Component and design considerations for extended product lifecycles
A major consideration for components and an overall systems design approach is obsolescence, which in the materials and dimensions of a component can have a dramatic influence on the long-term viability of a product life cycle.
By Jack Bogdanski and Jeff Lamparter
A major consideration for components and an overall systems design approach is obsolescence, which in the materials and dimensions of a component can have a dramatic influence on the long-term viability of a product life cycle. Both are critical in the design and development of products for the defense and aerospace industries where communications, aircraft, navigation, guidance, and radar systems require long-term reliability and upgradeability.
Embedded electronics in applications such as missiles, ordnance, and aircraft continue to require increased processing and performance power without an increase in electronic component volume. Technology creators use a variety of obsolescence-management techniques that can be categorized in one of two ways:
- production engineering-based techniques, which attempt to control an existing situation; or
- design-based techniques, which attempt to minimize the initial problem.
Both of these techniques have potential disadvantages, whether it is the potentially prohibitive cost of finding component end-of-life (EOL) buys or the possibility of introducing unforeseen problems with more up-to-date products. Based on the circumstances of a particular program or product application, it is possible to combine these techniques to achieve the optimum results.
Circuit board designers in the defense industry must combine these techniques into an integrated approach to meet challenges of extended product life cycles, such as pre-planned product improvements, modernization, technology refresh, and operational system development.
These designers could use production engineering-based techniques for the first development phase, finding EOL buys, while at the same time employing design-based techniques, then planning for technology insertion system enhancements later in the product lifecycle. This is a good compromise for many applications, providing the benefits of the two techniques while minimizing the problems associated with each of them.
Each generation of application also changes the dynamics in component selection, as the next generation usually requires greater capacity and performance in the same or smaller footprint. A good example is the next generation of the small-diameter bomb (SDB2). Since the design and production of the first generation SDB, requirements have emerged for the bomb to be able to track and hit moving targets like enemy trucks. To enable an SDB to target moving objects requires sophisticated electronics that do not add space or weight. This is a design scenario for using field-programmable gate arrays (FPGAs) due to their reprogrammability capabilities as well as their inherent obsolescence and upgradeability. It is common for FPGAs to be used in products for 15 years and more.
Reducing the size of digital packages in systems is challenging, especially where processing performance to board space requirements are constrained by system architecture. Components such as multichip memory devices can help determine if a system has to be redesigned or can adapt to changing requirements. A well-designed multichip package addresses component and design considerations as it relates to obsolescence management. To support multichip module designs, FPGA manufacturers such as Altera proactively work with military and aerospace customers to supply FPGA die when size and space restrictions are critical. In addition, device, package, and speed grade derivatives are eliminated when die can be provided, thus further reducing obsolescence challenges.
One case study that illustrates this solution involves a design challenge for an application-specific board layout. The designer had a board area of about 25 square inches. With much of the board area populated by the necessary support circuitry such as passives, connectors, and power supply devices, the approximate space remaining for processor, support logic, and memory device components was less than half of the total area.
For this application, each processor required 256 megabytes of DDR SDRAM. The designer initially considered using ten 512Mbit DDR SDRAMs in 60-FBGA packages to provide the necessary memory density, each of these FPGAs being 10 by 12.5 millimeters on a 1 millimeter pitch. These 10 devices would have 600 balls needing to be routed and would take up 1250 square-millimeters of PCB real estate. Given the system architecture requirements and limits, there simply was not enough space to fit this many components on the board.
To overcome this challenge, the designer selected two 256-megabyte, organized as 32M-by-72, 208-BGA DDR SDRAM memory devices. These two components are 13 by 22-millimeters each and require 572 square-millimeters of board space (over 50 percent savings over the chip-scale package solution) and 416 balls to be routed (30 percent reduction in I/O routing). These high-performance, high-reliability memory devices enabled the performance requirements to be realized in the limited area with the additional benefits of:
- 100 percent burned-in components for device reliability;
- standard Sn63/37Pb metallurgy ball arrays for the second-level reliability required in defense airborne applications;
- reduction of two layers in the PCB design which helps reduce the board cost; and
- upgradeability as the 256-megabyte DDR memory devices can be upgraded to 512-megabyte as 64M-by-72 in the same footprint as P3I or tech refresh is encountered.
Wherever high digital content and stringent space, weight, and height requirements exist, multichip semiconductor packages can offer a significant solution. At the component level, obsolescence can then be mitigated and significant value added by using upgrade paths in identical or compatible technologies. Most FPGAs support embedded soft microprocessors, such as Nios II that provide built-in obsolescence protection, especially compared to stand alone, discrete microprocessors. Engineers can take advantage of FPGA reconfigurability and soft processors to easily modify their design as needed.
Supplier selection in obsolescence management
While most suppliers of commercial off-the-shelf (COTS) components offer upgrades in memory products for commercial or military-grade components, few multichip manufacturers offer upgrades as standard products. Long-range roadmaps for future upgrades to higher densities are an important consideration in supplier selection. As military systems require tech refreshes or system upgrades, older ASICs and other components often go EOL. FPGAs can be used to provide similar functionality and enhanced performance on state-of-the-art technology nodes. This can extend the life of the overall equipment by 15 years or more. FPGAs also contain additional security and encryption features such as non-volatile key storage and 128-bit AES in Altera’s Stratix II, while Stratix III FPGAs have volatile and non-volatile key storage with 256-bit AES.
Another important aspect in reducing obsolescence is to ensure that the component supplier maintains a direct relationship with key silicon suppliers and closely monitors these suppliers for die-EOL or die-shrink situations to ensure source of supply and consistent performance. This allows advanced notification of die availability that can be managed by die storage or upgrades and action can be taken to address changes in electrical characteristics.
The military often buys through distributors, and as such may not receive notices of changes in components. MIL-PRF certified manufacturers have well-documented procedures that add the value of letting customers know when changes are being made. Risk mitigation is also enhanced if devices are manufactured in a DSCC-certified, Defense Department-cleared facility. This can provide for additional security and trusted supply.
Choosing the right component supplier can be as important as choosing the right component, especially when long-term planning and upgrades are considered, or when special features are required.
Jack Bogdanski is director of strategic development at White Electronic Designs in Phoenix. He has experience in multichip modules, memory and microprocessor devices, flip chip assembly, bump metallurgies, alternative alloys, and flexible circuits and laminates. Contact him by e-mail at firstname.lastname@example.org. Jeff Lamparter is senior business manager in the military and aerospace business unit for Altera Corp. in San Jose, Calif., a provider of programmable logic solutions.