Consideration of Voltage Drop in Power Contacts

The performance of power contacts was analyzed with respect to voltage drop change. This was done by simulating two known failure mechanisms, electromigration and fretting corrosion. A formulation was developed to simulate degradation of individual contact spots in each case. The analysis was conducted using Greenwood methods to calculate the resistance of multi-spot contact interfaces. In these cases, the position and size of each contact spot was varied randomly to provide multi-spot variations that occur in real contacts. As Greenwood utilizes the interaction of microcurrents, the method allows the calculation of currents in each of the multi spot contacts. Consequently, the current densities and contact resistance were calculated for the various cases considered. Moreover, the variation of current density due to spot size and position and also super temperature are included in the analysis. The effects from these variables were seen to degrade the conductivity of each randomly chosen contact spot. As expected, a reduction of contact spots and the associated contact area were shown to occur. Consequently, as the remaining contact spots carry greater micro-currents, they are seen to fail at accelerated rates producing a cascading effect leading to contact failure. The results of these analyses show aging produces instability due to contact loss, increased current density and super temperature. Also, an increase in voltage-drop by a factor of about 3 was shown to lead to a significant increase in probability of failure.