粗糙表面微纳尺度接触电阻奇异性模型与原位分析方法的研究

The scale effect between two coarse mated metal surfaces becomes significant when the contact force and electrical current is decreasing to micro units. One of the critical reasons for electrical contact failure of micro electromechanical devices is the singular characteristics between contact resistance and contact load or the adhesion. Firstly, the surface morphology feature and constitutive relation of silver-base alloy and wafer Au-plated materials are determined based on the fractal random function and nano-indentation technique. Following the micro and nano scale contact resistance model of the rigid smooth sphere (and elasto-plastic coarse sphere) and elasto-plastic coarse plane are established individually by considering the surface force, material stress relaxation effect and conductive a-spot thermal stress effect simultaneously. In addition, the simulation method of mechanical-electrical-thermal coupled field by using Comsol multiphysics FEM commercial software is presented, and relative contact resistance singular characteristics and influencing factors are investigated explicitly during loading and unloading process. Furthermore, the multi-scale contact resistance in-situ measurement probe is designed for characterizing the electrical contact performance of contact material and micro structure evolution law of the materials' electrical contact performance. This project belongs to an applied fundamental research of inter-discipline involving electrical engineering and material science, whose research findings will be useful to evaluate the electrical contact performance of electric alloy and significant for reliability design of micro electrical apparatus.

微接触压力、弱接触电流条件将引起粗糙金属表面间尺度效应明显，出现的接触电阻突变或粘着故障是导致微小型电器元件电接触失效的根本原因。本项目首先基于分形随机函数和纳米压痕技术确定银基合金(和硅基)镀金材料的微观表面特征与微观本构关系，进而建立同时考虑表面力效应、材料应力松弛效应和导电斑点电流超温热应力效应的刚性光滑球面(和弹塑性粗糙球面)-弹塑性粗糙平面构成的微纳尺度接触电阻数学模型，通过Comsol Multiphysics有限元软件自编程机-电-热多场耦合数值技术，重点研究微纳尺度接触压力法向(和切向)加载、卸载过程中接触电阻奇异变化规律与主要影响因素。开发多尺度触点材料接触电阻原位分析实验系统，最终确定触点材料电接触性能的表征与微观组织结构演化规律。本项目属电气工程与材料学相交叉的应用基础研究。研究成果对电工合金材料电接触性能的评价具有实用价值，对电器元件可靠性设计具有参考意义。

本项目旨在确定微型继电器触点在弱压力、弱电流条件下的电接触失效机理和相关影响因素，因此分别开展了电接触特性原位测试分析系统平台的设计、具有镀层的测量压头与触点间的接触电阻解析建模与仿真分析、电接触建立过程与分离过程中出现的相关物理现象和机理的研究。研究成果如下：（1）自主开发设计了电接触特性原位测试分析系统平台，实现了测试系统五维位置可调、一维精密致动、致动位移—接触力—接触电压同步测量的功能，系统致动位置控制精度±10nm，接触力测量精度10μN，接触电压测量精度10nV。（2）建立了镀层结构的接触电阻模型，确认了电导率的差异导致接触对间存在电流收缩区、过渡区和基体区三个部分。（3）确定了触点电粘接现象主要由闭合过程材料熔融相变所导致，闭合过程中接触力与时间关系曲线呈负指数规律，衰减常数与粘接力直接相关；确定了粘接力断裂时的接触电阻与粘接力大小存在负一次幂的关系，由此说明粘接电阻的主要成分为金属体电阻而非膜电阻。（4）建立了粗糙球—平面弹性接触的物理模型，发现粗糙峰表面具有纳米量级的拉伸形变，且触点在压入纳米量级距离时冷粘力达到最大。实验验证了镀层材料、粗糙度和球面曲率半径对冷粘力的影响，接触压力的减小有助于降低黏着力。（5）发现了簧片触点对间微动摩擦将产生黏着力的现象，构建了有接触区域由多个接触斑点构成的模型，微动摩擦导致接触斑点内粗糙峰相互倾斜，并发生咬合造成微动摩擦黏着模型。（6）发现了镀金触点间的黏着力随微动幅值增大而增大，降低表面粗糙度可抑制触点黏着。