AuSn Solder Research Articles

Reliability Simulation of IGBT Module with Different Solders Based on the Finite Element Method

The interconnecting solder is a key control factor for the reliability of electronic power packaging because it highly affects the junction temperature of insulated-gate bipolar transistor (IGBT) modules and is prone to plasticity, creep, and other failure behaviors under temperature-change environments. In this paper, the interconnecting performance and fatigue life of five different kinds of solders such as SAC305, sintered silver, Au80Sn20, sintered copper, and pure In under direct current (DC), power cycle, and electro-thermal coupling complex environments were studied based on electro-thermal multi-physical field coupling finite element simulation method, respectively. Results show that the sintered silver owns the most outstanding thermal reliability and the DC operating junction temperature of the IGBT module after utilizing sintered silver solder is only 90.2 °C, which is nearly 15 °C lower than that of the IGBT module utilizing SAC305 solder. Furthermore, in the power cycle reliability test, the fatigue life of Au80Sn20 solder reaches a maximum of 3.26 × 107 cycles while the life of indium presents only 5.85 × 103 cycles, a difference of nearly four orders of magnitude. Finally, under the complex environment of electro-thermal coupling, the fatigue life of Au80Sn20 solder is also the largest at 1.9 × 106 cycles, while the smallest life of solder becomes SAC305 solder at 4.44 × 102 cycles. The results of this paper can provide a theoretical basis for solder selection and life prediction of the IGBT module, which is of great significance in improving the reliability of power electronic packaging.

Elemental composition optimization to achieve eutectic Au–Sn solder

Elemental composition optimization to achieve eutectic Au–Sn solder

Dual-cluster interpretation of Au–Sn binary eutectics and solders

Au–Sn alloy is an important high-temperature solder, but it has some disadvantages such as high cost and brittleness. Multicomponent alloying is often performed to improve performance and reduce their cost. However, due to the absence of an atomic structure model, there has been a lack of effective theory to guide their composition design. Since Au–Sn solders are typically eutectic-based, understanding the Au–Sn eutectic at the atomic level is of great significance for clarifying the composition origin of Au–Sn solders and the subsequent multi-component composition design. In the present work, the short-range order of Au–Sn eutectics is characterized using a dual-cluster model. In the dual-cluster formulism, the two eutectics Au69.6Sn30.3 and Sn94.6Au5.4 at. % are interpreted in terms of the hypoeutectic [SnAu12]Sn2Au3 + [Au–Au2Sn6]Au3 = Au70.0Sn30.0 and [Au–Sn8]Au1 + 2{[Sn–Sn10]Sn5} = Sn95.2Au4.8 alloys, respectively. The compositions of Au–Sn solders are then analyzed based on the interpreted dual-cluster formulas, which indicate that the number of atoms of the alloying elements that replace the atoms in the dual-cluster formulas is always an integer. The present method provides a quantitative approach toward developing a practical composition interpretation and design tool for Au–Sn-based solders.

Research on Processability and Transmission Performance of Low Temperature Co-Fired Ceramic Ball Grid Array Packaging Based on Electroless Plating Surface Modification for Microwave Transceiver Circuits.

A microwave transmitter/receiver using the low-temperature co-fired ceramic substrate and ball grid array packaging demonstrates superior properties, including high integration, miniaturization, and high electromagnetic shielding. However, it holds limitations of inadequate hermeticity (that is, gas or moist impermeability), high cost, and low reproducibility. In this work, we aim to overcome these difficulties by introducing a new packing technique. The packaging utilizes an electroless plated Ni/Pd/Au surface, resulting in a significant enhancement of the packaging hermeticity by orders of magnitude, approaching the level of <5 × 10-9 Pa·m3/s. Both Sn63Pb37 and Au80Sn20 solder alloys demonstrate exceptional solderability, attributed to Pd atoms diffusing to the Au layer during soldering at 310 °C. A reliability test of the packaging shows that the shear strength of the solder balls drops after thermal shocks but negligibly affects the hermeticity of the packaging. Furthermore, a meticulously designed internal vertical interconnect structure and I/O interconnections were engineered in the ball grid array packaging, showcasing excellent transmission characteristics within the 10-40 GHz frequency range while ensuring effective isolation between ports.

A new method for preventing stress cracking in repairable ceramic packages by changing the sealing ring shape

High-reliable ceramic packages are impressionable to the parallel seam welding (PSW) parameters leading to low yield and reliability. In this study, the structure of the ceramic package was modified by changing the sealing ring to improve weldability and high-temperature reliability. Three types of ceramic packages with different-shaped sealing rings, which are conventional rectangular rings, notch inward rings, and notch outward rings, were fabricated by Au-Sn soldering and a follow-up PSW process. The packages with the rectangular ring failed in the subsequent high-temperature aging test. The packages with the notch inward ring exhibited an early failure after PSW. Cracks were generated in the Au-Sn solder and propagated into the ceramic substrate. The packages with the notch outward ring exhibited remarkable weldability and reliability. Sequential thermo-structural coupling was used to simulate the temperature and stress distribution in the packages. The maximum principal stress in the aforementioned ceramic substrates rapidly increased to approximately 170.0 MPa, 168.5 MPa and 101.4 MPa in the PSW process. Stress concentration existed at the outside corner around the rectangular and notch inward-shaped sealing rings. The maximum temperature at the local position in the ceramic was raised to 250.3 °C, 238.6 °C and 157.2 °C depending on the shape of the sealing ring. The extra transmission path in the notch outward ring relieved thermal mismatch and deformation at the Au-Sn/ceramic interface during PSW. The packages with notch outward rings were recommended especially in the repairable ceramic packaging.

Oxidation thermodynamics and oxidation kinetics analysis of Au-20Sn solder

In this paper, the oxidation thermodynamics and oxidation kinetics of Au-20Sn solder at various temperatures were analyzed. The results indicated that the critical oxygen partial pressure to form SnO and SnO2 in Au-20Sn solder could be 1 × 10−44 Pascal (Pa) and 1 × 10−91 Pa at the temperature of 298 K, respectively. The oxidation kinetics analysis results indicated that the oxide on the surface of Au-20Sn solder consists mainly SnO2, while the major constituent of internal oxide is SnO. The reliability test results under salt spray environment have showed that the hermeticity of the package device gradually decreased with the increasing oxygen content in Au-20Sn solder. Meanwhile, the measured leakage rate of the packaging device could be lowered than 5 × 10−9 Pa·m–3·s–1 when the oxygen content in Au-20Sn solder is less than 28 ppm after high temperature aging.

DUV-LED packaging using high density TSV in silicon cavity and laser-glass-frit-bonded UV transmitting glass cap

This paper reports an improved deep ultraviolet LED (DUV-LED) packaging based on Si Micro-Electro-Mechanical Systems (MEMS) process technology. The Si package (Si-PKG) consists of a cavity formed by Si crystalline anisotropic wet etching and through-silicon vias (TSVs) filled with electroplated Cu. The Si-PKG is hermetically sealed by laser local heating of screen-printed glass frit. This technology allows for the use of a DUV-transparent glass substrate, which has an unmatched coefficient of thermal expansion (CTE). Using a high-density array of TSV capped with AuSn solder bumps, the cooling performance of the DUV-LED has been greatly improved. And the contribution by the Si (111) side reflection of Si-PKG to the total light output was confirmed 13 %. As a result, an optical output of 114 % (50 mW) and a volumetric light power density of 380 % (14 mW/mm3) were recorded compared with the conventional AlN-packaged device. The developed compact low-cost Si-PKG is promising for wider applications of the DUV-LED including the disinfection of the new coronaviruses.

Wetting behavior of eutectic Au–Sn solder on Ni/Au metallization at different temperatures

Wetting behavior of eutectic Au–Sn solder on Ni/Au metallization at different temperatures

Atomic-level study of AuSn–Au5Sn eutectic interfaces

Au-20Sn solder is obtained through severe plastic deformation and subsequent spheroidization of Au-20Sn eutectic alloys, which are composed of alternating intermetallic compounds δ-AuSn and ξ′-Au5Sn. Understanding AuSn–Au5Sn eutectic interfaces is essential for processing the Au-20Sn solder. Here, we studied the δ-AuSn/ξ′-Au5Sn eutectic interfaces at different deformation sates by electron backscattered diffraction analysis, high resolution transmission electron microscope, and first-principles density-function theory (DFT) calculations. We observed three orientation relationships and corresponding interfaces. One is thermally preferred during casting, and the other two are formed during the hot rolling process. Crystallographic analysis and DFT calculations suggest that the dominant orientation relationship is attributed to the small lattice mismatch and the low interface formation energy. These results provide insights for understanding the interface effect on microstructure evolution of ingot Au-20Sn alloys during severe plastic deformation.

Sintering of SiC chip via Au80Sn20 solder and its joint strength and thermomechanical reliability

The metallic packaging remains a big challenge for solid-state, high-power-density electronic devices, such as SiC chips, due to the frequent failure of solder joints in these components. Herein, the SiC Schottky diode was successfully soldered on a Mo substrate using eutectic Au80Sn20 solder at a low temperature of 320 °C. The results show excellent reliability and performance of the SiC chips. The chips can maintain outstanding performance after 2000 h at 280 °C and 500 cycles of heating and cooling experiments. Hence, this study demonstrates that this welding method has potential applications in high-power SiC chips with excellent thermomechanical reliability.

Tuning the microstructure and enhancing the mechanical properties of Au-20Sn/Au/Ni(P)/Kovar joint by ultrasonic-assisted soldering method

Improving the reliability of the solder joint has been the recent research focus in the electronic packaging field due to the increasing degree of integration in the electronic devices. During the reflow soldering process, when the local component is heterogeneous, the coarse structure of the solder joint is easy to grow, which deteriorates the performance of the solder joint. In this study, Au-20Sn/Au/Ni(P)/Kovar joints were prepared using ultrasonic-assisted reflow soldering process. Ultrasonication during reflow improved the wettability and shear strength between the Au-20Sn solder and Kovar substrate. The applied ultrasound can break the primary Au 5 Sn grain and refine the eutectic microstructure through acoustic cavitation. Meanwhile, ultrasound induced the formation of a new intermetallic compound (IMC) layer that was identified as Ni 3 P ( ca 120 nm), which inhibited the diffusion of Ni from substrate into the solder matrix. The mechanical properties of Au-20Sn/Au/Ni(P)/Kovar joint treated with 80 W ultrasonic vibration (USV) increased by 46.94% as compared to the control sample. The current study provides a new strategy for high-performance packaging in electronic devices in extreme environments.

Effects of Trace Oxygen Content on Microstructure and Performances of Au-20Sn/Cu Solder Joints

The Au-20Sn solder is widely used in the packaging of high-end electronic products, and the requirement on the reliability of the solder joints is more and more strict with a continuous increase in the performance of the package products. As the oxygen content in the Au-Sn solder is a key factor dominating the quality of fluxless packaging, in this study, the wettability and spreading performance of the Au-20Sn solder with different oxygen contents and the interfacial microstructure, mechanical properties, gas tightness and ratio of soldering area of the Au-Sn/Cu solder joints prepared using these solders were comprehensively investigated to clarify the effects of trace oxygen content. The results reveal that the wetting and spreading performances of the solder decrease sharply with increasing oxygen conte[nt. When the oxygen content increased from 18 to 77 ppm, the spreading area of the solder on the Cu substrate decreased from 92.8 to 49.2 mm2, reducing by 47%. Meanwhile, pores and microcracks appear in the solder joint with relatively high oxygen content, making the shear strength decrease from 56.6 to 31.7 MPa. The oxygen also greatly affects the gas tightness and ratio of soldering area. For the optical window packaged using Au-Sn solder containing 40 ppm of oxygen, the leakage rate was higher than 5 × 10−11 mbar·m−3·s−1 and cannot fulfill the requirements. With increasing oxygen content in the Au-Sn solder, the cleanliness of the chip packaged with these solders deteriorated, and the solder surface was obviously oxidized. When the oxygen content was 18 ppm, the ratio of soldering area was 92%, but decreased sharply to 53% when the oxygen content increased to 77 ppm. It is demonstrated that an oxygen content lower than 27 ppm is required for the Au-20Sn solder used in fluxless packaging.

Effect of microstructure of Au80Sn20 solder on the thermal resistance TO56 packaged GaN-based laser diodes

Au80Sn20 alloy is a widely used solder for laser diode packaging. In this paper, the thermal resistance of GaN-based blue laser diodes packaged in TO56 cans were measured by the forward voltage method. The microstructures of Au80Sn20 solder were then investigated to understand the reason for the difference in thermal resistance. It was found that the microstructure with a higher content of Au-rich phase in the center of the solder and a lower content of (Au,Ni)Sn phase at the interface of the solder/heat sink resulted in lower thermal resistance. This is attributed to the lower thermal resistance of Au-rich phase and higher thermal resistance of (Au,Ni)Sn phase.

Characteristic morphologies that cause failure of Au80Sn20/AlN substrate solder joint under combined temperature cycle and current switch cycle tests

With the requirement of lead-free soldering technology in electronic industry for manufacturing lead-free electronic devices, Au80Sn20 solder has been developed and applied in high-power devices due to its excellent physical and chemical properties. However, the application of new type of chip in high-power devices leads to the exposure of the Au80Sn20 solder joints to the complex environment of temperature cycle and current switch cycle, which seriously affects the reliability of solder joints in practical applications. In this study, the solder joint structure and simulation platform were designed independently. The failure mechanism of Au80Sn20/AlN substrate solder joint under temperature cycle and current switch cycle was studied by analyzing the changes in morphological characteristics of solder joint and composition in different working times. It was found that the failure process of solder joint involved the generation of steps along the grain boundary and phase boundary, and the failure was caused by the gradual expansion of steps. Owing to the uneven distribution of Cu and Ni in Au5Sn and AuSn phases, the volume difference among different phases was generated, which promoted the formation of phase boundary steps. The grain boundary steps were formed due to the formation of Au3Cu phase at the grain boundary, resulting in the volume difference between grain boundary and grain. Based on the research results, the idea of improving solder joint reliability by adjusting microstructure of Au80Sn20 solder is put forward, which plays a theoretical guiding role in the optimization of targeted performance of Au80Sn20 solder.

The impact of oxygen content on the reliability of Au-20Sn solder hermetic package

Hermetic sealing devices are produced with Au-20Sn solder at different oxygen content levels to study the reliability of the seal joints. Cross section of Au-20Sn solder joints processed with different oxygen content were examined by SEM, which shows that the microstructure displayed an obvious deterioration with the increase of oxygen content. It was found that bonding at 16 ppm oxygen content level, an uniform bonding interface with void-free was obtained with good hermeticity. However, when the oxygen content reached 55 ppm, voids and cracks were generated along the seal joint and the helium leak rate was higher than 5 × 10−8 atm cm3/s, which is the rejected limit value of MIL-STD-883 K. According to the reliability test results, we believe that the hermeticity deterioration is attributed to voids and cracks with the extension of aging time. In addition, samples with poor hermeticity were analyzed to know the failure mechanism of the seal joints and the feasible methods were proposed for improving hermeticity.

Formation of nano-phase Co3Fe7 intermetallic and its strengthening in Au80Sn20/CrMnFeCoNi solder interface

Abstract As one of the High entropy alloys, CrMnFeCoNi shows excellent mechanical properties. It is of great value to explore the joining behavior of CrMnFeCoNi in order to expand its application fields. In this paper, we have fabricated the Au80Sn20/CrMnFeCoNi solder joint using vacuum soldering. The results indicate that Au80Sn20 eutectic alloy wets CrMnFeCoNi high entropy alloy well. Vickers hardness of the intermetallic compounds (IMCs) is about 300HV, higher than Au80Sn20 solder; the shear strength of solder joint reaches 67.52 MPa, 1.5–2 times stronger than that soldering with Kovar alloy and pure nickel. The distribution of novel nanoscale Co3Fe7 particles in the IMCs layer significantly enhances the shear strength of solder joint. The results motivate a multi-elements strategy to enhance mechanical performance of joints, thus showing great potential in industrial application.

Interfacial evolution and mechanical properties of Au–Sn solder jointed Cu heat sink during high temperature storage test

The growth of interfacial intermetallic compounds (IMC) and mechanical properties by the widely used Au-Sn solder jointed Cu pillar are studied in this paper. Three concentrations of Sn (15%, 20%, and 25%) are employed to investigate the evolution of IMC growth and mechanical properties. It is found that the initial IMC growth is linear growth and surface reaction domination at the reflow step, as both Au and Sn directly react with Cu to form scallop-like (Au,Cu)Sn. Following the initial growth, IMC gradually becomes thicker, which inhibits Au/Sn penetrating into IMC to react with Cu, thus, at this stage, AuCu instead of (Au,Cu)Sn, forms the IMC and the inter-diffusion of parabolic growth dominates. By increasing HTS time, AuCu3 grows by consuming the AuCu compound. Moreover, the AuSn eutectic precipitations gradually decreased, which resulted in reduced hardness. Ductile fractures appeared among all the samples, and the appropriate IMC thickness improved the adhesion ability of the Au-Sn solder on the Cu pillar.

Influence of temperature on the soldering process of CLCC-3 package components using AuSn20 solder

In this study, a CLCC-3 shell and a cover were connected via soldering with AuSn20 as the solder. An Au–Sn eutectic reaction occurred during the sealing process. At high soldering temperatures, only the eutectic ζ′-Au5Sn and δ-AuSn phases remained. At the interface between the solder and the Au/Ni coating, Ni entered Au5Sn and AuSn to form (Au,Ni)5Sn and (Au,Ni)Sn and Au entered the lattice of the Ni3Sn2 phase to form the ternary compound (Ni,Au)3Sn2. The experimental results demonstrated that at a soldering heating plate temperature of 320 °C, the structure of the soldering area was compact and there were no holes in the soldering area. Under these conditions, the macroscopic appearance of the product improved, the solder was sufficiently melted, and the cover plate was well infiltrated, which resulted in the formation of a good, dense connection with the base plate.

Microstructural evolution and shear performance of AuSn20 solder joint under gamma-ray irradiation and thermal cycling

Owing to the excellent stability and mechanical strength, AuSn20 solder is of particular importance to the die attachment in aerospace power modules. An elevated requirement was put forward to improve the performance of solder joints for next-generation aerospace electronics. To this context, the microstructural evolution and mechanical performance of AuSn20 solder joints under independent γ-ray irradiation and thermal cycling were investigated in this work. The experimental results reveals that the shear forces of AuSn20 micro-joints were reduced by 17.5% and 25.3% after 1000 h of γ-ray irradiation and 200 thermal cycles, respectively, which are caused by the increase of interfacial IMC (intermetallic compound) layers and voids. Generally, the experimental data presented here are highly prospective because it provides new insights for the solder joint reliability in space environment, which could advance the research progress of aerospace devices without RHBD (radiation hardening by design) and ATCS (active thermal control system).

Microstructure Characterization and Interfacial Reactions between Au-Sn Solder and Different Back Metallization Systems of GaAs MMICs.

GaAs monolithic microwave integrated circuits (MMICs) with different back metallization systems (TiW/Au and Au/Ti/Au) exhibit different problems in the automatic Au-Sn eutectic bonding process, such as edge breakage or excessive voids. In this study, the formation mechanism of the edge breakage and excessive voids were investigated to prevent the damage of the MMICs in mass production scenarios. The microstructure and elemental distribution were studied using a scanning electron microscope and energy-dispersive spectroscopy. The void contents of the brazed region were measured with three-dimensional computed tomography. The top Au layer of the TiW/Au metallization partially dissolved in the melting An-Sn solder. Consequently, liquidus temperature of the solder increased, leading to isothermal solidification with the formation of ζ-Au5Sn in the scrubbing process, which was the reason for the edge breakage. The terminal Au film of the Au/Ti/Au metallization completely dissolved in the melting An-Sn solder. The metallurgical combination was achieved by the formation of the TiAu4 intermetallic compound between the Au-Sn solder and the Ti layer. The wettability of Au-Sn solder on Ti layer should be improved to prevent the formation of the excessive voids.