The role of a nonconductive film (NCF) on Cu/Ni/Sn-Ag microbump interconnect reliability

Abstract

The use of a nonconductive film (NCF) to establish and enhance the stability of microbumps is crucial. Even though it is normal to apply NCF to microbump interconnection layers, understanding the behavior of microbump stability without the protection from a NCF is important. A free standing structure without a NCF can be used to determine the mechanical response of a single microbump. This information can be used to design robust interconnect structures. Electromigration (EM) tests were performed at 150 ℃ and 1.3 × 105 A/cm2 to investigate the effect of a NCF on the electrical reliability of Cu/Ni/Sn-Ag microbumps. The EM test results show different failure times and failure modes for Cu/Ni/Sn-Ag microbumps with the NCF and without the NCF. The microbump test samples with the NCF had a time to failure that was three times longer than that without the NCF. At a constant current density condition, the contribution of temperature-induced accelerated degradation and mechanical deformation factors were considered. A series of finite element and electron backscattered diffraction analyses revealed that the NCF restricted solder deformation and led to an increase in the back stress, which prolonged the EM lifetime.