ANALYZING AND PREDICTING ELECTROCHEMICAL MIGRATION FAILURES ON FIELD FAILURE RETURNS

摘要

Electrochemical Migration has been discovered on your assembly after burn-in, or worse yet, on a product returned from the field. A leakage current developed between two isolated circuits and a short circuit occurred. You build IPC Class 2, Dedicated Service Electronic, and Class 3, High Performance Electronic, Products, so this type of failure is of great concern to your company. You want to know if this is an isolated incident or is your whole lot in danger of failing in the field? This article outlines options that are available to analyze this specific lot of assemblies and steps that can be taken to prevent ECM failures on future lots. IPC J-STD-001, Requirements for Soldered Electrical and Electronic Assemblies, is used as a guideline in preparing a customized test procedure. This article outlines exact procedures that may be used to assess non-failed assemblies for ECM potential. Case studies are included. The general procedure is as follows: Monitoring points connected to the area of concern are isolated, often by removing components or cutting other traces and wires are soldered. The assemblies are placed in a temperature/humidity chamber and a bias is applied across the suspect location. The resistance between these isolated points is monitored for sudden or slow drops that are indicative of leakage current development or dendritic growth. If ECM development is observed on these assemblies from the same lot, the entire lot should be considered at risk.