Electrochemical migration (ECM) pose a high reliability risk to semiconductor devices. In this study, an ECM caused electrical failure case detail was shared, relevant electrical failure & ECM mechanism was also analyzed. To verify the failure mechanism discussed in this paper, ECM process was simulated on the same chip substrate. Besides, for the first time, the effect of chloride ion concentration with ECM was investigated on ball grid array (BGA) substrate by situ electrochemical, optical, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) method. Our simulation experiment results showed that on chip substrate level ECM process would hindered at relatively high chloride iron concentration, whereas it would occur quite fast at very low concentration. What's interesting is that even at 0ppm as long as the copper trace exposed into moisture environment, ECM process would also occur under bias condition.