Lifetime Prediction of Electrochemical Ion Migration with Various Surface Finishes of Printed Circuit Boards

Abstract

Electrochemical ion migration (ECM) can be generated by the electrochemical reaction between the anodic and cathodic electrodes of an electric circuit in the case of temperature, humidity and applied voltage. ECM can finally induce a malfunction of electronics due to precipitation of metallic ions in the cathode. In this work, we study the failure mechanism based on the identifying stress factor of ECM to occur and the accelerated life prediction of ECM occurrence. The modified Eyring model, which includes a stress model (temperature, humidity and voltage), is utilized to accelerate the life prediction of ECM. To obtain the temperature and humidity coefficient factors of ECM failure, an accelerated life test is conducted with a more than 50% failure of five types of test conditions, namely, 85°C/75% RH, 65°C/85% RH, 85°C/85% RH, 75°C/85% RH and 85°C/95% RH. The failure criterion of insulation resistance between the conductors is less than or equal to 10⁷ Ω. In situ monitoring of surface insulation resistance is performed throughout the temperature-humidity-bias tests for over 2600 h. From these results, we deduce the temperature and humidity coefficients of the acceleration model for predicting ECM time-to-failure in electroless nickel-immersion gold (ENIG) surface finish conductors covered with a solder mask. In addition, the electrochemical oxidation and reduction mechanisms of ECM are examined by physics-of-failure. Finally, we predict the B₁₀ life for ECM to occur on a FR-4 printed circuit board with an ENIG surface finish in use environment.