Reliability Evaluation of Underfill Encapsulated Pb-Free Flip Chip Package under Thermal Shock Test
Thermo-mechanical reliability of the solder bumped flip chip packages having underfill encapsulant was evaluated with thermal shock testing. In the initial reaction, the reaction product between the solder and Cu mini bump of chip side was Cu6Sn5 IMC layer, while the two phases which were (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 were formed between the solder and electroless Ni-P layer of the package side. A crack was formed at the upper edge region of solder bump, and propagated through the solder region. The primary failure mechanism of the solder joints in this type of package was confirmed to be thermally activated solder fatigue failure. After thermal shocks of 2000 cycles, one more crack which was not observed in the case of non-underfill encapsulated flip chip was observed at the left side of interface between solder bump and substrate. The addition of this crack formation should be due to the underfill encapsulation between the Si chip and substrate.
Hyungsun Kim, Junichi Hojo and Soo Wohn Lee
D. G. Kim et al., "Reliability Evaluation of Underfill Encapsulated Pb-Free Flip Chip Package under Thermal Shock Test", Materials Science Forum, Vols. 544-545, pp. 621-624, 2007