Dr. Bob on The How and Why of Connector Testing Programs
This article will provide an overview of connector testing programs in terms of procedures and purposes—the “how” and “why” of connector testing. Future articles will expand on this discussion to provide specifics and rationale for the test programs and individual test groups.
Beginning with the “how” of connector testing, consider the three basic components of a testing program: conditioning, exposure, and measurement. For example, a mechanical stability testing program may include some durability cycling as a conditioning step, followed by exposure to a mechanical shock environment, intended to simulate a particular field environment, such as automotive. The appropriate exposure for a given test is arguably the most important and difficult aspect in the development of a connector testing program. To define an appropriate exposure requires an understanding of the degradation mechanism and the driving forces for that mechanism. This requirement is the link between this testing series and the previous degradation mechanism series in ConnectorSupplier.com. This issue will be a recurring topic as this series on connector testing continues. For completeness, it must be noted that durability cycling can be either a conditioning procedure or an exposure, depending on the number of durability cycles specified. The difference between “conditioning” and “exposure” will be addressed in more detail during the discussion of individual test groups and procedures. Finally, a measurement must be taken at the beginning of the test sequence to establish a base line for the property of interest and also at the end of the test to assess the effect of the test exposures on connector performance. The most common connector measurement requirement is contact resistance, because an increase in contact resistance is a dominant cause of field failures of connectors.
Moving to “why” there are several reasons for testing connectors. They include:
- Design verification
- Performance verification
- Reliability assessment.
Each of these purposes uses the same basic test groups and procedures. Where they differ is in the details of any conditioning procedures and the selected exposures, both the severity and duration of the exposures. The key concern in exposure severity and duration is to define the relationship between the exposure and the intended application environment of the connector. In addition, the requirements for “passing” the test will be different for each purpose. This discussion will continue in detail after a complete review of a generic testing program has been completed in future articles in this series.
A generic test plan, following EIA 364 D, is shown. There are six groups in the test program. Five groups are “standard” and will be included in most test programs. The sixth group, supplemental tests, provides for flexibility in addressing special test procedures that may apply to a particular application or application environment; for example, an immersion test procedure that would be applicable to connectors intended for marine applications.
Note that each test group begins with at least one measurement, to provide a baseline value for the parameter being used as a requirement, followed by conditioning and/or exposure procedures, and concludes with a measurement to assess the performance of the parameter of interest in the test. A test group is usually identified in terms of the exposures included in the test. Note also, that only one test group includes an explicit preconditioning step, test group four. A generic test program of this type is generally conducted using separate samples for each group. The number and provenance of the samples depends on the purpose of the test program, as will be discussed in a later article. For now, some general comments on the test groups will suffice.
Test Group 1 is a mechanical test because the exposures are mechanical shock and vibration. This test group is intended to provide an assessment, or confirmation, of the mechanical stability of the connector under test.
Test Group 2 is a hybrid group because it includes mechanical, thermal, and corrosion exposures. It also specifies mechanical and electrical measurements. In addition, this test group includes characteristics of both specification/qualification and design verification tests. For example, a specification/qualification test is generally a “go, no-go” assessment, with measurements taken only at the beginning and end of the test. A design verification test, however, may incorporate multiple measurements to provide diagnostic capability. As mentioned, a detailed discussion of the purposes of testing, including qualification as opposed to diagnostic procedures, will be provided in a later article.
Test Group 3 is an environmental test group to assess the performance of the connector housing design/material, and includes thermal and humidity exposures and insulation resistance and dielectric withstanding voltage measurements.
Test Group 4 is a corrosion test group and includes an explicit preconditioning step. Preconditioning requirements, in this case, may include durability cycling and heat aging to condition the connector to some “life” state, e.g. half of the specified durability cycles and half of the temperature life of the connector, to assess the connector performance at that point in its intended application lifetime. Issues related to connector “life,” including an end-of-life (EOL) determination, will also be discussed in a following article.
Test Group 5 is a temperature life test group to assess the effects of stress relaxation on contact force. Two measurements are taken, mating/unmating force and electrical resistance, each of which is dependent on contact force, but for very different reasons.
Test Group 6, a supplemental group, is available to provide a capability to test for specific application-related conditions (e.g. automotive applications) with more demanding mechanical requirements or power applications that have additional qualification/performance requirements related to high current issues, such as temperature rise.
Each of the test groups and individual topics arising in the test groups, such as preconditioning, will be discussed in more detail in future articles. In the next article in this series, Max Peel, Senior Fellow of Contech Research, will provide his overview of this generic test plan from the perspective of a connector testing laboratory.
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