Say we have an engineer, Charlie, who is working on verification and reliability testing. Charlie’s company pushed to produce microelectronic circuits that could support robotic systems. To engage buyers at the Department, Charlie’s company had to show how his company would align with the “zero trust” approach for purchasing microelectronics. “Zero trust” assumes that nothing that the DoD purchases is safe and that everything must receive validation.
Unfortunately, Charlie’s company didn’t make the first cut or even receive a response. The issue wasn’t the product. Instead, the issue was reliability.
What is Reliability Engineering? Pursuant Perils
None of this made sense to Charlie. His designs had passed rigorous validation and verification tests. As he absently gazed at the company stationary, he thought he’d ought to rename it to Charlatan Microelectronics. When we speak about reliability assurance in electronic systems, though, we can’t spend time with charlatans, cons, imposters, or quacks.
Instead, the best practices found within Design for Reliability (DfR) provide assurance that a product will function as designed within a particular environment over a desired lifetime. DfR begins during the design analysis stage for electronic circuits and products and depends on the ability of a design team to determine the requirements for a PCB, system, or product.
Design for Reliability Processes in Electronic Design
The structured process used within DfR accounts for all types of changes that can occur from one end of the design process to the other. Specific data governs each aspect of the process. Structure also includes a sequence for using tools and methods within the design to ensure reliability. Depending on the scope and the requirements for the project, the sequence may occur linearly or may have some activities that occur in parallel with one another. The sequence may also vary from the design of one circuit or system to another.
The sequence for DfR wraps around six basic steps that help design teams develop a reliable product development roadmap. While DfR affects all aspects of the design and development processes, the key impact occurs during the concept and design stages. Design teams focused on DfR begin thinking about the possibility of failure early in the concept stage and maintain that focus while seeking methods to analyze and improve reliability.
An amalgamation of what goes into the DfR process.
Every project should begin with all stakeholders in mind. Whether working on circuit design for an aerospace application or on an industrial system that connects equipment to the Internet of Things (IoT), design teams must know about the operating environment and remain aware of expectations that may vary from vendor to end-user. A sharp focus on requirements often builds from those expectations while also remaining fixated on benchmarks, best practices, and an analysis of any competing products or systems.
Requirements Lead to Reliability Assurance in Electronic Systems
Design teams may define requirements by using a Critical to Reliability framework that discerns how electrical and mechanical designs respond to physical environments and applications. Depending on the application, those requirements may push circuits to consistently operate in conditions that have wide ranges of extreme temperatures and humidities, vibration, or shock. Other requirements may involve constraints such as physical size, flexibility, or dimensions.
Teams can develop risk models that include historical data for devices, an analysis of schematic design, the use of Worst Case Circuit Stress Analysis (WCCSA) and Failure Mode Effect and Criticality Analysis (FMECA), and estimates of failure rates. All this has the singular purpose of proving that circuits and components operate within or above design specifications for the life of the product.
Quantitative assessments drive Design for Reliability. The WCCSA factors in variances in component tolerances while depicting the functional performance of a circuit under extreme environmental or operating conditions. The analysis includes the manufacturer, the environment, component aging, fatigue, and tolerances while showing how a combination of factors can cause components to drift away from specifications.
Design engineers can use the FMECA to determine the impact of potential failure scenarios on circuits and systems. Failure Mode and Criticality Analysis occurs through fault tree analysis, modeling, and root cause analysis. In turn, design teams categorize the results of the FMECA according to the impact on success. With applications determining whether the definition of success covers only equipment, human safety, or a combination of equipment and safety, the use of the FMECA allows teams to:
Investigate design alternatives
Develop test methods
Establish benchmarks for reliability, maintainability, and safety
When a design team completes FMECA testing, the results provide information about single-point failures, critical failure estimates, system and sub-system failure modes, and the reliability of critical components. Individual parts of the information tree can indicate the possibility of a single-point or catastrophic failure. The entire set of information allows teams to identify reliability problem areas, devise a plan for eliminating or minimizing the problem areas, and potential design modifications that may include new technologies or components that have more precise tolerance and performance specifications.
The criticality analysis portion of the FMECA ranks the potential for failure by severity and probability. Each of the levels only provide a reference point for the analysis of the circuit for specific applications. Design engineers can use the criticality analysis to focus on significant components, circuits, sub-systems, or systems and to build an approximation of failure rates. The probability levels often change as circuit design becomes more mature.
Design for Reliability takes design teams on a different path. This path involves thinking in terms of tolerances not only terms of design but also in terms of factors that stress components and circuits. As a result, the idiom “the devil is in the details” comes to mind. Rather than accepting the results of a simulation, DfR involves a concentrated look at data while thinking of everything that may cause an unexpected problem.
This detailed analysis takes design teams away from assumptions that component X with Y percentage of tolerance will work in Z circuit regardless and points them to greater testing, analysis, and verification. Teams can extend the DfR process to continuously capture knowledge about component and circuit performance as a method for engaging improvement.
If you’re looking for design software that engages in both the collaborative nature of a reliable product design process and can provide the tools necessary to perform this testing, look no further than the suite of design and analysis tools from Cadence. Using OrCAD PCB Designer, you can start just about any design you might come across and move it through to production with ease.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.