This induces a significant decrease of the contact pressure held between the wires and at the wire-barrel interface, which in turn increases the contact the resistance. Such phenomena, either creep flow or recrystallization processes, are not spontaneous and requires high temperatures. For instance, Cu recrystallization is induced at temperatures higher than 120 ºC whereas Cu creeping requires higher temperatures.
Improper crimping:
Care should be taken neither to damage the insulation of the wire strands nor to leave insulator residues over the stripped conductor. Crimping must be performed according to the manufacturer’s specification, and special attention must be paid to the barrel and wire compatibility, as well as the suitability and calibration of the crimping tool that determines the applied force and the reached insertion depth. Failure to follow the manufacturer specifications results in poor crimping with negative effects on both the mechanical strength and the contact conductivity, as illustrated in the figure.
Diagnosis tools:
In general, improper degree of compression and related issues can be detected either by mechanical tests such as tensile strength test or metallographic cross-section inspection of the crimped area. In the latter case, a comprehensive inspection must check several factors: the void percentage, the barrel and wire deformation, braids distribution and the barrel and wire integrity. The figure compares crimped connectors analyzed in our laboratory. One of the examples shows a large percentage of void area, which is an indication of a low degree of compression and poor electrical contact as well as a rejection cause according to the specification ECSS-Q-ST-70-26C, applied in European Space Agency (ESA) projects.
Examples of Connectors rejected and accepted iaw the specification ECSS-Q-ST-70-26C
Failures in crimped connectors can be related to different causes, some of which have been discussed elsewhere. The present post analyzes those related to improper degree of compression.
References
1. Electronics Engineer’s Reference Book, Butterworth International Edition, Ed. L. W. Turner
2. Electronic Failure Analysis Handbook, McGraw-Hill, Pierry L Martin.
3. RADC-TR-78-15 Air Force Systems Command.
4. Materials and Processes for Spacecraft and High-Reliability Applications, Springer, Barrie D. Dunn.
5. Identification of corrosion and damage mechanisms using scanning electron microscopy and energy-dispersive X-ray microanalysis: contribution to failure analysis case histories, IOP Conf. Ser.: Mater. Sci. Eng. 55 012015, G Pantazopoulos and A Vazdirvanidis
6. Use of Thermography and Ultrasonic Inspection for Evaluation of Crimped Wire Connection Quality, 18th World Conference on Nondestructive Testing; Matej FINC, Tomaž KEK, Janez GRUM.
*included all “Improper degree of compression in Crimped Connectors”, “Corrosion/Contamination in Crimped Connectors” and “ Electrothermal events Crimped Connectors