Ruggedization & Reliability
Engineering and manufacturing advanced, embedded computing products for harsh military applications requires a breadth of expertize and hands-on experience that only an industry leader like Curtiss-Wright Controls Embedded Computing can command. At CWCEC we apply rigorous processes developed through many years of funded research, to build products that are designed from the ground up to give years of reliable operation in extremes of operating temperature, shock, vibration and corrosive atmospheres.
Curtiss-Wright’s products are available in 4 ruggedization levels covering requirements from Naval between-decks, through tracked land vehicles, helicopters and manned aircraft right through to the latest generations of unmanned air vehicles. Products may be air- or conduction-cooled depending upon their end-use application. Conduction-cooled construction is more rugged, incorporating additional stiffening at the top, bottom and center of the product. The use of wedgelocks at the board’s edges provides further mechanical integrity while providing a low impedance thermal path between the board and its chassis. Conduction-cooling is preferred for the most severe environments.
Designing For Deployment
Deployment demands reliability, maintainability and upgradeability as well as the more usual COTS product attributes of high performance, rich functionality and affordability. Curtiss-Wright invests heavily in research into advanced packaging techniques including materials technology and advanced cooling such as heat pipes, evaporative, immersion, liquid and air flow-through. Our advanced research has contributed to the development of 6U profile VMEbus boards able to dissipate an industry-beating in a conduction-cooled environment.
Curtiss-Wright is a leader in leading VITA working groups defining the next generations of technology such as VPX (VITA 46) which will greatly enhance VME’s connectivity and introduces backplane connectors suited to future generations of switched fabrics with bit rates of up to 6.25Gbps.
Curtiss-Wright’s design philosophy is to use the best commercial parts and design them into a rugged product to withstand extremes of temperature, high levels of shock, vibration and environmental hazards day-in, day-out without failure. Military qualified components are no longer available for many of the advanced, high performance functions demanded by modern military systems. Commercial components are generally only characterized by their manufacturers for their volume markets, however many of these components have inherent design margins well-suited for use in harsher environments and these are selected for preference. Curtiss-Wright has developed rigorous procedure including construction analysis, temperature cycling and die integrity to ensure that all parts meet our exacting needs.
Software Quality is a vital element of deployed reliability. Many hardware products are supplied with on-board firmware, libraries, drivers and board support packages (BSPs). These are developed internally and exhaustively tested with a wide range of Curtiss-Wright hardware and software products for compatibility and interoperability before being released as production-ready packages. With a long tradition of software development to DOD-STD-2167A and MIL-STD-489, Curtiss-Wright has evolved software development and configuration management standards in accordance with IEEE 12207 with additional audit and QA derived from our compliance to ISO 9001 and AS 9100.
Thermal design must be modeled accurately to ensure that maximum die temperatures are not exceeded. Curtiss-Wright models the effects of conduction and air cooling using FEA and CFD packages, having verified over many new product developments that modeled die temperatures are representative of actual production boards. Curtiss-Wright is renowned for developing innovative solutions to increase power dissipation while remaining within device limits. Some examples are:
TherMax thermal frame design to increase heat-flow from components to the external thermal interface.
Heatshunts from hot components to an unused chassis interface above the wedgelock.
Heatshunts from high power PMC modules directly to the thermal interfaces.
The first effective product development using heatpipes to cool a very high power processor device.
Mechanical Design is also modeled using FEA tools. Curtiss-Wright conducts regular tests on new components and, in particular, connectors to ensure their integrity on representative boards. As the functional density of new products increases, so does the complexity of its printed wiring board (PWB), causing feature geometries and fine lines to shrink even further. This reduction of size introduces increased mechanical stress during repeated thermal cycles causing buried vias, plated-through holes and micro-vias. Curtiss-Wright has adopted an enhanced FR4 material for all its rugged products and introduced Interconnect Stress Testing (IST) to weed out faulty PWBs prior to assembly.
Solder Joint Reliability is critical to the long term deployment of our products. Military applications experience thermal stress due to their extreme operating temperature range. This can cause failure of solder joints due to mismatch in rates of thermal expansion between components and the PWB. We conduct extensive research into the selection of component packaging to ensure compatibility with the PWB material. We also continuously evaluate new underfills, solder alloys and PWB materials to ensure the highest standards of reliability for every new product development.
In response to the RoHS and WEEE directives from the European community we recognize that continuing to ensure our products meet our customer’s stringent reliability standards is of paramount importance. As a result, our Ottawa manufacturing facility that supports our Virginia, San Diego and Ottawa product lines will continue to produce all existing products with a SnPb manufacturing process, to ensure we can guarantee the reliability of our products in the extreme application environments so commonly found in the Military and Aerospace markets.
We are working closely with our component suppliers to create a controlled environment that ensures the proper usage and identification of SnPb and PbFree components in our Engineering CAD and MRP parts databases. We also have an active Solder Joint Reliability (SJR) program that assesses different technologies including the reliability of SnPb re-balled parts. As we move into the future, Curtiss-Wright will be monitoring the several industry standards groups who are addressing the impact of PbFree. In addition, our Engineering Services Group will continue to be actively involved in the Lead-Free Electronics in Aerospace Project (LEAP). To verify design integrity all new products are subject to a strict qualification exercise. Environmental testing is performed to MIL-STD-810F guidelines and as a final check the product is subject to a Highly Accelerated Life Test (HALT) to stress the design margins at extremes of temperature to identify any potential weaknesses in long term reliability.
Deployment in military applications requires that equipment can be unambiguously diagnosable, repairable and upgradeable in very arduous conditions. Unlike many COTS items, Curtiss-Wright’s products have designed-in maintainability features in both hardware and software ideally matched to military service requirements.
Extensive Built-in Test (BIT) routines ensure a high degree of confidence in the health of the hardware. In addition to basic BIT functions, additional hardware such as watchdog timers and thermal sensors are provided for the user to incorporate at the application level. Curtiss-Wright supports diagnostic tests, each available with a detailed coverage analysis, at three levels:
PBIT – basic power-up BIT which runs at switch-on. It tests that the board’s functionality is ready to support an operating system and the next higher levels of testing.
IBIT – initiated BIT routines which are called to make extensive tests of individual functions.
CBIT – continuous BIT providing routines which can be called on a repetitive basis from the operating system during normal operation of the equipment.
I/O Connections are made through the backplane, even from PMC modules which pass through their host board to the backplane. This is the preferred method of board-level connectivity as it allows individual boards to be swapped easily and safely from a chassis. Curtiss-Wright embodies this total backplane connectivity into its conduction-cooled chassis and subsystems development activities, providing the most space-efficient and maintainable overall subsystems packaging.
The need to be regularly upgraded has become a key attribute of today’s embedded computing products using COTS components, some of which have a lifetime of 12 months or less. However, Curtiss-Wright’s component selection procedures during design ensure product lifetimes of at least five years. The rapid rate of technological change and the adoption of spiral development methodology often results in planned technology refreshes during all phases of development, production and deployment. Curtiss-Wright‘s products have been designed to support this regular refresh with continuing generational compatibility of like product lines an inherent feature of their design.
World Class Manufacturing
Rugged products are manufactured in our own world-class facility optimized for high-mix, high quality and small batch sizes typical of military requirements. Equipped with the latest SMT assembly, cleaning and X-ray inspection equipment, our operations are AS9100 and ISO-9001 certified and we comply to the highest standards of workmanship defined by IPC specifications. All materials and processes are controlled by our enterprise-wide SAP system which offers full component traceability to individual products by serial number.
Following full functional testing, newly manufactured products go through an Environmental Stress Screen (ESS) running functional test software. Hot and cold starts and variations of supply voltage are applied to weed out any early component failures or manufacturing defects.