Au-Sn Alloy Research Articles

Solder metallization interdiffusion in microelectronic interconnects

We investigated the growth of intermetallic compounds in Cu/Ni/Au/PbSn solder joints. The substrates that we investigated had been Au plated by one of two different techniques. The Au finish thicknesses ranged from 0.25 to 2.6 /spl mu/m. After solder renew, structural examinations using optical and electron microscopy of cross-sectioned solder joints revealed the growth of Ni/sub 3/Sn/sub 4/ at the solder/Ni interface after reflow. Solder joints with thicker layers of Au annealed in Ar gas at a temperature of 150/spl deg/C for up to 450 h, displayed an appreciable growth of Au/sub 0.5/Ni/sub 0.5/Sn/sub 4/ at the Ni/sub 3/Sn/sub 4//solder interface. Previous investigators correlated growth of a Au-Sn alloy with the degradation of the mechanical properties of the solder joint. The determination of the stoichiometry of the Au/sub 0.5/Ni/sub 0.5/Sn/sub 4/ phase provides some understanding of why this phase grew at the Ni/sub 3/Sn/sub 4//solder interface, as Sn, Au and Ni are all readily available at this interface. The growth of this ternary alloy is also consistent with trends observed in the kinetics of formation of solder alloys.

Spontaneous alloying of tin atoms into nanometer-sized gold clusters and phase stability in the resultant alloy clusters

Alloying behavior and phase stability has been studied in situ by transmission electron microscopy using clusters in the Au-Sn system. When tin atoms are vapor-deposited onto nm-sized gold clusters, rapid dissolution of tin atoms into gold clusters takes place and as a result Au-rich solid solution, amorphous-like Au-Sn alloy and AuSn compound clusters are formed depending upon the concentration of tin. The remarkable enhancement of solubility has been observed in Au-rich solid solution and AuSn compound. It becomes more difficult to form two phases in the interior of individual clusters even if the composition of alloy clusters falls in the two-phase region in the phase diagram for the bulk alloy and as a result amorphous-like phase is stabilized in nm-sized Au-Sn alloy clusters.

A novel GaAs flip-chip power MODFET with high gain and efficiency

A novel GaAs flip-chip power MODFET with a spike-gate structure has been developed for high-gain and high-efficiency operation under extremely low supply voltages. The spike-gate MODFET is featured by a unique gate structure that has almost zero effective gate length. The spike gate provides both a low on-resistance of 1.5 Ω mm and a high transconductance of 280 mS/mm without increasing the drain conductance. The flip-chip bonding, with an Au–Sn alloy system, has been used for mounting of the spike-gate power MODFET on an AlN substrate. The thermal resistance of the flip-chip power MODFET is 12°C/W which is lower than that of a conventional wire-bonded MODFET. The power-added efficiency (PAE) of 71% at the output power of 30.0 dBm can be obtained even when the supply voltage is reduced to 1.5 V. By eliminating parasitic wire inductance, the linear gain of the MODFET is 2 dB higher and the PAE is 5% higher than that of the conventional wire-bonded MODFET.

Ａｕ‐Ｓｎ合金はんだによるフラックスレス薄板積層接合

Ａｕ‐Ｓｎ合金はんだによるフラックスレス薄板積層接合

A new bonding technique for microwave devices

Over the past five years, a great deal of work has been done to perform semiconductor die attach with AuSn alloys. Successful die attach has recently been achieved using Au and Sn multilayers evaporated onto the die or the host substrate. However, bonding techniques with thin (below 5 /spl mu/m) AuSn layers for very thin semiconductor devices have not yet been reported. The increasing demand for more advanced optoelectronic integrated circuits has created the need to bond materials having different lattice constants (e.g., GaAs on Si). In this paper we report a new way for the bonding of epitaxial liftoff (ELO) devices onto host substrates. Three of the multilayer structures investigated in this work produce a AuSn alloy bond with approximately 84 wt.% gold, but can be bonded with a peak temperature below 280/spl deg/C. The bonded samples were investigated with several standard surface analysis techniques: Optical microscopy, scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX). We conclude that much thinner bonding layers can be attained than thus far reported. The results of our research allow us to optimize the layer structure and bonding parameters.

Low temperature bonding of epitaxial lift off devices with AuSn

The increasing demand for more advanced optoelectronic integrated circuits has created the need for bonding materials with different lattice constants (for example, GaAs on Si). In this paper, we report a new way for the bonding of epitaxial lift off (ELO) devices onto substrates. The multilayer structures investigated in this work produce a resulting AuSn alloy with approximately 84 wt.% gold, but can be bonded with a peak temperature of 235/spl deg/C. The bonded samples were investigated with several standard surface analysis techniques like optical microscopy, scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX) as well as mechanical tests. The results of our research allowed us to optimize the layer structure, the bonding parameters as well as the diffusion barriers.

An analysis of the specific heat capacity of liquid Au-Sn alloy based on the ideal-associated solution model

The specific heat capacity of Au Sn liquid alloy was analyzed using the ideal associated solution model assuming associated compounds Au,Sn, AuSn, and AuSn2. Based on this model, all of the specific heat capacity. heat of mixing and activity are described over a wide temperature range, Further, it became clear that (he summation of mole numbers of the species in the liquid alloy shows a minium at the stoichiometric composition of Au3Sn, which implies that the liquid is the most ordered at this composition,

Recording Characteristics and Reliability of Novel Writable Compact Disc Using a Au-Sn Alloy Single Layer

We have developed a novel writable compact disc (CD) using a Au70Sn30 alloy recording film. This has the advantages of a single-layered, simple structure suitable for conventional CD processes, high reflectivity, low toxicity and high reliability. Recording marks are formed by filling up the grooves resulting from thermal deformation and deconstruction of polycarbonate resin. Modulation amplitudes of 0.37 (3 T) and 0.87 (11 T) are obtained by this new recording method. The addition of Ti to the recording film improves its reliability by preventing Sn oxidization.

Au-Sn bonding metallurgy of TAB contacts and its influence on the Kirkendall effect in the ternary Cu-Au-Sn

The authors summarize work done on different Au-Sn-Cu and Au-Cu metallurgies in the inner lead bond (ILB) area. The influence of Kirkendall-pore formation in the Cu-Au-Sn system as a degradation mechanism is shown. This effect together with the formation of a new type of ternary intermetallic compound is observed during thermal aging in contacts with a direct interface between the eutectic 80/20 Au-Sn alloy and copper. The zeta-phase (Au/Sn 90/10) acts like a diffusion barrier, which inhibits the pore formation associated with copper diffusion. The composition of the ternary intermetallic compounds, their growth constant, and their activation energy were determined. The possibility of increasing the contact reliability by producing a reliable Au-Sn metallurgy during the ILB-process is shown. >

AuSn alloy phase diagram and properties related to its use as a bonding medium

AuSn eutectic alloy has been successfully used in microelectronic packaging for high reliability applications where a hard solder as well as a low processing temperature are required. A new multilayer bonding technology not only has produced nearly perfect bonding but also has reduced the processing temperature even below the eutectic melting point. Knowledge of the different phases of the alloy and their formation, as well as the interdiffusion that occurs, thus becomes important in studying the bonding principle and the long-term reliability. In this paper, we review a large number of publications on the AuSn system and summarize the important properties. We hope that this summary would further enhance the development of new AuSn bonding methods as a result of an overall understanding of oxidation and diffusion properties.

Adsorption of metallic tin on the Au(111) surface

The growth mode of metallic Sn deposited onto the Au(111) surface has been investigated using Auger electron spectroscopy, low-energy electron diffraction, electron-energy-loss spectroscopy and work-function measurements for deposition at room temperature and at low temperature (−70 to −100 °C). At room temperature, Sn initially forms an alloy, AuSn, which grows laterally as a double layer, followed by continued growth of the same alloy one layer at a time. This differs from the situation for Pb and Bi on Au(111), which form an overlayer on Au before alloying. However, Sn deposited at low temperature does appear to form one layer of pure Sn followed by the growth of the AuSn alloy underneath. This latter conclusion is different from that of a previous study which suggested that Sn forms one layer of AuSn alloy covered by pure Sn layers at low temperature. The difference may be caused by different deposition rates.

Void free bonding of large silicon dice using gold-tin alloys

The successful bonding of large (6 mm*10 mm) silicon dice on alumina substrates with Au-Sn eutectic using a particular bonding technique is described. The bonding quality was examined by a scanning acoustic microscope having a resolution of 25 mu m and it was found that nearly perfect bondings have been achieved. Use of Au-Sn alloy rather than Au-Si resulted in not only lower processing temperature but also lower stress on the dice. This is confirmed by simple stress analysis. The die-bonded specimens endured 40 cycles of thermal shock between -196 degrees C (liquid nitrogen) and +160 degrees C (boiling cyclohexanol) without cracking or bond degradation despite the significant mismatch of thermal expansion coefficients between silicon and alumina. Storage tests at -196 and 250 degrees C also do not induce cracking or bond degradation. Pull test results indicate that the bondings are stronger than the silicon dice themselves.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Highly reliable die attachment on polished GaAs surfaces using gold-tin eutectic alloy

GaAs test dice with polished surfaces were successfully bonded on alumina substrates using Au-Sn alloy. The bonding process was carried out in H/sub 2/ or N/sub 2/ atmosphere with applied static pressure, but without the use of scrubbing. The quality of the bonds was examined by a scanning acoustic microscope (SAM) having a spatial resolution of 25 mu m. After 100 cycles of thermal shock between -196 degrees C to +160 degrees C, perfectly bonded devices remained perfect, as confirmed by the SAM images. No void was induced, and the dice did not crack. The results of a shear test indicate that the strength of the bondings is greater than that of the GaAs dice.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Failure Modes of InGaAsP/InP Lasers Due to Adhesives

Sudden failure modes for lnGaAsP/InP lasers were observed during aging. Growth of Sn whiskers, formation of voids between the heat sink and package stem, separation of metallized metal from the diamond heat sink, and reaction of solder material with laser chip were observed. Since they were found to induce sudden failures, the choice of bonding solders and metals for heat sink metallization is very important to obtain highly reliable lasers. A Au-rich Au-Sn alloy was found to be the most stable solder against the sudden failures among Sn, Sn-rich Au-Sn, Pb-Sn, and Au-rich Au-Sn.

電析Ａｕ‐Ｓｎ，Ａｇ‐Ｓｎ合金の微細構造と相について

The microstructure and the phase of Au-Sn and Ag-Sn alloys electrodeposited from cyanide baths were investigated by X-ray diffraction and transmission electron microscopy. On the solubility of α solid solution and the range of intermediate phase ζ Au-Sn and ζ Ag-Sn of the electrodeposited Au-Sn and Ag-Sn alloys in room temperature, the solubility was decreased and the range was shifted to Sn side by about 10at% as alloy composition in comparison with the thermally equilibrium alloys. The intermetallic compounds of AuSn, AuSn2, and AuSn4 were electrodeposited, but the superlattice ε phase in the Ag-Sn alloy was not formed. In both of electrodeposited Au-Sn and Ag-Sn alloys, coring structure by peritectic reaction could not be observed, instead, the homogeneously mixed structure consisting of α and ζ phase was observed. These α and ζ crystallites grew epitaxially with substrates, and no specific habit relationship between α and ζ crystallites was found. The morphology of the crystallites was also influenced by substrates; that is the slender ζ-crystallites in the Au-Sn alloy deposited on the (011) Cu substrate were elongated in the [011] Cu substrate direction. This phenomenon was caused by misfit between (200) Cu and (0111) ζ plane along the [100] Cu direction.

The surface composition of Au–Sn alloys determined by Auger electron spectroscopy

The Auger spectra of clean and equilibrated Au–Sn alloy ingots of bulk composition ranging between 50 and 99 at% Au have been obtained. The intensity ratios of Auger peaks of various different energies were normalized by comparison with the corresponding intensity ratios from pure Au and Sn. The normalized intensity ratios are used to obtain the surface atom fractions by applying a model which takes full account of the attenuation of the Auger electrons. It is found that for a one phase alloy with overall composition of 50 at% Au there is little or no segregation at the surface, while for a one phase alloy with bulk composition of 86 at% Au there is marked segregation of Sn (surface monolayer composition of about 43 at% Au). For the alloys of bulk compositions between 50 and 86 at% Au in which both phases are present, the surface composition is given by applying the lever rule to the one phase surface compositions. For 1 at% Sn dissolved in the Au lattice there is also considerable enrichment of the surface with Sn (surface monolayer composition of about 46 at% Au). These surface compositions are related to the properties of the bulk phase diagram and are explained by the interplay of the differences in atomic size and in heats of sublimation of pure Au and Sn and of the heats of mixing of the alloys.

Ａｕ系共晶合金を用いた薄膜溶融接合について

As for diamond heat sinks, the properties of Au eutectic alloys used for bonding a semiconductor chip to a diamond are investigated, and then, film-soldering method is studied in which a semiconductor chip is soldered to a metallized diamond substrate evenly under small load with low melting alloyed film.As soldering materials, Au-Sb, Au-Sn and Au-In alloys are selected and their properties, viz. thermal conductivity, electric resistance, hardness and tensile strength, are investigated. In all alloys, their eutectic alloys have similar properties, and in Au-Sb alloy, which has no alloy phase in hypo-eutectic region, it can improve its properties when its composition becomes Au-rich from the eutectic composition.In soldering experiments, Au-Sb alloy is mainly used and GaAs chips and Pyrex glass, as model specimens, are soldered in an atmosphere of H2 gas. The effects of temperature, time, load, film thickness, film structure, and film composition on the soldering strength are investigated, resulting that the conditions for assuring the appropriate soldering are defined. From the XMA analysis of alloyed film's composition, together with above results, it is found that the rate of soldering reaction is controlled by the interdiffusion of Sb into Au solid phase.In comparison with above results, similar investigation is carried out using Au-Sn alloy.

Electronic Behavior in Alloys: Au-Sn

Charge-flow and valence-$d$-band behavior in Au alloys have been studied in the Au-Sn alloy system by x-ray photoemission measurement of the valence bands and of core-level energy shifts for both atomic species. Published M\ossbauer isomer-shift data for these alloys indicate that there is significant valence charge increase at Au sites and a somewhat smaller decrease at Sn sites upon alloying. An analysis, which includes screening in the Coulomb interactions between valence and core electrons and which combines the M\ossbauer and core-level photoemission data, has been carried out. The results indicate that there is little net charge flow between Au and Sn, i.e., that the increase of non-$d$ conduction-electron count at Au sites is almost entirely compensated for by a decrease in $5d$ count; a similar $s\ensuremath{-}p$ compensation occurs at Sn sites. Coulomb screening is important to this analysis and we have applied it to similar results reported by us previously in the AuAg alloy system. Substantial hybridization of the Au $d$ bands with the Au $s$ and with Sn valence-electron states is exhibited by the valence-band spectra; and the extent of this hybridization with final states above the Fermi level is indicated by the observed depletion in $d$ count.

Atomic Distributions and Electrical Resistivities of Liquid Gold-Tin Alloys

The distributions ρij(r) of Au-Au, Sn-Sn and Au-Sn pairs have been calculated using the three partial interference functions Iij(K ) which were evaluated from the scattered x-ray intensities of liquid Au-Sn alloys measured by Kaplow, Strong and Averbach. The functions IAuAu (K) and ISnSn(K) and their corresponding Fourier transforms are similar to those observed in their respective pure liquids. The functions IAuSn ( K ) and ρAuSn(r) resemble closely a model structure based on a solid AuSn alloy with a NiAs-type structure. The electrical resistivities of the alloys obtained with Iij(K ) and the pseudo-potential elements Ui(K) show a large increase upon alloying Sn into Au in agreement with experimental observation.

Partial interference functions of liquid gold-tin alloys

Three partial interference functions Iij( K) which describe the distributions ϱij( r) of Au-Au, Sn-Sn and Au-Sn pairs in reciprocal space have been calculated from the scattered X-ray intensities of liquid Au-Sn alloys which were measured by Kaplow et al. Assuming that the Iij( K) are independect of the relative abundance of the elements in the alloys, a least square analysis yielded I AuAu ( K) and I SnSn ( K) which are very similar to those observed in their respective pure liquids, whereas I AuSn ( K) resembles closely that obtained from a model structure based on a solid AuSn alloy with NiAs-type structure.