The formation and growth of intermetallic compounds and shear strength at Sn–Zn solder/Au–Ni–Cu interfaces

Electromigration in the Ni/Sn-Zn/Cu solder interconnect was studied with an average current density of 3.51 9 10 4 A/cm 2 for 168.5 h at 150°C. When the electrons flowed from the Ni side to the Cu side, uniform layers of Ni 5 Zn 21 and Cu 5 Zn 8 were formed at the Ni/Sn-Zn and Cu/Sn-Zn interfaces. However, upon reversing the current direction, where electron flow was from the Cu side to the Ni side, a thicker Cu 6 Sn 5 phase replaced the Ni 5 Zn 21 phase at the Ni/SnZn interface, whereas at the Cu/Sn-Zn interface, a thicker b-CuZn phase replaced the Cu 5 Zn 8 phase.

Section: Introductionmentioning

confidence: 99%

Effects of Electromigration on Interfacial Reactions in the Ni/Sn-Zn/Cu Solder Interconnect

Zhang

Guo

Shang

2008

“…13 The development of these compounds has a major influence on the joint strength. 14,15 ) The fracture then propagated along the copper/intermetallic interface until it reached midway along the joint. At this point, it deviated at approximately 45°across the joint to the opposite side and then continued along that interface, as illustrated in Fig.…”

Section: Resultsmentioning

confidence: 99%

Strength of Soldered Joints Formed under Microgravity Conditions

Thomas

Atkinson

Dashwood

2007

Experiments have been carried out to compare the mechanical strength of joints soldered with Sn-Ag-Cu under different gravitational conditions. Joints soldered under microgravity (produced during a parabolic flight) have lower strength (by 32% in this case) than similar joints formed under normal gravity. Electron microscopy has shown that this is due to a larger volume of residual porosity (14%) in the joints formed in microgravity compared with <1% for joints formed in normal gravity. The residual porosity in joints formed in microgravity is mainly within the bulk of the solder, with some microporosity in the Cu 6 Sn 5 intermetallic layer near the copper interfaces. The porosity not only weakens the joint, but also biases the failure path away from the intermetallic layer and into the bulk of the solder. These observations show that gravitational buoyancy is important for the expulsion of flux and flux residues from soldered joints.

“…The reaction modes here are similar to those in the soldering of Sn-Zn on copper or ENIG, during which Zn-based IMCs are usually developed at the interface. 15,16 The reaction mechanism is believed to be that the dopant element (aluminum) acts as a dominant reactive species and restrains the diffusion force of tin atoms towards the interface. Therefore, Al-based IMCs are more thermodynamically preferred and stable than Sn-based IMCs.…”

Section: Discussionmentioning

confidence: 99%

Effect of Aluminum Concentration on the Interfacial Reactions of Sn-3.0Ag-xAl Solders with Copper and ENIG Metallizations

Xia

Jee

et al. 2008

Aluminum was added into Sn-3.0Ag (wt.%) solder to investigate the effect of aluminum concentration on the interfacial reaction of Sn-3.0Ag-xAl solders with copper or electroless nickel immersion gold (ENIG) metallizations. Four different Sn-3.0Ag-xAl solders (x = 0 wt.%, 0.1 wt.%, 0.5 wt.%, and 1.0 wt.%) were used for comparison. It was found that the composition, morphology, and thickness of interfacial reaction products were strongly dependent on aluminum concentration. At low aluminum concentration (0.1 wt.%), the typical Cu 6 Sn 5 layer was formed at the interface. When the aluminum concentration was 0.5 wt.%, a continuous CuAl 2 layer spalled off from the interfacial Cu-Sn intermetallic compound (IMC) layer. Only a planar CuAl 2 layer was observed at the interface when the aluminum concentration was increased to 1.0 wt.%. In Sn-Ag-Al/ENIG reactions, Ni 3 Sn 4 was formed and spallation occurred near the interface in the Sn-3.0Ag and Sn-3.0Ag-0.1Al solder joints. When the aluminum concentration was higher than 0.1 wt.%, a thin planar AuAl compound formed at the interface. There was no P-rich phase formation that retarded the spalling phenomenon. The aluminum additive in Sn-Ag solder inhibited the growth of IMCs in the reaction with copper or ENIG metallizations, which was favorable for the reliability of solder joints.