complex data structures that associate attributes and even behaviors as one. This type of data would flow more easily through the data systems and improve interoperability.

Working with CAM tool suppliers, the industry has developed a diverse set of tools to automatically input a wide variety of formats, including automatic interpretation of aperture slits and tools to put some intelligence back into the data. However, this development seems redundant, as the design system already contains this information. Instead, a way of transferring this intelligent data is critical to the industry’s success.

Education about, and standardization of, the type and structure of information required for a complete printed board design package is necessary to eliminate the data transfer problem. This also includes standardization of component information for printed board assembly. Such standards have been developed and continually upgraded for years; however, progress toward more intelligent data exchange has been minimal. Non-intelligent Gerber data1 remains the most common data transfer format. This format is error-prone due to issues with entering and interpreting aperture lists. Unfortunately, the industry has tried to push the Gerber machine language beyond what it was originally intended to convey. Part of the problem is the competitive nature of tool providers and their unwillingness to cooperate on a standard format. As long as this situation exists, it may be difficult to achieve highly organized, intelligent data transfer shown in Figure 1.

Figure 1

NIST’s 2004 report, Economic Impact of Inadequate Infrastructure for Supply Chain Integration,2 estimated the lack of integrated IT systems cost the electronics industry supply chain nearly $3.9 billion per year. As most board fabrication is outsourced, the problem has been exacerbated in recent years.
With the rapid changes in component packages, many new orders are, in reality, new assemblies and new board designs. Because a large portion of the design changes with every order, traceability and configuration management have become important issues.

CAD/CAM needs. CAM continues to mature despite the issues between CAD and CAM systems. Many CAM suppliers have focused on providing automatic input of the wide variety of data formats, adding intelligence into Gerber data received, analyzing the data for manufacturability and, most recently, semiautomatic and automatic data editing. This focus has been driven by board manufacturers’ increased demands for faster tooling cycle time and better quality. More intelligent data transfer will enhance manufacturability.

The case also has been made for integrating the many steps in the preproduction process. This would have the dual effect of streamlining the process and decreasing the product time-to-market. It also would improve the overall design quality by providing feedback during new product introduction. Early fabrication involvement, clear communication of requirements, and maintaining the original design intent all would be byproducts of this integration. This process also would facilitate the engineering of new designs and reduce the number of times the design would have to be reengineered.

The 2009 iNEMI Roadmap3 identifies several PWB fabrication needs, including:

  • More communication from CAD systems to CAM systems for fabrication (early manufacturing involvement, documentation, procedures, etc.).
  • More intelligent, bidirectional, data transfer standards from CAD to CAM, containing information on physical boards (photoplot, legend stencil, solder mask, drill, materials, etc.), electrical (netlist, impedance, component designators, etc.), and component descriptions.
  • A common data format to support data transfer between CAD and PWB CAM systems.

Traceability and issue resolution. Within a company’s factory network, an immediate understanding of a single product’s location is highly desirable to provide the most efficient and effective response possible to changing product demands. By creating a closed-loop system, information from the factory floor can be used as feedback, not only for the process control systems, but also for the product information systems. Wafer-level tracking is now available in fabs, while lot-level tracking has been common since the 1990s. In assembly and testing facilities, an individual unit is now traceable as it traverses the production line. A unit can be assigned a unique identifier that can be tracked through the production cycle. This makes product management at the lot and unit level feasible and beneficial. When coupled with a precise understanding of equipment fungibility, utilization and availability, unit tracking becomes a major advantage to the companies in the supply chain and, ultimately, to the end-customer.

In situations in which excursionary materials are identified “after the fact” and containment and disposition become important, use of material tracking in concert with corporate databases allows a rapid understanding of the location of “at risk” material and enables rapid response (Figure 1). Further, using this information to understand manufacturing cycle times, precise product volumes and unit location in the assembly line allows better optimization of production to meet demand. It also opens possibilities for starting new product manufacturing with minimal impact to existing production.

Another aspect of product traceability is to improve adherence to environmental requirements (both regulatory and business requirements) and aid in the identification of counterfeit parts. The unique ID can associate the unit with specific information related to the unit, such as material content data and manufacturing energy usage. By tracking the unit through the supply chain, a stakeholder can gain confidence that the unit traveled through authorized sources and is an authentic part.

The desire to collect traceability data highlights the need for factory information systems capable of collecting data from floor equipment in real time. In the past, assembly lines could be run somewhat open loop because the need to monitor every action was not necessary to produce product. However, collecting genealogy data for every product requires near-continuous communication between the machines assembling the product and the information management systems that pass those data through the supply chain. As a result, manufacturers are investigating methods for establishing communication between their applications and machines. Further infrastructure development to support the required traceability is needed.

Assembly information management. During the mid ’80s to mid ’90s, significant changes took place as the industry moved from through-hole to surface-mount technology. Over the past 10 years, innovation of assembly techniques has been relatively stagnant, as products commoditized and margins reduced. Manufacturers are reluctant to invest in holistic strategies for factory information systems. Although a long-term information management strategy will most likely save money, companies are investing in short-term solutions that may be suboptimal in the long term, but are perceived to have better cost-benefit ratios in the near term.

Large boards are usually assembled one at a time; however, smaller boards typically are laid out in a smaller panel (subpanel) in an array format. This array optimizes the assembly process. To obtain multiple panel images usually involves modifying the data machine language Gerber files or other drawing files for the fabricator. Two industry formats can improve this situation. One standard is hierarchal, looking through all the layers of the electronic assembly (IPC-25114); the other is layered similar to Gerber machine data, however, with intelligent descriptions (IPC-25815 and AP2106). Both formats are able to describe the board to panel or pallet relationship.

Unfortunately, this information usually is not provided to the board manufacturer. Historically, engineering and purchasing departments have not been inclined to work with the supplier to obtain the highest added value. Customers typically feel the challenge of making panels cost-effective rests solely with the supplier. This is a fallacy that needs to be corrected to establish some form of “cost of ownership” style of service for the end-user and supplier. In some instances, a specification is developed to capture the panelization strategy for board fabrication, as well as the assembly panel array (pallet). The details of the specification, however, must be flexible enough to allow choices by the fabricator in terms of optimum panel sizes. This is a cost driver and it impacts yield calculations and resulting profits.

In addition, in-depth discussions must take place with the assembly resources, as they are the users of the panel and have to deal with the breakaway methodology, testing demands and optimum throughput size for their process. Whether scoring, routing (leaving tabs) or a combination, the depanelization strategy should always be reviewed with the supplier during fabrication and assembly. Figure 2 shows the movement from fabricator to assembler, plus the data and naming descriptions that accompany those transfers.

Figure 2

Existing standard information models cover the board, assembly, the fabrication panel, the assembly array panel, all fixtures (electrical bare board test, in-circuit test, assembly, etc.), and the electrical test vectors. The solder stencil can be extracted from files based on these models. Presently, however, it is generated from the machine language Gerber data. Stencil openings are then modified to provide the optimum amount of solder paste to maximize the solder joint quality, and component placement data must be loaded separately into the placement equipment. Because of different design software packages with no common output format, there is no direct input of data into the placement equipment. There is also diversity in the way the designs are described, such as differences in the way the 0,0 reference point is defined and communicated to the assembler, no orientation or physical size of the component provided, differences in the parts nomenclature, and different types of bill of materials.

Printed board assembly needs include:

  • The ability to transfer data from the design system to the assembly equipment via some format with more intelligence that will support the development of test data, automatic generation of component placement data, and data for failure analysis of defects.
  • Consistent naming conventions for all component types (common component libraries), such as those defining component type, length, width, height, centroid data, etc.
  • Sophisticated design rule checking in the CAM environment.
  • Design tools that implement manufacturing rules, similar to those used in the semiconductor industry where process rules drive design methodologies.
  • New test strategies, utilizing intelligent data from the CAD system.
  • A common data format to support data transfer between CAD and assembly CAM systems.

Conclusion

Improving standards for design and manufacturing data, and implementing these standards consistently in information management systems and manufacturing equipment, will enable higher productivity and low costs.

The Information Management Systems chapter of the 2009 iNEMI Roadmap provides a more complete summarization of the gaps/issues faced (inemi.org/cms/
roadmapping/2009_roadmap.html). 

References

  1. Barco Graphics, “Gerber RS-274X Format User’s Guide,” 1998.
  2. NIST, “Planning Report 04-2, Economic Impact of Inadequate Infrastructure
    for Supply Chain Integration,” June 2004, nist.gov/director/prog-ofc/report04-2.pdf.
  3. iNEMI, 2009 iNEMI Roadmap, April 2009.
  4. IPC-2511B, “Generic Requirements for Implementation of Product Manufacturing Description Data and Transfer XML Schema Methodology,” January 2002.
  5. IPC-2581, “Generic Requirements for Printed Board Assembly Products Manufacturing Description Data and Transfer Methodology,” May 2007.
  6. AP 210, “Standard for Electronic Assembly Interconnect and Packaging Design,” (ISO 10303), April 1999.

Eric Simmon is an electrical engineer in the Electronics and Electrical Engineering Laboratory of NIST’s Electronic Information Group, Semiconductor Division; This e-mail address is being protected from spambots. You need JavaScript enabled to view it . He chaired the Information Management Systems chapter of the 2009 iNEMI Roadmap.

Last Updated on Wednesday, 09 September 2009 18:44
 

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