April 2018 - Interconnection Analysis

Developers and reliability professionals spend far more time with the intricacies and complexities of their design than with wiring and connectors. Yet, interconnection designs can cause unforeseen problems, some of which have been catastrophic. For example, the crash of Swissair Flight 111 was attributed to a fire caused by failures in power wiring associated with the entertainment system. This is not to imply that analyses alone would have prevented this tragedy, but to point out that low-tech designs like interconnection wiring should be given greater attention during the design process.

Connector failures are an ongoing risk for many systems. Short and open circuits in interconnection wiring can be caused by a connector’s bent pins, corroded pins, pushed pins (pins wiggled out of position due to improper installation), and pins with improperly crimped wire ends. Loss of redundant paths is another possible consequence of these failure modes. In each of these cases, a path is broken if the bent pin is part of an electrical path. Of course, a bent pin may also cause a short to a neighboring pin that is part of an unbroken path. In some connectors, a bent pin may short to two neighboring pins, a grounded shell, or a combination of these. If pin layout isn’t dense, a bent pin may also short to nothing.

Bent pin analysis determines every permutation of possible shorts due to bent pins, one pin at a time. However, it turns out that bent pin analysis is also directly applicable to analysis of short and open paths in interconnection wiring since a pin is part of a wiring path. What’s missing is that traditional bent pin analysis does not consider a short between two unbroken paths, or a short between an unbroken path and ground – like a grounded connector shell or a grounded cable clamp – often due to insulation failure.

However, bent pin analysis can be expanded to consider shorts between unbroken paths of adjacent conductors (called Cable Matrix Analysis, applicable to electrical cables where conductors are in fixed positions relative to each other), or between any two conductors in a bundle – including shorts between any conductor and ground. Based on each path’s signal type (power, ground, input, output, spare, etc.), Failure Modes and Effects Analysis (FMEA) produces a worksheet in which the analyst describes each failure mode’s effects at the low- and system-level, and sometimes at mid-level as well. The FMEA can identify potential single failures that can cause serious system-level effects, a need to add redundant paths, suggestions where paths should be further separated within a connector or bundle, and paths that should be routed via different connectors to improve reliability or safety.

To be sure, there are many other aspects of interconnection analysis that must be considered. These include effects from flexing, electrical and mechanical stress, electrical loading and heat generation, crosstalk and other electromagnetic phenomena, environmental deterioration, and aging. However, structured analysis of potential short and open paths remains a basic tool for minimizing potential failures of interconnection designs.

Through use of proprietary developed software, our solutions team can automate to automate traditional bent pin analysis, with the additional capability to perform cable matrix analysis between adjacent conductors and to analyze potential shorts between any two conductors, including ground. The software supplies many effect descriptions automatically (e.g., “No effect,” “No effect latent”) and automatically duplicates human-supplied descriptions for similar failure modes in different worksheet rows (for example, shorts between data bus paths in a bundle of wires will have the same failure effect descriptions at each level). If you think your interconnection wiring should be given greater attention, contact us today to see how we may assist you.

Blog post provided by Nat Ozarin, Senior Engineer, Omnicon
Tags: Bent pin, hardware, wiring path, bent pin analysis

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Omnicon provides custom engineering solutions for customers in aerospace, defense, transportation, medical and more.