Publications

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Why Perform a WCCA?

This short white paper explores the Who, What, Where, When and Why of WCCA.

Worst Case Circuit Analysis - A Key to Program Risk Reduction For Managers

As space systems grow more complex and demand higher reliability, many programs face increased risk due to over-reliance on test, constrained engineering resources, and the growing use of COTS parts. Worst Case Circuit Analysis (WCCA) is a time-tested methodology that helps close the gap between what testing can show and what can actually go wrong. This presentation explores why WCCA is more critical than ever to ensuring mission success, particularly in the face of rising Electrical Power Subsystem (EPS) failures—a leading cause of satellite anomalies.

Optimizing Electronics Test/Analysis Ratio

Aerospace MRQW Reliability Conference Feb. 2020 - Reliability is a function of the amount of test and analysis applied. But programs are often budget and time constrained. So, what is the right ratio? For many programs, no analysis is performed at all as stress & derating and/or worst case circuit analysis are deemed "too expensive or too challenging." The usage of COTS components in high reliability applications to save money requires more analysis, not less. And the less we know about the parts and "reference designs" we use the more analysis we need. This paper discusses how we can use analysis to better complement our testing, Beginning- vs. End-of-Life (BOL vs EOL) tolerance impacts, and what circuit characteristics often fail stress and WCCA.

How WCCA Saves Money: The Case for Worst Case

Learn about the different ways in which worst case analysis saves money, board spins, and schedule, and supports continuous process improvement.

Introduction to Worst Case Circuit Analysis

Learn about skills and resources you need in order to be able to perform a worst case circuit analysis (WCCA) with this introductory presentation including detailed notes. Taken from various lectures and AEi Systems' own WCCA Training Workshop this PowerPoint Notes presentation discusses What WCCA is, Why and When to perform this critical analysis, Who should perform it, and What aspects drive the cost and schedule. Common issues found in WCCA are summarized and recommendations are made on how to improve the efficiency of the analysis effort. Finally, the new Aerospace TOR on WCCA is discussed by one of its authors, Charles Hymowitz (SME), along with its ramifications and future challenges.

Introduction to Automotive WCCA

This brief presentation discusses various aspects of Worst Case Circuit Analysis ("WCCA") with an emphasis on the needs of the automotive industry. It mimics AEi Systems' WCCA Training Workshop (WCCA Training) and is a good introduction for managers that are interested in learning about the basic requirements of WCCA.

Automotive WCCA Example Report - Simulating Stability and EMC/ESD Transients for Automotive Power Supplies

Performing WCCA for Automotive applications is not a trivial undertaking. Most SEVERELY UNDERESTIMATE the number of hours and resulting cost it takes to perform a WCCA for the functional blocks connected to the battery. It’s easily in the hundreds of hours, even for simple circuitry. This example shows why.

Lessons Learned from WCCA

We know that "Worst Case Happens Everyday" and we review a lot of WCCA performed by other companies. The quality of that work, as well as a desire to see the level of analysis improved, motivated us to write this paper. This presentation looks at two aspects: Lessons Learned from HOW we do WCCA, and Lessons Learned from actually DOING WCCA.

Tailoring TOR for Class D, Commercial Space, and Cubesat Missions

Presentation given by Charles Hymowitz at the NASA NEPP Workshop on 9.11.14. Discusses the reasons for performing Worst Case Analysis, the issues with using Testing as a substitute for WCCA, and the application of TOR-2012(8960)-4, REV. A Electrical Design Worst Case Circuit Analysis: Guidelines and Draft Standard principles to lower class and tech demo/cubesat missions.

Webinar: The Challenges of Automotive Worst Case Circuit Analysis

Want your module to be designed into tomorrow's automobiles? Worst case circuit analysis (WCCA) is no longer optional. It's now mandatory for compliance with automotive vendor requirements and various ISO standards. And for good reason. WCCA is a proven gateway to reliability. But undertaking WCCA is no joke. Product managers greatly underestimate the effort and the cost. WCCA is NOTHING like MTBF or FMEA. It is FAR more complex. The scope of the work – what analyses to perform – is almost never defined. And once they are defined what does it take to complete them within a tight schedule and with the resources/budget you have?

The Worst Case Blog

The Worst Case looks at the challenges associated with performing worst case circuit analysis (WCCA). This analysis is critical to many high reliability applications including those in the automotive, space, and medical fields. While its usage has been growing, the quality is often suspect. This blog focuses on a discussion of the skills, resources, and techniques required to properly perform a WCCA, as well as some of the reasons why WCCA is challenging to get right.

Post 1 - "Why WCCA is Challenging to Perform"

Looks at the challenges associated with performing Worst Case Circuit Analysis. The blog focuses on a discussion of the skills, resources, and techniques required to properly perform a WCCA, as well as, some of the reasons why WCCA is challenging to get right.

Post 2 - "Lack of Rigor will cost you"

The failure to do a rigorous job is the biggest problem with WCCA. There are many aspects to think about: Limited documentation, insufficient model correlation, tolerances that are not WC EOL, and the biggest, analyses completely left out. The impact of these deficiencies and the loss to ROI is discussed.

Post 3 - "Circuit and component models, getting them right"

Circuit models are the heart of WCCA. So why don't most WCCAs bother to correlate vendors' models? As with reference designs there is way too much trust. Vendor provided data and models are suspect until proven otherwise. The post discusses all the pitfalls.

Post 4 - "Monte Carlo Gone Wrong"

Why you are likely not performing this critical analysis correctly. The fourth post in the series talks about the pitfalls associated with performing Monte Carlo analysis and assessing its results. The two proper methods for electronics studies are covered including Tolerance Intervals for Normal Distributions and Distribution-Free Tolerance Intervals (nonparametric statistics) along with the correct number of trials you should be using for your analysis.

Post 5 - "Too Many Escapes and Biases"

"Escapes" is a euphemism for all the excuses programs, program managers, engineers, and reviewers use to curtail or eliminate WCCA associated activities. It is essential that all the elements noted in the (first) Going It Alone blog section, necessary to perform the WCCA, be brought together along with the right software, people, test data, and experience. With each hurdle, the analysis will stall, impacting the level of rigorousness, and the veracity of the conclusions. This article discusses the many excuses we use not to perform WCCA.

Post 6 - "The Fantasyland that is Resistor Aging"

Using 0.5%, or even 1%, for MIL-PRF-55342 resistor end-of-life effects? You might reconsider. It is probably not supportable. This article discusses resistor tolerances including the end-of-life tolerances for aging/combined environments in detail. Aging test data from SOTA is reviewed and assessed and calculations using Arrhenius equations are shown. Source control documents, mil-spec tolerances, stress, and accounting for temperature, time, and manufacturing effects are all discussed.