Experimental Study Of Adhesion Characteristics And Surface Feature Of Gold Plated Contact Materials

The too large cold adhesion force between the gold plated contacts will lead to the failure of the function of the micro-relay directly. In order to find the relationship between cold adhesion force vs. surface quality of the gold coating and determine the physical mechanism of the cold adhesion phenomenon on the gold plated surface, a detailed experimental study and analysis about the influence of gold plating process factors on surface quality and cold adhesion force of gold coating is done using cold adhesion test rig and gold test rig.Firstly, a cold adhesion test rig of electrical contacts and gold electroplating test rig are designed in detail. The cold adhesion test rig can be compatible with three kinds of experimental samples: rivet contacts, unassembled reed pair and reed pair of half-assembled micro-relay. 3-D position adjustment of samples, displacement acquisition/actuation in nano-scale and force signal acquisition on micro cow level is realized in this test rig. The experimental process can be observed through optical assistant rig. Tiny parts can be electroplated by the gold electroplating test rig and the current parameters, solution temperature and rolling speed is adjustable.Secondly, optimum plating conditions composed of average current density, pulse duty ratio, solution temperature and stirring speed is found as the index of hardness and surface roughness. The relationship between coating thickness and plating time and the effects of solution temperature, average current density, pulse duty ratio and pulse frequency on the deposition rate is studied and verified experimentally. The influence of four factors mentioned above on of the gold coating is determined by comparing surface morphology under different plating conditions.Thirdly, the influence of four experiment parameters(surface morphology of the gold plating layer, coating thickness,maximum contact force and holding time) on the cold adhesion force of the gold plated surface is studied experimentally. The root cause of the influence of four parameters on cold adhesion force is analyzed through the corresponding conclusions from the experimental results combined with the previous studies and theoretical analysis and the direct factor that affects the cold adhesion force is determined.Finally, the mechanical reaction force characteristic curve of the actual micro-relay product is obtained using the cold adhesion test rig with the reed pair of half-assembled micro-relay as the test sample and analyzed theoretically. The feature points characterizing cold adhesion force in actual products and their extraction method is obtained. The influence of making/breaking speed of the test rig on cold adhesion force in a number of operation is experimentally studied and the mechanism of the influence is assumed by analyzing the dynamic force signal.The research results of this paper have reference significance for solving the problem of cold adhesion failure of gold plated contacts in the relay, and also has practical significance for improving the reliability of MEMS and micro-relay.