Effect of Al-Trace Width on the Electromigration Failure Time of Flip-Chip Solder Joints

The effect of Al-trace width on electromigration (EM) in flip-chip solder joints was investigated experimentally. EM tests were performed on eutectic Sn-Ag solders with 40-mu m- and 100-mu m-wide Al traces. Under the same stressing conditions (0.5 A at 165 degrees C), the failure time was 44.1 h for solder joints with 40-mu m-wide traces and 250.1 h for solder joints with 100-mu m-wide traces. The Al-trace width influenced both the current crowding and the Joule heating effects. Thus, both effects are responsible for the significant difference in failure time. Finite-element analysis was used to examine the current crowding effect in solder bumps with Al traces of the two different widths. The results showed that the current crowding effect was slightly higher in joints with 40-mu m-wide traces. In addition, the temperature coefficient was used to measure the real temperatures in the solder bumps during EM. The results indicated that the width of the Al traces had a substantial influence on the Joule heating effect. The measured temperature in the solder bump was 218.2 degrees C and 172.2 degrees C for the bump with 40-mu m- and 100-mu m-wide Al traces, respectively. This difference in the Joule heating effect plays a crucial role in causing the difference in the failure time of solder joints with the two different widths.