Real-time Monitoring of Electrochemical Migration during Environmental Tests

More and more reliability and quality problems of electrical assemblies have to be solved due to the trend of miniaturization and the even higher level of integration. In some cases these failures can lead to catastrophic failure. The phenomenon of electrochemical migration is one of the most dangerous failure mechanism which usually results in short resistive circuits. In this paper electrochemical migration (ECM) failure phenomena is be investigated which was real-time monitored by the measurements of electrical parameters of conductor patterns with immersion Ag and immersion Ag finish coated with Sn60Pb on Printed Wiring Boards (PWB.) Highly Accelerated Stress Test (HAST) and Thermal Humidity Bias (THB) tests were carried out and Mean Time To Failure (MTTF) comparison was investigated between immersion Ag and immersion Ag coated with Sn60Pb. Only preliminary investigations were presented in order to determine the steps of the full ECM process on different substrates, surface finishes, solder alloys under various climatic conditions. The key findings were that the MTTFs during HAST tests were significantly shorter than in case of THB tests.