Au-Sn Intermetallic Compounds Research Articles

Creep-fatigue life prediction of in situ composite solders : Kuo, C.G., Sastry, S.M.L. and Jerina, K.L. Metall. Mater. Trans. A (1995) 26A (12), 3265–3275

Initial success of new fluxless flip–chip interconnect technique is reported. Non-eutectic Sn-rich SnAu solder bumps are used to connect thin silicon chip to glass substrate and Cu laminated polyimide film, respectively. Fluxless process development on tin-rich alloys is challenging because tin atoms get oxidized easily. The solder bumps of SnAu multilayer composite with overall composition of 95 at.% Sn and 5 at.% Au are fabricated by vacuum deposition on thin silicon wafers to prevent solder oxidation. The bonding is performed at 250 °C in hydrogen environment without using any flux. The diameter of the bump is 200 μm and height is 20 μm. Nearly void-free solder joints with randomly distributed AuSn4 intermetallic compound (IMC) are produced using this fluxless bonding process. Continuous layers of Cu3Sn and Cu6Sn5 instead of commonly known scallop-type Cu6Sn5 are formed between laminated Cu layer and the Sn-rich non-eutectic AuSn solder. The re-melting temperature of solder joints is measured to be 220 °C. The bonding process is entirely flux-free and thus is particularly valuable for many devices that cannot take any flux, such as biomedical, photonic, MEMS, and sensor devices.

Reaction processes between silver or zinc doped Pb–Sn solder and gold

The microstructures of soldered joints made on gold using silver or zinc doped Pb–Sn solder have been studied in the scanning electron microscope before and after accelerated aging. Layers of Au–Sn intermetallic compounds form between the unreacted gold and the solder as a result of the diffusion of gold through the product layers. The reaction kinetics has been studied as a function of temperature for the silver doped system and, in the initial stages, was found to be parabolic with an activation energy of (0·86±0·03) eV. This is the same as for joints made using undoped Pb–Sn solder. As in the undoped system, the growth of the product layers subsequently fell below the t1/2 dependence and loss of joint strength occurred only some time after all the gold had been converted.MST/1599b

Reaction processes between silver or zinc doped Pb–Sn solder and gold

AbstractThe microstructures of soldered joints made on gold using silver or zinc doped Pb–Sn solder have been studied in the scanning electron microscope before and after accelerated aging. Layers of Au–Sn intermetallic compounds form between the unreacted gold and the solder as a result of the diffusion of gold through the product layers. The reaction kinetics has been studied as a function of temperature for the silver doped system and, in the initial stages, was found to be parabolic with an activation energy of (0·86±0·03) eV. This is the same as for joints made using undoped Pb–Sn solder. As in the undoped system, the growth of the product layers subsequently fell below the t1/2 dependence and loss of joint strength occurred only some time after all the gold had been converted.MST/1599b

Au-Sn金属間化合物のメスバウアー効果

119Sn Mössbauer spectra of Au-Sn binary alloys with different tin concentrations from 2 to 90 at%Sn have been measured. The obtained values of the isomer shift (ΔSI) and the quadrupole splitting (ΔEQ) for four Au-Sn intermetallic compounds, ζ, AuSn, AuSn2 and AuSn4, were discussed by taking account of their crystal structures. The values of isomer shift for these compounds relative to BaSnO3 at room temperature were 2.02(3), 2.28(2), 2.35(2) and 2.73(6), respectively. They increased almost linearly with the tin concentration except that the value of AuSn4 showed a large deviation beyond that of β-Sn. The result was well explained in terms of two characteristic features in the compounds, i.e. the number of Au near-neighbours for Sn atoms, nAu, and the specific volume of Sn atoms, VSn. The quadrupole splittings for the four compounds were 0.25(2), 0.25(2), 0.71(2) and 0.17(3), respectively. They were of the same order as that of β-Sn, except a larger splitting for AuSn2. These values well agreed with a simplified calculation of electric field gradient at a Sn site surrounded by near-neighbour Au atoms which were assumed to be point charges. The spectrum of AuSn2 was resolved into two doublets, which suggested a large difference in electronic configurations between two sorts of lattice sites of tin atoms.

Room temperature interdiffusion studies of Au/Sn thin film couples

Room temperature interdiffusion studies of Au/Sn thin film couples were made using transmission electron microscopy, X-ray diffraction and Rutherford backscattering techniques. Au/Sn thin film couples were found to interdiffuse at room temperature via both bulk and grain boundary diffusion mechanisms. In the bulk diffusion, gold diffuses interstitially into tin and initially forms AuSn 4 and AuSn intermetallic compounds. Grain boundary diffusion of tin into gold is also observed. The use of various thickness combinations in the thin film couples permitted detection of four intermetallics (ζ phase, AuSn, AuSn 2 and AuSn 4) which can form as a result of the interdiffusion. In addition, it was found that interdiffusion accompanied by the formation of hillocks and Kirkendall voids.

Thermal analysis of single-crystal silicon ribbon growth processes : A. E. Bell. RCA Review38, 109 (March 1977)

Formation of AuSnx intermetallic compounds (IMCs) in laser reflowed solder joints was investigated. The results showed that few IMCs formed at the solder/0.1 μm Au interface. Needlelike AuSn4 IMCs were observed at the solder/0.5 μm Au interface. In Sn-2.0Ag-0.75Cu-3.0Bi and Sn-3.5Ag-0.75Cu solder joints, when the laser input energy was increased, AuSn4 IMCs changed from a layer to needlelike or dendritic distribution at the solder/0.9 μm Au interface. As for the solder joints with 4.0 μm thickness of Au surface finish on pads, AuSn4, AuSn2, AuSn IMCs, and Au2Sn phases formed at the interface. Moreover, the content of AuSnx IMCs, such as, AuSn4 and AuSn2, which contained high Sn concentration, would become larger as the laser input energy increased. In the Sn-37Pb solder joints with 0.9 μm or 4.0 μm thickness of the Au surface finish on pads, AuSn4 IMCs were in netlike distribution. The interspaces between them were filled with Pb-rich phases.

Graphical analysis of accelerated life test data with a mix of failure modes : Wayne Nelson. IEEE Trans. Reliab.R-24 (4), 230 (1975)

An experimental investigation was combined with a non-linear finite element analysis using an elastic–viscoplastic constitutive model to study the effect of ball shear speed on the shear forces of BGA solder joints. Two solder compositions were examined in this work: Sn–3.5Ag and Sn–3.5Ag–0.75Cu. The Cu substrates had been surface finished electrolytically with a 7 μm thick Ni diffusion barrier followed by an 0.5 μm thick Au layer to enhance solderability. Ag3Sn and a few AuSn4 intermetallic compound (IMC) particles were found inside the two solders. Only a continuous Ni3Sn4 layer was observed at the interface between the Au/Ni plated layer and the Sn–3.5Ag, while a continuous (Ni1−xCux)3Sn4 layer and a small amount of discontinuous (Cu1−yNiy)6Sn5 particles were formed at the interface between the substrate and the Sn–3.5Ag–0.75Cu. The IMC was identified using energy dispersive spectrometer (EDS) and electron probe micro analysis (EPMA). Shear tests were carried out over a shear speed range from 10 to 700 μm/s at a shear ram height of 50 μm. The shear force was observed to linearly increase with shear speed and reach a maximum value at the highest shear speed in both the experimental and the computational results. All test specimens fractured in a ductile mode. The failure mechanisms were discussed in terms of von Mises stresses and plastic strain energy density distributions.