Reliability of automotive connectors coatings

Working in the transport field

Mélanie Bordignon is a doctor of MINES ParisTech since the first of December 2009



Pursuing a doctorate after obtaining her engineering degree in 2005 from ESIREM (Ecole Supérieure d'Ingénieur de Recherche en Matériaux), and a CIM master diploma (Chimie des Interfaces des Matériaux) was logical for Mélanie Bordignon and she wanted to work in the transport field.

She began to work in january 2006, for the Centre of materials of MINES ParisTech and Renault, and at the end of her thesis, she looked for a job that may call upon her skills not only concerning connectors but also materials in general, and was hired by Alstom Transport in June 2009.

Her role consists in deciding on conclusions to derive from environmental and mechanical testing of connectors and cabling, for train applications. She is also in charge of beginning eco design activities at the site, which is mainly a materials concern, dealing with environmental aspects of materials, from extraction, during processing and lifetime, all the way to end-of-life recycling.

CIFRE contract

Hired with a CIFRE contract (Industrial Convention for Formation by REsearch)  by Renault, to work on the reliability of tin coating for automotive connectors, she shared her time between the Centre of materials of MINES ParisTech and the Renault Technocenter, with the objective to determine if tin coating was the right solution for a utilization on connectors in an engine environment, i.e. with an elevated high temperature.

The first part of her thesis consisted in studying the interdiffusion kinetics between the base material used for connectors, a copper alloy, and the tin coating. Indeed, temperature is an accelerating factor for interdiffusion, and it leads to formation of intermetallic compounds, the properties of which, such as hardness and tribology behaviour are different from pure tin. It was shown that parameters such as the nature of tin (matte or bright), the presence of alloying elements in copper, or the utilization of a nickel underlayer were playing a major role on interdiffusion kinetics.

Secondly, aged and non-aged connectors were tested under a current load, and the sensitivity to Joule effect was measured. It was shown that coating hardness was decisive because it played a role in the establishment of a significative contact area. When area is restricted, the current lines are constricted, and ohmic loss cause an elevation of temperature at the contact point.

Eventually, the reliability of contacts was estimated under a vibration rate. Connectors in vehicles are submitted to vibrations that may come from the engine, the road and the suspensions. These vibrations provoque a relative displacement at the contact point of the connector. When using plating, corroded particles comes at the contact point, and this third body acts as an electrical insulator and causes an elevation in the contact resistance. This is one of the main failure mode of connectors. It was shown that a limit sliding amplitude exists, under which no degradation is observed on the contact. This limit is different according to the ageing state of the coating.
It was shown by lifetime tests that tin was underwert wear and corrosion, leading to insulation due to the presence of tin oxide, whereas intermetallics had a fragile behavior, with particles ejected out of the contact point, leading to an exposure of the substrate and insulation caused by the presence of copper oxide.


The impact of temperature on the lifetime of automotive connectors and the determination of possible mechanisms to explain differences observed between aged and non-aged samples gave to Renault precious information about the performance of tin plated contacts. Suggestions for material choice were made according to the location of the connector in the vehicle. Results also led to adding precisions in the Renault Specification For Connectors. Renault also made up its mind concerning suppliers’ proposals to provide connectors with 100% converted intermetallic coatings.