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Ask Dr.
Bob
The How and Why
of Connector Testing Programs
By Dr. Robert S. Mroczkowski, Bishop
& Associates Inc.
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:
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.
Send your connector testing questions to
AskDrBob@ConnectorSupplier.com.
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Dr. Robert S. Mroczkowski
Director Technology, Bishop and Associates Inc.
In 1998, Dr. Mroczkowski founded connNtext associates, a
firm providing consulting services in connector applications
to the electronics industry. Dr. Mroczkowski has over 30
years experience in various aspects of the electronics
industry. He joined AMP Inc. in 1971. While at AMP, his
responsibilities included consulting on connector design,
materials, and reliability concerns within AMP, and
providing an interface to AMP customers on the same issues.
In 1990 he joined the AMP Advanced Development Laboratories,
where he was responsible for the development of microstrip
cable connectors and a new microcoaxial connector for
medical ultrasound diagnostic equipment. Dr. Mroczkowski
retired in 1998 as an AMP principal. He is the author of the
McGraw Hill Electronics Connector Handbook, has
contributed chapters on connectors and interconnections to a
number of packaging handbooks, and written more than 20
technical papers. He holds seven patents. In 1997, Dr.
Mroczkowski received the Lifetime Achievement Award of the
International Institute of Connector and Interconnection
Technology.
He holds a bachelor’s, master’s, and doctorate of
science degrees in physical metallurgy from the
Massachusetts Institute of Technology..
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