CALCE Research: Making Electronics Reliable and Cost-Effective
written by Thomas Ventsias
In 1985, when the U.S. Army asked the University of Maryland to update a handbook for predicting the failure rate of electronic components, it seemed at the time a fairly straightforward request.
The Military Handbook for Reliability Prediction of Electronic Equipment (known as MIL-Hdbk-217) and its commercial equivalents were widely viewed at the time as the industry standard all over the world. The goal behind MIL-Hdbk-217 was to ensure that the electronic components, such as transistors, diodes, resistors, capacitors, and switches, used in electronic systems could operate for long periods of time under demanding conditions.
After reviewing the document, however, Maryland researchers concluded that MIL-Hdbk-217 and the testing procedures behind it were basically flawed. "The methods in place [in 1985] were statistically oriented" says Peter Sandborn, associate professor of mechanical engineering in the A. James Clark School of Engineering. "[The Army] would ship 100,000 circuit boards, and after a period of time, would see how many came back with problems." From that information, he says, the U.S. Military built a model to determine how many circuit boards would fail. The major shortcoming of MIL-Hdbk-217 was its inability to address the fundamental cause of why and how electronic components and assemblies would fail over time. Consequently, these models were inaccurate, inapplicable as a predictive tool for new technologies, and could not be used to improve product design.
Researchers at Maryland offered an alternative. With research and input from across the academic disciplines, faculty in the Clark School started to push for a new process called "physics of failure (PoF) analysis". Based on the fundamental "physics" of each failure mechanism in each component (how it is built, how it operates, and under what conditions it fails) new models could be generated to predict aging, degradation, and failure over time. Using this same PoF knowledge, Maryland researchers soon developed new software that could "virtually" qualify electronic components via computer simulation.
These new ideas would form the basis for one of the largest research centers within the Clark School of Engineering.
The Center for Advanced Life Cycle Engineering (CALCE) Electronics Products and Systems Center (EPSC), established in 1986, is now an internationally recognized leader in reliability assessment of electronics based on PoF analysis. CALCE has grown into a consortium that has received almost $45 million in combined research support in the past 15 years. The center employs more than 100 faculty, research staff, and graduate students from almost every engineering discipline.
Much of CALCE's research is driven by the 50 - plus industrial partners who make up the CALCE consortium. A virtual who's who of leading electronics, aviation, automotive, semiconductor, computer and telecommunication companies like Lucent, Microsoft, and DaimlerChrysler, the consortium promotes research in areas that have an across-the-board impact on industry.
Current research at CALCE focuses on applying PoF knowledge for complex tasks such as designing electronics for reliability; accelerated testing; life consumption monitoring; supply chain management and parts obsolescence modeling; reliability of microelectromechanical systems (MEMS) technology; the role of electromagnetic interference in the design of electronics; and developing new environmentally friendly materials such as lead-free solders for "green" electronics.
An example of CALCE research is its fundamental work on computational failure models such as micromechanical simulations of cyclic loading in viscoplastic polycrystalline alloys like solders. These models capture complex creep fatigue damage processes under vibration and thermal cycling of electronic interconnects. Motivated by the understanding obtained from such detailed models, simpler models have been developed to facilitate design. These simulation approaches have been implemented into virtual qualification software for timely reliability assessment.
Getting It Right the First Time
In today’s fast- paced electronics industry, where time-to-market means everything, the use of physics of failure reliability modeling and virtual qualification can significantly shorten the time interval between design iterations.
"A month late to market on a mobile phone can be a financial disaster," says Peter Sandborn. But that's exactly what can happen if a manufacturer builds a phone and things start to fail in the initial production phase. Or worse yet, Sandborn says, if a company ships "bad" phones with inherent design flaws, not only do expenses increase dramatically by having to cover warranty costs, but the potential loss of customers can be extremely damaging. "There are big ramifications if these things go wrong," he says, "and a big upside if they can get it right the first time."
Helping design engineers "get it right" in the early stages of product development is a large part of CALCE's mission. This is accomplished by providing designers with the know-how to design in reliability rather than using a trial-and-error iteration to achieve reliability after the product is designed. When the CALCE approach was used on a particular General Motors product, they reduced development time by over 10% and increased first pass success by over 60%. PoF software tools developed at CALCE for analyzing circuit cards (calcePWA) and components (CADMP II) greatly facilitated that effort. CALCE's Physics-of-Failure software and methods have saved over $80 million in U.S. military programs, several million dollars on Westinghouse radar systems, over a million dollars on an AlliedSignal engine control module, and similar amounts on other military and commercial programs. Numerous commercial suppliers are now working with the CALCE to qualify new technologies, demonstrate reliability of new hardware, and trouble shoot existing warranty returns and field failures.
"With the scope, volume and time to market factor in the electronics industry today, there are a lot of people who are very interested in the types of problems that we are working on here at CALCE," says Sandborn.
A Smart Approach to Testing
CALCE has earned much of its international recognition for its breadth of expertise in developing accelerated life cycle testing methodologies for electronic parts and assemblies. Most integrated circuit boards or electronic assemblies are tested in the prototype stage to see if they will meet their expected life cycle. For electronic components used by the military or the aerospace industry, almost all need strict certification by agencies such as the Federal Aviation Administration.
Using state-of-the-art laboratories, researchers at CALCE have developed accelerated test methods that can effectively put many year's worth of wear and damage on an electronic component controllably in a few days or weeks. "It is a deceptively complex thing to do," says Abhijit Dasgupta, professor of mechanical engineering. "First, you need to understand what are the 'relevant' aging mechanisms, he says. "There's no point in designing an accelerated test that will stimulate failures that the product won't ever experience in the field but it's still done [in industry] all the time. Then you have to quantify the extent to which the test environment has accelerated the relevant aging mechanism, so you can extrapolate the test results to the use environment."
After determining the relevant testing factors, researchers at CALCE can create conditions of high temperature, high humidity, vibration, shock and impact, electrical stresses, and even high pressure or radiation if the electronics will be used in avionics or spacecraft.
In CALCE's high- altitude chamber, for example, researchers have represented changes in air pressure from sea level to 60,000 feet in the same time frame that it takes for an F16 jet fighter to do the same. "Companies who install a lot of electronic equipment on an aircraft, British Aerospace, and Honeywell, for example, have come to us to understand the effects of this type of environmental change on electronic failures," says Chris Wilkinson, a researcher at CALCE.
Putting the Parts in Place
Supply-chain management is a hot topic nowadays, and CALCE is leading the way in research involving electronic parts selection and obsolescence. Parts obsolescence is a major concern for low-volume, long-life electronic systems like those used in modern aircraft. One of the largest cost factors in designing a new airplane is maintaining an uninterrupted supply of parts.
When Honeywell wanted to build a new engine controller for an aircraft with a 10 year production life, they came to CALCE to optimize their parts selection for reliability and cost. "Due to certification requirements you can't change microprocessors on an airplane every 12 months like the PC industry," says Sandborn. With modern computer-generated models to predict obsolescence of electronic parts, CALCE can tell design engineers which part to put into their system, and can also predict when that specific part is likely to need replacement due to failure or obsolescence.
"CALCE was established to meet the needs of a growing electronics design and manufacturing industry," says Michael Pecht, professor of mechanical engineering and the director of CALCE. "We have grown significantly in 16 years, and can readily offer the latest resources and tools to help engineers assess, mitigate, and manage risks in electronic products. Our goal is simple: to offer the highest quality research environment to our sponsors, and to provide the world's best knowledge base for building reliable, competitive electronic systems."