Electrochemical Reliability as a Function of Component Standoff

A significant contributor to electrochemical related “no-fault found” customer returns are leakage current failures. Leakage current failures depend on the humidity levels, presence of ionic contaminants, and potential bias between metal interconnects on an electronic circuit. This type of failure is difficult to isolate as the fault may occur due to an initial interruption to functionality without further recurrence. Isolating the root cause of leakage current failures is gained by understanding proper design rules for low clearance components. One of the significant factors for controlling the water film formation and subsequent corrosion failure is the process-related contamination resulting from the reflow soldering process. The effect of flux residue on humidity related failures depends on the amount and chemistry of the residue, especially the ionic activator component in the flux component. The standoff height, from the assembly surface to the bottom of the component, factors into the level and activity of the flux trapped under the components termination. The purpose of this paper is to research the activity of flux residues as a function of the standoff height using insulation resistance. A second factor that will be part of this research is design options for outgassing flux residues.