Inside a connector an interface with low insertion force and contact resistance is required, utilizing low cost materials such as copper alloys surrounded by tin coating. Relating to the application, the operating parameters have a wide range of values of currents, forces and materials. In this paper, we present a new experimental method based on non-intrusive probing of the deflection of the spring terminal with a laser technique. The main feature is that the reflection of the Laser beam onto the spring allows the determination of the contact force of the lamella-spring inside the female part. The technique requires the following insertion parameters during the insertion stroke: contact deflection δ, which allows contact force Fc, insertion force Fi and contact resistance Rc. It was found that the insertion force has a maximum value which decreases to the stable value, and depends on the size and the material of the pin. However contact resistance decreases sharply when first inserting, and tends to stable values on completing the insertion process, which is less sensitive to the pin diameter. Furthermore the final value which is important for the connector characterization is related and discussed. Finally, discrepancies were observed between the experimental and calculated data with simple numerical models. More complex models are in progress, which should improve the convergence of the theoretical approach to experimental results and proceed to the optimization of the connector parameters.

In this paper, we try to establish a power law for contact resistance versus force Rc = KcFc-n , and we determine via experimental measurements and theoretical calculations, the constants n and Kc in the force range (1 mN-4 N) for bulk metal (Ag, Au, Pd, Ni) used in various applications (microswitches, connectors). The main experimental results of contact resistance are the occurrence of two decrease domains versus progressive load indentation. The first regime corresponds to the earlier touch of the coupon by the probe at force < 0.1 N. This elastic regime evolves to a plastic regime for medium force > 0.1 N. At the transition the exponent value n changes from 0.33 to 0.5 and induce Kc value increasing. Theoretical and computational approaches applied to the elasto-plastic model, confirm the occurrence of these two regimes. Although the calculated values of n are in good agreement with experimental values, some discrepancy between measured and calculated Kc values take place.