In Search of Standards: A Look at the iNEMI Connector Reliability Test Recommendations Project
A survey of industry experts underscores the need to develop standard reliability testing protocols for connectors.
Consistently testing the reliability of electrical connectors across types and use cases is a major challenge in the connector industry. Electrical connectors come in many shapes and sizes, and differ in use. In general, the purpose of an electrical connector is to allow an undisturbed electrical signal to travel between two points in a circuit. These are electromechanical in nature and also enable the circuit or circuits to be separated and re-connected with no unacceptable change to the signal integrity. Several different standards exist within the connector industry to evaluate reliability.
The iNEMI Connector Reliability Test Recommendations Project conducted a 32-question industry survey to determine common metrics for connector reliability guidelines across the industry. A broad range of industry sectors was represented in this survey. The majority of the individuals who responded were in a product development or quality/reliability position within their companies, while the rest of the respondents ranged in roles from component engineering to failure analysis. Participants reviewed four existing connector reliability testing standards:
- EIA 364F: Electrical Connector/Socket Test Procedures Including Environmental Classifications (developed and maintained by EIA committee CE 2.0)
- EIA 364-1000: Environmental Test Methodology for Assessing the Performance of Electrical Connectors and Sockets Used in Controlled Environment Applications (developed and maintained by EIA committee CE 2.0)
- ISO/IEC TR 29106: Introduction to MICE Environmental Classification (developed and maintained by a joint ISO-IEC committee JTC1/SC25)
- IEC 61586-TS: Estimation of the Reliability of Electrical Connectors (developed and maintained by IEC subcommittee 48B)
The team conducted a review of these standards relative to their roles in assessing connector reliability, with contact resistance being the primary performance criterion. A stand-alone connector reliability standard would be expected to provide the following:
- Definition of application stresses, preferably in some type of categories
- A test protocol stressing the potential degradation mechanisms in a manner that replicates what will occur in the actual application
- Specific test conditions to use in the defined sequence
- An evaluation procedure defining how data should be interpreted to provide a reliability assessment, either qualitatively indicating the part is fit for service in a specific class of application, or quantitatively by providing a numerical statement of the probability of the part operating throughout some stated lifetime
The EIA 364F standard provides a set of application categories divided into two types. The first type defines application categories based on the types and levels of stress expected in the application. The second type defines application conditions based on a type of use (e.g., automotive, aircraft, etc.).
The EIA 364-1000 standard was developed for evaluating connectors used in one specific application — business office equipment. It provides several test sequence protocols that incorporate all the primary connector degradation stresses.
ISO/IEC TR 29106
The ISO/IEC TR 29106 standard does not provide guidance on connector reliability testing. However, it does provide a system to define applications based on four categories of stress: mechanical, ingress, climatic/chemical, and electromagnetic.
IEC 61586 TS
IEC 61586 TS provides a high-level overview of the issues that make it difficult to provide estimates of connector reliability. The standard describes the different degradation mechanisms that may occur for the various contact alloys and plating systems used by the connector industry. It also defines standard reliability test sequences for connectors using noble and non-noble plated contacts.
The survey questions included a focus on three types of failures: operational, mechanical, and application. Next, the survey looked at how connector designers consider the performance levels given in IEEE Std. 1156.1-1993 when designing their connectors. The majority of the designers said they design and expect their designs to perform to level 5: Environment primarily intended for sheltered applications subject to minimal vibration, shock, or temperature variations (controlled indoor). Almost all of the survey participants designed custom solutions (e.g. board-to-board connectors for PCB mounting and I/O connectors).
Having a defined set of interconnect levels is beneficial in guiding development of reliability testing protocols. The level of interconnect is often closely correlated with the level of reliability required and with the number and range of detrimental stresses to which interconnects will be subjected.
A Proposed Connector Reliability Test Strategy
The reliability of a connector is a function of the application in which it will be used. Considering the variety of applications in which connectors are used, ranging from small, embedded, and portable devices to massive multi-purpose systems, it is not possible to define a testing protocol specific to all possible applications. In fact, identical contact types within the same connector may have very different performance requirements and be subjected to very different levels of stress.
Thus, in addition to the use of customized testing for a specific application, it would be beneficial to have standard testing protocols to provide an indication of reliability of connectors in an application class. The fact that the industry reliability standards reviewed define application classes indicates an industry recognition of the utility of this approach. The typical conditions in these classes can serve as a guide for developing common connector reliability evaluation plans.
Development of application categories based on physics-of-failure to target an application’s landscape from usage to environmental condition should be considered to determine a connector’s overall expected performance level. A physics-of-failure view of the primary causes of connector electrical resistance failures finds two stress categories common to almost all applications, and these must typically interact to cause an electrical resistance failure at a contact interface. The first cause is environmental and the second is mechanical and these are, in fact, the primary stress types noted in the connector reliability standards reviewed. It should be noted that, in addition to stresses experienced while a connector is in service, use conditions are comprised of various elements, from the material to device fabrication to product level or system assembly and transportation (shipping/handling) until the end-user destination.. Therefore, appropriate stresses other than application class-defined levels of climatic and mechanical stresses would likely be included in any reliability testing protocol. Knowledge of the ultimate planned use of the connector would be needed to properly determine the inclusion of these additional stresses.
The project team concluded that there is agreement on the need for some common approach to assessing connector reliability. They also concluded that there is sufficient agreement on definition of levels of interconnect and on primary connector test methods to allow a structure of common application classes and related test conditions to support an effort to develop standard reliability testing protocols for connectors.
This paper was published in the Proceedings of SMTA International, Rosemont, IL, September 25-September 29, 2016. To read it in its entirety, visit iNEMI.org.
Contributors to this paper: Benson Chan, Integrated Electronics Engineering Center (IEEC), Binghamton University, US; Philip Conde, Dell, US; Christian Dandl, Rosenberger Hochfrequenztechnik GmbH & Co. KG, Germany; Ife Hsu, Shane Kirkbride (Phase 2 Project Chair), Keysight Technologies Inc. US; Bob Martinson, Lotes, US; Vince Pascucci (Phase 1 Project Chair), TE Connectivity, US; Anne Rayan, Alcatel-Lucent (Nokia), US
The International Electronics Manufacturing Initiative’s mission is to forecast and accelerate improvements in the electronics manufacturing industry for a sustainable future. This industry-led consortium is made up of approximately 90 manufacturers, suppliers, industry associations and consortia, government agencies and universities. iNEMI roadmaps the needs of the electronics industry, identifies gaps in the technology infrastructure, establishes implementation projects to eliminate these gaps (both business and technical), and stimulates standards activities to speed the introduction of new technologies. For additional information about iNEMI, go to https://www.inemi.org