The Perception of Connector Testing
By Tom Peel, Contech Research

I’ve been asked many times during my tenure in the world of testing how to develop a proper test program and why it is of value to do so. In this next series of articles, I’ll present “myths, fantasies, and realities” that one might encounter during this process, in addition to the rationale, design, and layout of a meaningful test program.

Traditional testing represents the idea of “success testing,” where the requirements and severity levels are set to what a connector can do, as opposed to what it should do. Test durations are short, severity levels are weak, and requirements are broad. Testing should determine the functional capability of a design for the application in which it is to be used.

The basic prime tests to be included in any meaningful program fall into four categories: Electrical, mechanical, environmental, and application-specific. The following identify those tests, in addition to the rationale behind them.

A. Electrical
1. Low Level Circuit Resistance: The purpose is to evaluate the resistance characteristics of the contact systems under conditions where applied voltages and currents do not alter the physical contact interface, and will detect oxides and films that degrade electrical stability. This attribute is monitored throughout the test exposures. Electrical stability of the contact system is determined by analysis of the change in resistance that occurs following exposure to a particular test environment.

2. Contact Resistance at Rated Current: To determine the electrical resistance of the contact system under conditions where the applied current levels are at the rated current of the contact.

3. Current Carrying Capacity: To establish the current-carrying capacity of the connector system under evaluation. This is achieved by determining the temperature rise at the contact interface by at least three different current levels. The temperature rise at a given current level, plus the ambient operating temperature, should not exceed the temperature rating of the connector. Thus, the current rating of the system decreases as the operating ambient increases. This data may also be used to determine potential local “hot spots” internal to the connector, possible degradation factors, thermal effects on the adjacent positions, and the acceptability for the use of pulsing techniques.

B. Mechanical
1. Mating/Unmating Forces: To determine the amount of force required to engage and separate a connector pair.

2. Vibration (Random): To evaluate the effects of vibration within the predominant vibration frequency range and magnitudes that may be encountered during the life of the connector. The connector is monitored during the test to evaluate its susceptibility to contact interruptions or low nanosecond events. Vibration is also used to evaluate the impact on electrical stability of the contact systems when micromotion between contacting surfaces may be induced by mechanical means (eg. fretting corrosion).

3. Mechanical Shock: To determine the mechanical and electrical integrity of connectors for use with electronic equipment when subjected to shocks such as those expected from handling, transportation, etc. As with vibration testing, the connector is monitored during the test to evaluate its susceptibility to contact interruptions (nanosecond events).

4. Normal Force: To establish the magnitude of normal force (perpendicular contact force) generated at any given deflection level within the normal operating levels of the contact system. In addition, the magnitude of permanent set and its impact on loss of normal force due to stress relaxation is examined. This data and its relationship to contact force allow the electrical integrity and stability of the contact interface to be evaluated in proper perspective. Contact normal force is one of the most significant design parameters of a contact system.

C. Environmental
1. Temperature Life or Thermal Aging: To evaluate the impact on electrical stability of the contact system when exposed to a thermal environment that may generate temperature-dependent failure mechanisms such as:

• Dry oxidation of base metals and/or underplates that have reached the contacting surfaces due to impurities or by diffusion, pore corrosion, or intermetallic formation.

• Dry oxidation and/or film formation of particulates that may have been deposited on the contacting surfaces from the surrounding atmosphere.

• Dry oxidation due to smearing of base metal and/or underplates on the contacting surfaces or exposure of same due to wear.

• Reduced normal force due to thermal relaxation.

• Dry oxidation of the contacting surface when non-noble finish systems are utilized.

2. Temperature Cycling With or Without Humidity: To evaluate the impact on electrical stability of the contact system when exposed to any environment that may generate thermal/moisture-type failure mechanisms, such as:

• Fretting corrosion due to wear resulting from micromotion. Thermal cycling induces micromotion between contacting surfaces and humidity accelerates the oxidation process.

• Oxidation of wear debris that may have become entrapped between the contacting surfaces due to induced micromotion.

• Oxidation of particulates that may have been deposited on or entrapped between the contacting surfaces from the surrounding atmosphere.

• Via the wet oxidation process, detect loss of electrical stability due to particulates that may be deposited on contacting surfaces, wear which may expose base metal or underplates of contacting surfaces, and oxidation on non-noble finish systems.

3. Mixed Flowing Gas: Mixed flowing gas tests (MFG) are environmental test procedures whose primary purpose is to evaluate product performance under simulated storage or operating (field) conditions. For parts involving plated contact surfaces, such tests are also used to measure the effect of plating degradation (due to the environment) on the electrical and durability properties of a contact or connector system. The specific test conditions are usually chosen to simulate in the test laboratory the effects of certain representative field environments or environmental severity levels on standard metallic surfaces.

D. Application Specific: The tests, as indicated below, do not represent a complete listing, but examples where unique data has to be accumulated include:

• Dust

• Signal integrity (impedance, crosstalk, VSWR, etc.)

• Crimp tensile (crimp terminations only)

• Fluid resistance (military, aircraft, automotive) industrial cleaners

The basic test plan will contain, as a minimum, the tests indicated in items A, B, and C, above. The A tests are variable elements that are used to establish the basic functional capabilities of the system under test. This data can and should be formatted to determine the change in resistance that is important to determine electrical stability of the contact system. In the March 15 issue of Connector Supplier,  I will discuss the basic guidelines to develop a test program, along with some do’s and don’ts.

Thomas Peel is the president and director of test program development at Contech Research Inc. Contact tom at 508.226.4800 or tpeel@contechresearch.com.