In situ optical inspection of electrochemical migration during THB tests

In order to get more information about the process of electrochemical migration (ECM), a novel in situ optical inspection system was developed and tested. The optical inspection system is applicable for real time in situ investigation to observe water condensation and dendrite growth during Thermal Humidity Bias (THB) tests. In this paper, a real time observation of water condensation and dendrite growth is studied on immersion silver (iAg), bare copper (Cu) and galvanic tin (gSn) interdigital (double comb) patterns prepared on FR4 substrate during Dew Point THB test. The real time in situ optical investigations were verified by real time voltage measurements, which are presented in the paper as well. The result shows that the water condensation mainly starts on the metal surface, which is an unexpected phenomenon since the preliminary condition of ECM is the presence of a continuous moisture film between the metallization stripes, e.g. on the surface of the insulation board material.