AuSn4 Phases Research Articles

Vacuum brazing of medical TA9 alloy to ZrO2 bioceramics using a biocompatible filler: Interfacial microstructure, mechanical properties and biocompatibility

Based on the principle of developing new biocompatible fillers, the Sn–Zr + AuSn20 filler system was designed. Firstly, the surface of ZrO2 ceramics was metallized by biocompatible Sn-xZr filler at 900 °C for 20 min. The interfacial microstructure of the Sn–Zr metallization layer/ZrO2 consisted of β-Sn + Sn2Zr/m-ZrO2/t-ZrO2. Then the pre-metallized ZrO2 ceramics were brazed to TA9 alloys by AuSn20 metal foil at 550 °C for 30 min. The typical interfacial microstructure of the TA9/ZrO2 joint is TA9/AuTi5Sn3+Sn–Zr/AuSn4+AuSn2+Au–Sn–Zr + ZrSn2/AuSn4+m-ZrO2/t-ZrO2. With the increase of Zr content, the Sn2Zr phase gradually increases in the metallized layer, the thickness of the AuTi5Sn3 layer decreases, the AuSn4 phase gradually decreases, and the AuSn2 phase gradually increases in the TA9/ZrO2 joint. Besides, the optimal shear strength of 46.5 MPa is obtained at 550 °C for 30 min with 6 at.% Zr content. At this point, the joint fractures at the interface of the AuTi5Sn3 and AuSn4 layers, which is a weak area of the joint. Only a little amount of m-ZrO2 is changed from t-ZrO2 inside the t-ZrO2 substrate; the majority of m-ZrO2 grows directly on the t-ZrO2 substrate surface. All materials have no cytotoxicity, and even the Sn–Zr metallization layer can promote cell proliferation.

Low temperature brazing between pre-metallized ZrO2 ceramics and medical pure titanium using AuSn20 filler metal

ZrO2 ceramic was metallized by Sn-xTi (x = 2, 3 and 4 at.%) foils at 1000 °C for 30 min. As the Ti content was 3%, the continuous and homogeneously distributed Ti–O compounds layer formed at the interface. The metallization layer metallized Sn–3Ti foil consisted of Ti2O3 layer + Ti11.31Sn3O10/β-Sn + Ti2Sn3+Ti6Sn5. During the metallization process, as the thickness of metallization layer increased, the Ti–O and Ti–Sn–O layers became continuous, Ti2Sn3 and Ti6Sn5 phases increased and aggregated obviously. Vacuum brazing using AuSn20 filler metal after pre-metallization were utilized to achieve the robust ZrO2/Sn–3Ti/AuSn20/Ti joints. The effect of the metallization layer thickness on microstructure and mechanical properties was systematically examined. The typical interfacial microstructure of ZrO2/Sn–3Ti/AuSn20/Ti joints brazed at 550 °C for 30 min was ZrO2/Ti2O3+Ti11.31Sn3O10/β-Sn + Ti6Sn5+AuSn2+AuSn4+AuTi5Sn3 layer/Ti. During brazing process, the Ti–O and Ti–Sn–O layers beside ZrO2 ceramic varied barely with the increasing of the thickness of metallization layer during brazing process. In the brazing seam, the AuSn2 phases and Ti6Sn5 phases attenuated whereas AuSn4 phases evidently increased with the thicker metallization layer. The AuTi5Sn3 layer nearby the Ti substrate thickened significantly varied with the thickness of metallization layer. Additionally, the ZrO2/Ti brazed joint with the maximum shear strength of 48.6 MPa was achieved by the metallization layer thickness of 150 μm. Furthermore, fracture analysis demonstrated that the cracks initiated at the Ti–O layer and propagated along the AuSn2 phases and layered Au–Ti–Sn phases.

Investigation of phase equilibria of the Au–Ni–Sn ternary system and interfacial reactions in the Au/Sn/Ni/Cu multilayer couple

Au and Ni are widely used in the under-bump metallization, whereas Sn and Cu serve as common bonding materials and substrates, respectively. Solder joints consisting of an Au/Sn/Ni/Cu multilayer structure are widely found in the electronic packaging. Both phase equilibria of the Au–Ni–Sn ternary alloys and interfacial reactions of the Au/Sn/Ni/Cu multilayer structure were applied to the solid/solid-state reaction couple technique. The results showed that the Ni3Sn2 and AuSn4 phases respectively had a great solubility of the third element and the ternary AuNi2Sn4 phase existing in the Au–Ni–Sn ternary alloys was formed at 180 and 240 °C. The Sn/Ni/Cu multilayer structure was prepared by electroplating Sn/Ni layers on the Cu substrate. Afterward, the Sn/Ni/Cu multilayer and Au foil were screwed together to obtain the Au/Sn/Ni/Cu multilayer structure, followed by reactions at 150, 180 and 200 °C for different durations. The thickness of the intermetallic compounds (IMCs) increased with the increase in the reaction time and temperature. The IMC evolution in the couple remained unchanged at different temperatures. An increase in the reaction time converted the AuSn4 and AuSn2 phases to the AuSn phase. The voids formed in the couple were attributed to the volume shrinkage effect, which decreased with an increase in the reaction temperature. The (Ni, Au)3Sn2 phase was formed at the Ni side; the Ni layer functioned as an effective diffusion barrier to prevent the formation of the Cu–Sn IMCs.

The Effect of Laser Energy and Nitrogen Flow in Solder Joints Properties of Head Gimbal Assembly

The objective of this research is to study the effect of laser energy and Nitrogen flow on the solder joints of the Head Gimbal Assembly (HGA). The soldering of the HGA components isn’t the same as general semiconductors. Since the soldering figure perpendicular to each other so that, it was used the laser solder jet bonding system. The solder jet bonding system uses a solder ball consisting of Sn-2.0Ag-0.7Cu (SAC207) is used for connection of the HGA pad made from a Cu trace coated with Au. The growth of intermetallic compounds (IMCs) and shear strength will be analyzed to investigate the effects of laser energy and Nitrogen flow on solder joint reliability. In this research, laser energy levels since 2, 2.5, 3, 3.5, 4, and 4.5 mJ and keep the Nitrogen flow value at 90 mbar. As for the Nitrogen flow effect analysis, the Nitrogen flow level was used at 80, 100, 120, and 140 mbar and keep the laser energy value 3.5 mJ. The results of the study show that the increased levels of laser energy can inhibit the growth of intermetallic compounds as well as the AuSn4 phase that can present benefit to solder joints with results showing within the shear strength to increase significantly. The increase in Nitrogen flow levels has the same effect as the increase in laser energy levels, which can decreases the growth of intermetallic compounds and AuSn4 phase also including increased shear strength. The difference between laser energy and Nitrogen flow increasing shows the level of laser energy can clearly distinct the effect on each level. But the increase in Nitrogen flow level is statistically insignificant from each level.

Solid–state diffusion–controlled growth of the phases in the Au–Sn system

The solid state diffusion-controlled growth of the phases is studied for the Au–Sn system in the range of room temperature to 200 °C using bulk and electroplated diffusion couples. The number of product phases in the interdiffusion zone decreases with the decrease in annealing temperature. These phases grow with significantly high rates even at the room temperature. The growth rate of the AuSn4 phase is observed to be higher in the case of electroplated diffusion couple because of the relatively small grains and hence high contribution of the grain boundary diffusion when compared to the bulk diffusion couple. The diffraction pattern analysis indicates the same equilibrium crystal structure of the phases in these two types of diffusion couples. The analysis in the AuSn4 phase relating the estimated tracer diffusion coefficients with grain size, crystal structure, the homologous temperature of experiments and the concept of the sublattice diffusion mechanism in the intermetallic compounds indicate that Au diffuses mainly via the grain boundaries, whereas Sn diffuses via both the grain boundaries and the lattice.

Interfacial reactions in the Au/Sn-xZn/Cu sandwich couples

Abstract The interfacial reactions in the Au/Sn-Zn/Cu sandwich couples were investigated. The Sn-xZn/Cu couples were reflowed at 270 °C for 1 h and then clamped together over an Au foil. These Au/Sn-Zn/Cu sandwich couples were aged at 160 °C for various periods of time. The AuSn, AuSn2, and AuSn4 phases were formed at the Sn-1Zn/Au interface when the Au/Sn-1 wt% Zn/Cu sandwich couple was aged for 20 h, the Cu6Sn5 phase was also observed between Au-Sn intermetallic compounds (IMCs) and solder. This result revealed that Cu atoms rapidly diffused through the Sn-1Zn solder to form Cu-Zn IMC on the Au side. The Au-Sn IMCs, Au-Zn IMCs, and an Au-Sn-Zn ternary metastable phase were formed at the interface in the Sn-5Zn/Au and Sn-9 wt% Zn/Au couple. When Zn contents were more than 20 wt%, only the Au-Zn IMCs, AuZn, Au3Zn7, and AuZn3 phase were formed at the Sn-xZn/Au interface. On the Cu side, when the Sn-Zn/Cu couple was reflowed at 270 °C for 1 h, the result indicated that the (Cu, Zn)6Sn5, (Cu, Sn)Zn phases were found at the Sn-1 wt.% Zn/Cu interface, the Cu5Zn8 phase was found at the Sn-5Zn/Cu interface and the (Cu, Sn)5Zn8, (Cu, Sn)Zn5 phases were found at the Sn-xZn/Cu interfaces (x = 9, 20 and 40 wt%). After 1000-h aging, the CuZn and Cu6Sn5 phases were formed at the Sn-1Zn/Cu interface, and only the Cu5Zn8 phase was observed at the Sn-(5 to 40) wt% Zn/Cu interfaces. The results indicated that no Au-Cu ordered phases were observed at both Au and Cu sides, and IMC formation in the Au/(Sn-xZn)/Cu sandwich couple strongly depended on the Zn concentration effect in the Sn-xZn alloys.

Thermal Management and Interfacial Properties in High-Power GaN-Based Light-Emitting Diodes Employing Diamond-Added Sn-3 wt.%Ag-0.5 wt.%Cu Solder as a Die-Attach Material

The thermal management of high-power GaN-based light-emitting diodes (LEDs) soldered with Sn-3 wt.%Ag-0.5 wt.%Cu (SAC305) solder and diamond-added SAC305 solder was evaluated. Diamond addition was found to significantly reduce the surface temperature and total thermal resistance of the LEDs, revealing that diamond-added SAC305 solder is a promising die-attach material for high-power LED packaging. Interfacial reactions in the LED solder joints were also investigated. The thin Au wetting layer in the chip’s backside metallization was rapidly consumed in the initial stage of reflow, forming an AuSn4 phase at the interface. Subsequently, the AuSn4 phase detached from the interface, leading to dewetting of the SAC305 solder from the LED chip. To avoid dewetting, a new backside metallization of LED chips should be developed for SAC305 solder.

Comments on “Room temperature interfacial reactions in electrodeposited Au/Sn couples”

Recently, Tang et al. (Acta Mater. 56 (2008) 5818) published a paper explaining room temperature growth of the phases in the Au/Sn system. In their analysis, they considered Au as the only mobile species for all the product phases, and Sn as virtually immobile. It is shown here that this analysis is not correct, since Sn has a higher diffusion rate through the AuSn4 phase. On the other hand, the mobilities of species in the AuSn2 phase are as yet unknown.

Investigation of the Phase Equilibria of Sn-Cu-Au Ternary and Ag-Sn-Cu-Au Quaternary Systems and Interfacial Reactions in Sn-Cu/Au Couples

The phase equilibria of the Sn-Cu-Au ternary, Ag-Sn-Cu-Au quaternary systems and interfacial reactions between Sn-Cu alloys and Au were experimentally investigated at specific temperatures in this study. The experimental results indicated that there existed three ternary intermetallic compounds (IMCs) and a complete solid solubility between AuSn and Cu6Sn5 phases in the Sn-Cu-Au ternary system at 200°C. No quaternary IMC was found in the isoplethal section of the Ag-Sn-Cu-Au quaternary system. Three IMCs, AuSn, AuSn2, and AuSn4, were found in all couples. The same three IMCs and (Au,Cu)Sn/(Cu,Au)6Sn5 phases were found in all Sn-Cu/Au couples. The thickness of these reaction layers increased with increasing temperature and time. The mechanism of IMC growth can be described by using the parabolic law. In addition, when the reaction time was extended and the Cu content of the alloy was increased, the AuSn4 phase disappeared gradually. The (Au, Cu)Sn and (Cu,Au)6Sn5 layers played roles as diffusion barriers against Sn in Sn-Cu/Au reaction couple systems.

Effects of substrate metallizations on solder/underbump metallization interfacial reactions in flip-chip packages during thermal aging

Effects of Ni and Au from Ni/Au substrate metallizations on the interfacial reactions of solder joints in flip-chip packages during long-term thermal aging were systematically investigated. It was found that both Au and Ni influenced the solid-state interfacial reactions, underbump metallization (UBM), and intermetallic compound (IMC) evolution. Because large amounts of Ni could incorporate into IMC to form a multicomponent (Cu, Ni)6Sn5 phase during assembly reflow, while Au could only affect the reaction during thermal aging through the reconfiguration of AuSn4 phase, Ni had stronger effects on solid-solution type Ni–V UBM consumption than Au. It was found that the UBM consumption process was faster in the eutectic SnPb solder system than that in the SnAgCu solder system during aging. A porous structure was formed in the UBM layer after Ni in UBM was consumed. Electrical resistance of flip-chip packages increased significantly after the porous structure reached certain extents. The results showed that the diffusion process of Ni from UBM and Sn from solder in the presence of (Cu, Ni)6Sn5 or (Ni, Cu)3Sn4 phase at solder joint interfaces could be much faster than that in the case of binary Cu6Sn5 or Ni3Sn4 IMC.

Au−Ni−Sn intermetallic phase relationships in eutectic Pb−Sn solder formed on Ni/Au metallization

Recent work has shown that a Au−Ni−Sn ternary compound with a nominal composition of Au0.5Ni0.5Sn4 redeposits and grows at the interface between eutectic Pb−Sn solder and Ni/Au metallization during aging at 150°C. The present work verifies the existence of the Au0.5Ni0.5Sn4 phase by examining the Sn-rich corner of the Au−Ni−Sn ternary phase diagram. The reconfiguration mechanism of the AuSn4 from the bulk solder is also discussed, with detailed observations of the Au0.5Ni0.5Sn4 microstructure. The results show that the Ni solubility limit in the AuSn4 phase is approximately 12 at.% at 150°C and thus, the Au0.5Ni0.5Sn4 phase is a ternary AuSn4-based compound with high Ni solubility. Due to the slight solubility and the fast diffusion of Au in the eutectic Pb−Sn at 150°C, the AuSn4 intermetallics in the bulk solder can reconfigure to form a AuxNi1−xSn4 compound at the interface where Ni is available. The AuxNi1−xSn4 compound layer consists of nanocrystals arranged in a larger grainlike morphology. It appears that the inherent lattice strain of the AuxNi1−xSn4 compound and the volume change due to its formation results in a nanocrystalline microstructure.