Shock, Rattle, and Vibrate with the EIA 364D – Group 1 Test per Dr. Bob
This article will begin the discussion of the generic test groups identified in EIA 364D: Electrical Connector/Socket Test Procedures Including Environmental Classifications. For reference, you can find the 364D generic test program in the first article in this series, “The How and Why of Connector Testing Programs.” The discussion begins with the first test group, which consists of the following phases:
Electrical Resistance – Shock – Vibration – Electrical Resistance.
This is the shortest test group in the generic program, but it provides a good springboard for preliminary discussion of an important aspect of connector testing philosophy.
The test group begins with an electrical resistance measurement to establish a base-line. which evaluates any contact resistance degradation that may occur due to the test exposures, shock, and vibration. The most commonly used electrical resistance measurement procedure is LLCR (Low Level Contact Resistance, Test Procedure 23, TP23), as discussed in a previous article in this series, “Measure Twice and Test Once,” although TP6, contact resistance at rated current (CRAC), is also allowed. The test group ends with an electrical resistance measurement to quantify any change in contact resistance as a result of the exposures of the test. If LLCR is used, DR, initial resistance minus end of test resistance, is the criterion. If CRAC is used, a MVD criterion will be applied, either a change in MVD or a maximum MVD criterion could be applied.
The electrical resistance aspects of test group 1 are straightforward, with the exception of relating DR or MVD to degradation levels that affect performance in the field. We will visit that issue in a later article.
Consider now the exposures, shock, and vibration that occur during a test, beginning with shock. This article will only comment generally on the exposures—details of the procedures will be discussed by Max Peel in the following article in this series. This first test group is essentially a screening test for the mechanical stability of the connector. It is well known, as discussed in the Connector Degradation series, that motion of the contact interface can be a driving force for several degradation mechanisms. These include fretting corrosion (primarily in tin-finished connectors), wear of the contact interface (all finish systems), and increased sensitivity to contamination (corrosion and particulates) around the contact interface. A connector system that has a high degree of mechanical stability will provide more stable performance in the field. Thus, the verification of mechanical stability is an important part of any connector assessment test program.
The generic test program in 364D does not specify a TP for shock, but the most commonly used is TP27, mechanical shock. The details of the exposure, in terms of excitation format, G level, duration, etc., are specified in TP27. For the purposes of this article, the main point is that the conditions specified in TP27 do not correlate to application conditions for connectors in the field. In fact, the TP27 conditions were selected to represent shipping conditions. It should be noted that there are other procedures for shock exposures. These include TP32, thermal shock (temperature cycling), and drop testing, which has no TP in 364D at this time.
The situation is similar with respect to vibration. No TP is specified in 364D, but TP28 is the most commonly used. TP28 contains a number of different exposure conditions with variations in excitation (sine or random), G levels, duration (time or cycles), and axis of vibration. Once again, these exposures do not correlate with application field conditions.
Both TP27 and TP28 were initially mil/spec exposures that have been carried over and applied to more generic application conditions of electrical connectors, as they are used today. The value of these exposures and TPs is primarily legacy and comparative. These exposures have revealed weaknesses in connectors, and connectors that have passed these exposures have had “acceptable” field histories. Thus, they have their uses in assessing connectors. In “The How and Why of Connector Testing Programs,” we discussed several reasons for testing connectors. They include:
- Design verification
- Performance verification
- Reliability assessment
The information derived from test group 1 is fully relevant to the first two purposes, though these exposures may be used in the latter two as well. The relevance of test group 1, to design verification and qualification/specification testing, is that these two are, loosely speaking, in the category of “go/no-go” test programs, and are in large measure comparative in nature and, therefore, the data can be leveraged against the known field performance history mentioned previously. The relevance of such qualitative field history to performance verification and reliability assessment is less significant. As mentioned in “How and Why,” performance verification and reliability assessment programs require knowledge of a more specific relationship between field degradation driving forces, the analog to exposures in a testing program, in order to enable some level of quantitative evaluation of connector degradation. The use of shock and vibration in such testing programs remains qualitative, and is primarily a legacy/comfort level validation because of the knowledge that mechanical stability is a significant factor in connector performance and reliability in the field.
In the next article in this series on connector testing programs, Max Peel will provide his insights into the implementation and selection of test procedures, and the relevance of the test results to connector evaluation.
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