Dramatic enhancements in IC functionality over the past decade have brought tremendous advantages to PCB designers. Today's denser, faster devices pack multiple high-performance functions into smaller and smaller footprints. But these same revolutionary advances have brought to the forefront an increasingly challenging issue for board designers. Rapid advances in IC fabrication technology coupled with lightning-fast production cycles and shrinking time-to-market windows have conspired to speed up product obsolescence.
Engineers building cutting-edge functionality into their board should not expect their designs to remain static for long. By some estimates the average component life cycle has been cut in half, from seven to 10 years in the early 1990s to as little as two to five years today. In some highly competitive markets such as wireless handsets, where constant innovation drives market success, today's high-performance chips can be rendered obsolete virtually overnight.
For PCB designers, these shrinking component life cycles present an unending challenge. Designs based on components available just a few years ago can easily be rendered obsolete. And keeping abreast of the life cycle status of thousands of parts from hundreds of suppliers can pose a formidable task.
How does the purchasing department at a board manufacturer keep its designers up-to-date and informed of the latest changes on the status of hundreds, if not thousands, of parts? What is the most effective way for information to flow from the supply chain to the enterprise business system? How can a designer quickly determine what kind of impact a phased-out part will have on his board design? How can he or she ascertain exactly what impact a new replacement part, or even the same part from a different manufacturer, will have on board parasitics, signal integrity and EMI? And how should information flow when a parts change dictates a redesign or rework of a board?
The first step toward eliminating many of the traditional pitfalls inherent in parts obsolescence is breaking down the barriers to communication between design team members. Today's increasingly complex electronic products demand the skills of a wide variety of personnel-from designers of systems, boards and components to procurement, manufacturing and test experts.
The key to managing ongoing component obsolescence is the development of a design environment capable of enabling seamless and automatic communication across these multifunctional teams. By sharing design data across the entire enterprise, product development teams can most efficiently migrate from outdated to next-generation parts in a cost-effective and timely manner.
To achieve this goal, however, this free flow of information must become an integral feature of a manufacturer's product development environment. Parts obsolescence is a commonplace fact of life in electronic system design today. Information on parts availability and status is constantly changing. Vendors notify their customers on a continual basis of parts that are nearing the end of their life. Often these notices include important data on the source and availability of replacement components.
Accordingly, it is crucial that the enterprise information system and the engineers who use it retain a tight connection to the supply chain. Whether suppliers notify their customers by hard copy or electronically, this parts change information must be input into the enterprise business system on a timely basis. Engineering change orders (ECOs) and parts data must be continually exchanged and managed among product data management (PDM), manufacturing resource planning (MRP) and enterprise resource planning (ERP) systems. If this supply chain data is not accurately reflected in the various enterprise business systems, designers resurrecting an older design or merely updating an established one likely will pay a severe price in additional board iterations and higher overall product development costs.
While individual so-called "point" EDA tools do little to close this communication gap, some of the newer PCB design environments provide a solid foundation for timely and automatic communication between the enterprise business system and the supply chain. To ensure component data is up-to-date and accurate, some of the newest board design tool environments, for instance, add interfaces from their integrated front-end design tool sets to popular PDM systems. These tools enable the engineer to generate a bill of materials (BOM), input it into existing component inventories and verify it for completeness and accuracy. This capability allows the designer to distribute design data to others in the enterprise, particularly in procurement and manufacturing, and helps guarantee that the engineer has the latest information on parts approval and availability.
Tight communication between the enterprise system and supply chain allows a design engineer using the company component database to be automatically notified of a part's change in status. Typically the designer revives an established design by resurrecting the original schematic and identifying which parts will be used. Those parts are usually selected from a corporate-approved parts list.
Today's design engineer can use a component search-and-selection tool to quickly search corporate parts databases to locate parts. This tool is used to verify the integrity of the entire design by ensuring that the information on the schematic is consistent with the corporate database. Once the desired part is found, the engineer drags and drops the component into the schematic. At the design verification stage, the design information is compared to the corporate database. If purchasing has indicated that a part in the database is about to become obsolete, it is flagged. At this point the designer immediately learns which parts in the design must be replaced.
This capability plays an important role in large, geographically dispersed organizations where communication between different design groups or between purchasing and design often can be delayed or nonexistent. Often in a large corporation, multiple design groups access data from a single, distributed database. By linking the enterprise business system with the supply chain, information from the purchasing department on the latest status of obsolete parts can be passed easily to multiple design groups across the organization. The availability of this information early in the development cycle before the board goes to manufacturing will result in substantial savings by way of shorter development cycles and fewer respins of a design.
Locating replacement parts
Once the designer has identified which part or parts in the design are obsolete, the next step in the process is to find a suitable replacement part. In some cases, the purchasing department might already know, from information provided by the supplier, who the second-source suppliers are, or which replacement parts are appropriate for a particular application. In those cases, the replacement part can be identified in the part change notification procedure and its data integrated into the design for verification.
But many times, replacement part data is not immediately available and the design engineer ends up with the responsibility for researching and locating a suitable replacement device. This can be a time-consuming task. By some estimates as much as 30% of a designer's time is spent researching and selecting parts for a design and finding replacement parts. Moreover, the symbol generation process that follows is also time-consuming and tedious.
During the past five years, the rapid evolution of online services has significantly eased this task. Engineering and purchasing personnel can now search for key components worldwide via the Web. But the key to maximizing the efficiency of that search is having the right parts creation and management tools at your disposal.
The search for component information on the Web is particularly ripe for automation. Some online services now provide vast component databases where an engineer can quickly search for hard-to-find components and acquire key component specifications. One such service is available through PartMiner's online database of component information on its Free Trade Zone Web site [www.partminer.com].
Using this service, a designer can search for parts based on device category, a manufacturer's parts number or electrical parameters. A designer searching for static RAM, for instance, can specify the preferred organization, access time and package. The service then narrows the search to find the components meeting those specific criteria. The designer then can view the datasheets of those components to identify the best part for a specific application.
Once the replacement component is selected, however, the job is only half done. The next crucial and often time-consuming step is to create a part symbol that can be placed in a schematic. Typically this task has been performed manually in a tedious, error-prone and inefficient process. Some of the tool suites today can dramatically improve a designer's efficiency and reduce the potential for error by automating this function.
One tool, for example, automatically connects to PartMiner's Free Trade Zone. Once the designer selects a component, the tool automatically generates a symbol and populates a database with parametric data. The symbol can be immediately placed in a schematic. But the process also gives designers sufficient capability to modify and control how the symbol is created. Designers can specify parameters such as pin spacing, pin length, text height, grid spacing and pin location during the symbol generation process, or embed specific graphics to conform to company standards. They also can add corporate information such as a part number or PCB footprint to comply with requirements for reports on a PCB net list or BOMs.
Obviously, it is also crucial that the entire symbol generation procedure interface seamlessly with the library management system that manages the parts database. That way, the symbol librarian can be notified automatically when a new parts request is pending. This enables the librarian to easily modify the part, add company-specific data and move the part to the release library once it has been approved.
Maintaining constant communication between purchasing and design is critical throughout this process. One of the advantages of a comprehensive environment is the ability it gives purchasing to track the progress of component selection by the design engineer. Through the BOM upload, purchasing can learn which replacement part the design engineer has selected. The purchasing department can then investigate whether the device in question is available in sufficient volume and, if it is not, tell engineering to select an alternate device. This, in turn, can minimize redesign efforts made with unavailable parts and help accelerate the redesign process.
The next step in the process is to analyze the impact of the new part or parts on the existing design. This is especially crucial today. Rapid advances in IC fab technology have allowed component manufacturers to build replacement ICs that can offer the same functionality as their predecessors, but with a significant impact on system reliability that is often difficult to discern. Newer devices running at higher clock frequencies and featuring shorter signal edge rates can create signal integrity problems that are difficult to resolve without returning the board to layout.
Transmission line effects can quickly lead to such problems as ringing, overshoot and undershoot and threaten noise margins and monotonicity. Sub-nanosecond edges can create high-frequency harmonics that can quickly couple into an adjacent interconnect and cause crosstalk. The substitution of faster parts also can lead to race conditions, in which a synchronous input data hold timing spec is no longer met. And faster signals are more likely to produce radiation, bringing up EMI as yet another design consideration.
Clearly PCBs repopulated with the latest-generation ICs must be carefully analyzed for these effects. Even when the design engineer finds a verified part on the corporate database to replace an obsolete device, he or she must retain a high degree of skepticism about its ability to run in an established design.
Ideally, the board design with the updated components should be run through a high-speed transmission line analysis tool to locate potential signal integrity problems before the board goes to manufacturing. Timing analysis tools can quickly identify potential problems that might lead to clock skew or race conditions. Similarly, analog and mixed-signal simulation tools, if appropriate, can verify the functionality of a design.
Moreover, if the board was originally designed to a predefined set of constraints, the new design should be tested against those constraints. By defining these issues early in the redesign process prior to manufacturing, designers can minimize the time and resources spent rectifying these problems, and avoid unnecessary respins of the design.
When these analysis tools are packaged into a single integrated environment, the process becomes much easier. Extensive design analysis capabilities can include signal integrity analysis, analog simulation and gate-level digital simulation. Once replacement components are integrated into an existing design, the design engineer can use a prototyping environment for the development of critical signal constraints, to test whether the original design constraints needed to be adjusted.
After the board layout is modified to meet those new constraints, the design team can run analysis and feed the results into a built-in spreadsheet-based constraint management system, and measure them against the predefined limits. Designers can add such physical constraints as component placement, net length and net separation for each object in a design. They can also add design-level constraints such as PCB stackup and test all physical constraints against the electrical analysis to ensure the design will function as planned. If the constraints are not violated, the board can then proceed to manufacturing.
If designers want to test the signal integrity of the connections between critical components, some prototyping applications allow them to analyze variations in net length based on component placement or variations in net routing topologies and determine the optimum result. Using a general purpose net topology editor, designers can extract net topologies from an imported PCB schematic and model trace parameters.
Once the design has been fully analyzed and is ready to go to manufacturing, the final step in the parts obsolescence management process is to ensure that all enterprise data systems are accurately updated. Ideally, the design tool environment will automatically manage all ECOs and track their progress through the organization. Any violations in accepted corporate procedure should be flagged.
Escalating time-to-market and cost pressures are no longer limited to new board designs. They play an equally important role in the replacement of obsolete parts and the constant renewal of established designs. Fortunately, the new comprehensive development environments with integrated obsolescence management capabilities can help designers cope with this ongoing problem.
By focusing on team collaboration, and ensuring timely and accurate communication across the entire enterprise, board designers can minimize the impact of parts obsolescence and ensure that their boards are updated quickly and in the most cost-effective manner possible.
Fred Saal is chief scientist at Innoveda Inc. He founded Quad Design Technology and held engineering management positions at Vitesse Electronics and Hughes Aircraft Co.
John Dube is engineering manager at Innoveda Inc. He spent 10 years with Viewlogic working on simulation libraries, programmable logic design tools and design collaboration technology.
© 2001 CMP Media LLC.
9/1/01, Issue # 1809, page 22.
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