Connector Reliability Modeling

Project Number: C93-05
Point of Contact: pecht@calce.umd.edu

Objective

Develop a physics-of-failure based framework for reliability model of connectors that accounts for stress relaxation, durability cycles, and the environment. Evaluation of mission profile stresses will be accomplished with acceleration factors from Battelle.

Background

The reliability of electronic systems is largely dependent on and significantly impacted by the performance of various connectors in the system. Electrical connectors must to have low and stable contact resistances during service life. Connector service life is a function of various factors, including the thickness of plating, stress relaxation in the material of the spring, wear of the contact finishes, corrosion, ambient temperature, humidity, shock, and vibration. The useful life of a connector ceases when the contact resistance exceeds a certain limit value.

 As part of the 1992 research, CALCE performed data analysis on the MFG contact resistance versus normal force data, and used statistical tools to model the contact resistance as a function of the connector materials, the usage environment, the time in the usage environment, and stress relaxation in the contact springs. A contact-physics model based on the classical Holm's equation was used to develop and relate the experimental contact resistance data to normal force and aging.

Work Accomplished

• The modeling approach combines the use of classical contact physics laws with stochastic treatment of experimental data from the Mixed Flowing Gas (MFG) test performed by AMP Inc. in accelerated environments.
• Stress relaxation in the contact springs is modeled as a function of time and usage temperature using the Stennet, Ireland, and Campbell approach.
• Wear in the contact finishes is modeled as a function of normal force and plating thickness, using the results of wear tests conducted on metallic coupons and actual connector samples.
• Two sets of wear tests were conducted on gold-plated connector samples, using a wear-testing fixture to simulate actual field conditions of mating and unmating. These wear-tested pins and springs were cross-sectioned at the wear tracks and observed under the scanning electron microscope (SEM) to determine the reduction in gold-plating thickness with cycling.  
• A mechano-stochastic connector reliability model has been developed that accounts for durability or mating cycles, stress relaxation of the contact spring members, and exposure to mixed flowing gas (MFG).
• An alpha version of the connector reliability software model is available.