Growth Of Interfacial IMCs Research Articles

Significant inhibition of interfacial Cu6Sn5 IMC and improvement of solder joint strength and reliability by applying (111) nanotwinned Cu substrate and vacuum soldering

In this research, (111) oriented nanotwinned Cu (nt-Cu) substrates, combined with vacuum soldering, were utilized to enhance the strength and reliability of the solder joints. The wettability of the composite solder Sn1.0Ag0.5Cu-Si3N4 (SAC105-Si3N4) was improved on the (111) nt-Cu substrates and the oxidization of the molten solder was avoided by the vacuum environment, ensuring the formation of regular and uniform solder joints. The (111) nt-Cu substrates, characterized by their low surface energy, are demonstrated to be highly efficient in restricting the growth of interfacial IMCs, and this effects becomes particularly pronounced in three-dimensional (3D) solder joints following extended high-temperature aging. In addition, with vacuum soldering, a continuous and uniform interfacial structure was obtained, which is essential for upgrading the reliability of 3D solder joints. Furthermore, the electron back scatter diffraction (EBSD) testing of the solder matrix and interface formed on the nt-Cu substrates revealed that the c-axis of the β-Sn grains was parallel to the (111) nt-Cu substrates, and that the c-axis of the Cu6Sn5 grains was approximated to be perpendicular to the (111) nt-Cu substrates in an air environment. Finally, the shear strength and fracture morphology of the solder joints were evaluated. The macroscopic voids inside the solder joints were suppressed under vacuum, and the solder joints formed on the (111) nt-Cu substrates provided the highest shear strength.

Effect of the ultrasonic-assisted soldering on the interfacial reaction and IMC growth behavior of SAC305 solder with Cu alloy substrates

Effect of the ultrasonic-assisted soldering on the interfacial reaction and IMC growth behavior of SAC305 solder with Cu alloy substrates

Interfacial IMC growth behavior and mechanical properties of Cu/Sn58Bi/Cu and Cu/Sn58Bi–0.05AlN/Cu solder joints under ultrasonic-assisted soldering

Interfacial IMC growth behavior and mechanical properties of Cu/Sn58Bi/Cu and Cu/Sn58Bi–0.05AlN/Cu solder joints under ultrasonic-assisted soldering

Microstructure evolution, IMC growth, and microhardness of Cu, Ni, Ag-microalloyed Sn-5Sb/Cu solder joints under isothermal aging.

In this work, various Cu, Ni, Ag-microalloyed Sn–5Sb/Cu joints, ordinary Sn–5Sb/Cu joints, and low-melting-point Sn–3Ag–0.5Cu (SAC305)/Cu (used for comparison) were prepared, focusing on the influence of Cu, Ni, and Ag on the microstructure evolution, interfacial IMC growth, and microhardness of Sn–5Sb/Cu joint under long-time isothermal aging process. Results showed that the microstructure of microalloyed joints consisted of β-Sn matrix, SbSn, and (Cu, Ni)6Sn5 and Ag3Sn compounds. (Cu, Ni)6Sn5 compounds generated a coarsening effect in the aging microalloyed joints, yet its coarsening speed is significantly lower than the ordinary Sn–5Sb/Cu. Meanwhile, the total IMC layer thickness increased with the rising aging time. A single fine dendritic (Cu, Ni)6Sn5 IMC at the interface of microalloyed joint was observed and evolved into a larger scallop or layer-like duplex IMCs ((Cu, Ni)6Sn5 + Cu3Sn) after the aging. Considering the combined effect of Cu, Ni, and Ag, the microalloyed joints exhibited the improved microstructure relative to ordinary counterparts and low-melting-point SAC305 materials, significantly inhibiting the interfacial IMC growth, especially Cu3Sn. The Cu3Sn IMC thickness and diffusion coefficient in the Sn–5Sb–0.5Cu–0.1Ni–0.5Ag/Cu joint were 0.71–2.81 μm and 0.96 × 10–6 μm·s−2, respectively. Besides, the precipitation strengthening mechanism triggered by the microalloyed elements was extremely obvious and the soldering and aging joints revealed superior microhardness values of 20–35 HV. This could effectively improve the application range of Sn–5Sb-based materials in higher-temperature package conditions such as third-generation semiconductors.

Effect of rapid thermal shock cycle on the thermomechanical reliability of 20Sn-80Pb solder bumps

The influence of rapid thermal shock(RTS) cycles on 20Sn-80Pb solder bumps was studied. In the study, 20Sn-80Pb solder bumps were prepared by desktop nitrogen lead-free reflow soldering machine. The prepared 20Sn-80Pb solder bumps were used for RTS test in the temperature rang of 0°C ~ 150°C. One cycle of RTS is 24 seconds, and the temperature rise and fall rate of RTS is 12.5 C/s. The result indicated that when the cycle of RTS reached 1500T (here T is cycle, the same below), the shear strength of Sn-80Pb solder bump dropped by drastically 48.6%. Whereas, when the cycle of RTS reached 5500T, 20Sn-80Pb solder bumps’ shear strength decreased to 18.35 MPa, which increased by 7.5% compared with that of l6.97 MPa at 4500T. With the increase of RTS cycles, 20Sn-80Pb solder bumps’ shear strength was a decreasing trend and the fracture mechanism changed from ductile fracture to ductile-brittle mixed fracture, which could be subject to the thickening of the interfaical IMCs and the stress concentration caused by the growth of interfacial IMCs. To understand the changes of the mechanical properties of 20Sn-80Pb solder bumps, the influences of RTS on the crack and interfacial IMC of 20Sn-80Pb solder bumps were studied in details.

Influence of ultrasounds on interfacial microstructures of Cu-Sn solder joints

PurposeThis study aims to investigate the interfacial microstructures of ultrasonic-assisted solder joints at different soldering times.Design/methodology/approachSolder joints with different microstructures are obtained by ultrasonic-assisted soldering. To analyze the effect of ultrasounds on Cu6Sn5 growth during the solid–liquid reaction stage, the interconnection heights of solder joints are increased from 30 to 50 μm.FindingsScallop-like Cu6Sn5 nucleate and grow along the Cu6Sn5/Cu3Sn interface under the traditional soldering process. By comparison, some Cu6Sn5 are formed at Cu6Sn5/Cu3Sn interface and some Cu6Sn5 are randomly distributed in Sn when ultrasonic-assisted soldering process is used. The reason for the formation of non-interfacial Cu6Sn5 has to do with the shock waves and micro-jets produced by ultrasonic treatment, which leads to separation of some Cu6Sn5 from the interfacial Cu6Sn5 to form non-interfacial Cu6Sn5. The local high pressure generated by the ultrasounds promotes the heterogeneous nucleation and growth of Cu6Sn5. Also, some branch-like Cu3Sn formed at Cu6Sn5/Cu3Sn interface render the interfacial Cu3Sn in ultrasonic-assisted solder joints present a different morphology from the wave-like or planar-like Cu3Sn in conventional soldering joints. Meanwhile, some non-interfacial Cu3Sn are present in non-interfacial Cu6Sn5 due to reaction of Cu atoms in liquid Sn with non-interfacial Cu6Sn5 to form non-interfacial Cu3Sn. Overall, full Cu3Sn solder joints are obtained at ultrasonic times of 60 s.Originality/valueThe obtained microstructure evolutions of ultrasonic-assisted solder joints in this paper are different from those reported in previous studies. Based on these differences, the effects of ultrasounds on the formation of non-interfacial IMCs and growth of interfacial IMCs are systematically analyzed by comparing with the traditional soldering process.

Influence of doping Ti particles on intermetallic compounds growth at Sn58Bi/Cu interface during solid–liquid diffusion

In this paper, 0.1 wt% Ti particles (2–5 μm) was incorporated into the Sn58Bi solder to improve the properties of Sn58Bi/Cu solder joint. The interface reaction and growth kinetics of the Sn–Cu IMC at the solder/Cu interface during solid–liquid diffusion at temperature of 180, 190 and 200 °C for three different time (10, 20 and 30 min) was systematically investigated. The solder/Cu interface presented a duplex structure of Cu6Sn5 and Cu3Sn IMC. The IMC thickness was developed with the higher soldering temperature and prolonged soldering duration. The diffusion coefficient (D) of different IMC layer increased with the increasing of soldering temperature. The activation energies (Q) of the overall IMC layer were calculated as 48.22 kJ/mol for Sn58Bi solder joint and 58.20 kJ/mol for Sn58Bi–0.1Ti solder joint. Especially, adding the 0.1 wt% Ti particles can inhibit the interfacial IMC growth during solid–liquid diffusion, which may be conducive to the improvement of the solder joint reliability.

Microstructures and properties of SnAgCu lead-free solders bearing CuZnAl particles

With the purpose of improving the properties of the Sn–3.8Ag–0.7Cu lead-free solder 0.5 wt% micro-CuZnAl particles were added. The experimental results showed that CuZnAl particles had little effect on the melting characteristics of Sn–3.8Ag–0.7Cu alloy. With the addition of CuZnAl particles, the tensile and shear stresses of solder joints were increased by 21% and 19%, respectively, and the microstructure matrix was refined obviously. However, the spreading area of solder was reduced by 7.2% and 3.6% at 230 °C and 250 °C on Cu substrates, respectively. In addition, the effect of CuZnAl particles on the growth of interfacial IMCs in the structure of Cu/Sn–3.8Ag–0.7Cu/Cu solder joints was studied. The results showed that the addition of 0.5 wt% CuZnAl particles could inhibit the growth of IMCs layer and the formation of voids.

Effect of in-situ formed Pr-coated Al2O3 nanoparticles on interfacial microstructure and shear behavior of Sn-0.3Ag-0.7Cu-0.06Pr/Cu solder joints during isothermal aging

Our previous research has already demonstrated the positive effect of in-situ formed Pr-coated Al2O3 NPs by developing a novel method of simultaneously doping 0.06 wt% surface-active rare-earth (RE) Pr and 0.06 wt% Al2O3 nanoparticles (NPs) into Sn-0.3Ag-0.7Cu solder. It not only addressed the issue of poor interface bonding between ceramic reinforcement (Al2O3 NPs) and solder, but also simplified the most-used modified technology of pre-decorating ceramic NPs with metals to enhance interface bonding. In this study, we focused on investigating the effect of in-situ formed Pr-coated Al2O3 NPs on the evolution of interfacial microstructures and resultant shear forces of the joints soldered with SAC0307-0.06Pr-0.06Al2O3 during solid state aging. The experimental results were compared with those of Sn-0.3Ag-0.7Cu-0.06Pr and Sn-0.3Ag-0.7Cu-0.12Al2O3. It was found the joint soldered with SAC0307-0.06Pr-0.06Al2O3 possessed a delayed growth of interfacial Cu6Sn5 IMCs and an enhanced shear force. This is attributed to a synergistic relationship established between Pr atoms and Al2O3 NPs, in the form of Pr-coated Al2O3 NPs, which effectively pinned the growth and development of interfacial IMCs during high temperature aging treatment. Theoretical analysis showed that the growth constants of total interfacial IMCs (DT) at the SAC0307-0.06Pr-0.06Al2O3/Cu interface was approximately 0.64 × 10−10 cm2/s, about 47.1% and 37.3% smaller than those at the interfaces of SAC0307-0.06Pr/Cu (1.21 × 10−10 cm2/s) and SAC0307-0.12Al2O3/Cu (1.02 × 10−10 cm2/s). Even after 840 h' aging treatment, the fractograph of the shear failure joint soldered with SAC0307-0.06Pr-0.06Al2O3 still exhibited a typical ductile fracture with smaller dimples than that soldered with SAC0307-0.06Pr.

Growth behavior of IMCs layer of the Sn–35Bi–1Ag on Cu, Ni–P/Cu and Ni–Co–P/Cu substrates during aging

In this work, the interfacial reactions and IMC growth of the Sn–35Bi–1Ag on Cu, Ni–P/Cu and Ni–Co–P/Cu were studied during reflowing at 220 °C for 10 min and solid–state treatment at 150 °C with various aging times. For the solder joints of Sn–35Bi–1Ag/Cu, Cu6Sn5 IMC was formed at the interfacial layer after soldering, while Cu3Sn appeared after aging treatment. In the case of the electroless Ni–P plating of Cu, the IMC formed at the interface during isothermal aging was mainly Ni3Sn4 and a small amount of P-rich Ni (Ni3P) layer between the Ni3Sn4 IMC and the electroless Ni–P plating layer. In the case of the electroless Ni–Co–P plating of Cu, the IMC formed at the interface during isothermal aging was mainly (Ni, Co)3Sn4 and a small amount of P-rich Ni ((Ni, Co)3P) layer between (Ni, Co)3Sn4 IMC and the electroless Ni–Co–P plating layer. The addition of Co atoms could effectively inhibit the IMC growth rate, which inducing a lower growth rate of (Ni, Co)3Sn4 than that of Ni3Sn4. The thickness of Ni3P and (Ni, Co)3P layer reached about 2.31 µm and 1.25 µm after aging for 360 h, respectively. Also, the growth kinetics of the Ni3P and (Ni, Co)3P layer was found to be a diffusion–controlled process, which followed a parabolic relationship in the thickness increase. During the aging, the consumption of the electroless Ni–Co–P plating layer was greatly reduced compared with that of the electroless Ni–P plating layer. Moreover, there were no voids observed in the electroless Ni–Co–P plating layer while some defects formed in that of the electroless Ni–P plating layer. The electroless Ni–Co–P plating layer will be a good diffusion barrier for the lead-free soldering.

Properties and microstructure of Sn–0.7Cu–0.05Ni lead-free solders with rare earth Nd addition

The effects of rare earth Nd on the melting behavior, wettability, microstructure and mechanical properties of Sn–0.7Cu–0.05Ni solders have been investigated in this paper. The melting temperature was found to be slightly influenced with rare earth Nd addition. Results of wetting balance tests showed that adding a proper amount of Nd could substantially improve the wettability of Sn–Cu–Ni solders by decreasing the wetting time and increasing the wetting force. The morphology evolution of solder matrix indicated that Nd contributed to the refinement and uniformity of the microstructure when added within an appropriate range. It was because the fine NdSn3 particles formed primarily in the soldering process would act as heterogeneous nucleation sites during solidification. However, excessive addition of Nd was inadvisable due to the formation of large amounts of brittle and hard NdSn3 compounds with bulk shapes. Meanwhile, moderate amount of rare earth Nd could inhibit the growth of interfacial (Cu,Ni)6Sn5 IMCs during soldering. Results of micro-joints strength test also discovered that Sn–Cu–Ni–Nd soldered joints possessed sounder shear strength, which resulted from the refined microstructure and the improved solders/Cu interfacial morphology. These above results evaluated that the optimum content of Nd added into Sn–0.7Cu–0.05Ni solders was about 0.06 wt%.

Effects of α-Al2O3 nanoparticles-doped on microstructure and properties of Sn–0.3Ag–0.7Cu low-Ag solder

In order to enhance the properties of Sn–0.3Ag–0.7Cu low-Ag solder, α-Al2O3 nanoparticles with various content (0–0.5 wt%) were successfully doped into the solder paste with a self-designed dispersion step. After comprehensive study of the microstructures and properties of the novel nano-composite solder, several satisfactory modified results can be obtained. For instance, the wettability of solder was greatly improved with trace amount of α-Al2O3 nanoparticles-doped. The superior wettability was achieved by Sn–0.3Ag–0.7Cu–0.12Al2O3 solder with spreading area approaching to ~ 79 mm2. Detailed thermodynamic and kinetic analysis of how α-Al2O3 nanoparticles promoting the processes of solder wetting and spreading on Cu substrate were given. In addition, the joint soldered with Sn–0.3Ag–0.7Cu–0.12Al2O3 displayed the highest shear force (57.1 N) with a typical ductile fracture failure mode. This relates to the evidently refined microstructure as well as the well-controlled growth of interfacial Cu6Sn5 IMCs. Corresponding theoretical analysis shows 0.12 wt% Al2O3 nanoparticles-doped can decrease the growth rate constant of interfacial Cu6Sn5 IMCs from 5.08 × 10−10 to 1.71 × 10−10 cm2/s.

Effect of indium addition on interfacial IMC growth and bending properties of eutectic Sn–0.7Cu solder joints

The microstructure and growth behaviors of interfacial IMCs between the Sn–0.7Cu–xIn (x = 0–5.0 wt%) solder and Cu substrate under solid aging were investigated. Bending test was conducted to evaluate the mechanical properties of Cu/Sn–0.7Cu–xIn/Cu solder joints. The needle-like Cu6(Sn,In)5 IMCs formed at interface instead of Cu6Sn5 in as-soldered In-containing solder joints. During solid aging, indium addition had little influence on the growth of Cu6Sn5 IMCs, but strongly suppressed the growth of Cu3Sn IMCs. In Sn–0.7Cu–5.0In/Cu couple, the maximum solubility of indium in Cu6Sn5 and Cu3Sn was about 4.9 and 3.1 at.% respectively which was independent of aging temperature. The average composition of Cu6(Sn,In)5 and Cu3(Sn,In) were given as Cu6(Sn0.89,In0.11)5 and Cu3(Sn0.88,In0.12). After indium addition, the diffusion coefficients were found to be lower than that of Sn–0.7Cu/Cu couple and the activation energy for the growth of Cu3Sn increased with the increase of indium content. Doping indium into Sn–0.7Cu solder improved the bending properties of solder joints. Interfacial cracks were suppressed effectively after long time aging with indium addition.

Effect of Pr addition on properties and Sn whisker growth of Sn–0.3Ag–0.7Cu low-Ag solder for electronic packaging

In this study, trace amount of rare earth Pr was added into Sn–0.3Ag–0.7Cu low-Ag solder to enhance properties of solders. Experimental results indicated that optimal amount of Pr addition (~0.06 wt%) can improve properties of wettability, shear force and ductility of Sn–0.3Ag–0.7Cu low-Ag solder. This is because that solder with optimal Pr addition not only had a refined microstructure but also owned a regular and thin interfacial IMC layer after soldering on Cu substrate. Meanwhile, we have explained the change of morphology and thickness of interfacial IMC layer after Pr addition based on Kim and Tu’s kinetic model of interfacial IMC growth. However, it was found excessive Pr addition led to the formation of PrSn3 phase, which was easy to be oxidized and became a great deterioration on the properties referred above. Besides, the fracture mode of solder joint also gradually changed from ductile fracture to cleavage fracture. Moreover, this oxidized PrSn3 became the birthplace of Sn whisker since it provided abundant supply of Sn sources and compressive stress for Sn whisker growth. By the in-situ observation of Sn whisker growth in 0.5 wt% Pr-doped solder joint, we obtained that the incubation period of Sn whisker is very short and its growth rate may have a great decrease with time extending. Besides, it was found after 1 day at room temperature, spindly and rod-like Sn whiskers also grew in 0.5 wt% Pr-doped solder joint besides dot-shaped Sn whisker that grew in 0.5 wt% Pr-doped solder matrix. We suggest this may be related with the extra compressive stress provided by interfacial IMC layer growth in 0.5 wt% Pr-doped solder joint.

Wettability and Shear Strength of Sn-Cu-Ni-xSi<sub>3</sub>N<sub>4</sub> Composite Solder

The wettability and mechanical properties of solder the joint of Sn-Cu-Ni-xSi3N4 had been investigated. In this study, five different silicon nitride (Si3N4) percentage addition were chosen (0 wt. %, 0.25 wt. %, 0.5 wt. %, 0.75 wt. %, and 1.0 wt. %). Contact angle measurement demonstrated that with Si3N4 addition, the wetting perfomances had been improved with the decrease of wettability contact angle. It is believed that the Si3N4 particles suppresses the interfacial IMC growth and thus improves the shear strength. Interfacial IMC thickness measurement and shear strength results showed that with thinner IMC layer (by increasing amount of wt.% of Si3N4), the higher the shear strength of the joint. Fracture surface of sheared samples shows a combination of both brittle and ductile fracture.

Effects of Ag content on the interfacial reactions between liquid Sn–Ag–Cu solders and Cu substrates during soldering

The effects of Ag content on the interfacial reactions between Sn–Ag–Cu (SAC) solders and Cu substrates during soldering were studied based on an experiment in which the liquid solder is removed after a long exposure time. This removal of the solder allows for the capture and visualization of the interfacial IMCs formed during soldering and avoids the influence of Cu6Sn5 precipitated from the solder matrix during cooling. The results showed that a Cu6Sn5 scallop type layer with round grains having a strong texture was formed at the interface of the SAC solders/Cu systems. The addition of Ag decreased the IMC/liquid SAC solder interfacial energy and improved the wettability of the solder on the Cu. In addition to the reaction energy, the interfacial microstructure also affected the interfacial IMC growth extent. By changing the growth environment near the interface, Ag affected the orientation of Cu6Sn5 grains formed at the interface, leading to the evolution of a microstructure that generates more Cu6Sn5 grain boundaries at the interface. Consequently, under the same reflow conditions, SAC solders with a higher Ag content in contact with the Cu substrate form thicker IMCs interfacial layers.

Influence of Activated Carbon Particles on Intermetallic Compound Growth Mechanism in Sn-Cu-Ni Composite Solder

The influence of Activated Carbon (AC) particles on mechanical properties of Sn-Cu-Ni-xAC solder joint was investigated. Five different Activated Carbon (AC) percentage addition (0 wt. %, 0.25 wt. %, 0.5 wt. %, 0.75 wt. %, and 1.0 wt. %) were prepared via powder metallurgy (PM) technique. Interfacial IMC thickness measurement and shear strength results showed that with thinner IMC layer (by increasing amount of wt.% of AC), the higher the shear strength of the joint. It is believed that the AC particles suppresses the interfacial IMC growth and thus improves the shear strength.

Interfacial reactions between electroplated Ni–Zn alloy films and lead-free solders

Because of the miniaturization trend in electronic devices in recent years, the issue of reliability of solder joints in these miniaturized devices becomes very critical. Studies have shown that a thin layer of Ni is effective in reducing the interfacial IMC growth between Cu and Sn-based solder. This is because the reaction kinetics of Ni–Sn compounds are much slower than that of Cu–Sn IMCs. In this study, zinc is incorporated into the nickel barrier film in the form of Ni–Zn alloy by electrodeposition. The effects of the presence of Zn on the interfacial reactions between nickel barrier film and Sn–3.8Ag–0.7Cu (SAC) and Sn–3.5Ag (SA) solders are investigated. Ni–Zn alloy films with 1.73 wt% Zn were prepared from ammoniacal diphosphate baths. Elemental composition of the alloy film was determined by energy dispersive X-ray spectroscopy while X-ray diffraction method was used to determine the phases present in the alloy film. Solders’ spreading rate was characterized with the use of optical microscope. Reflows were done for 1 and 12 cycles to investigate the effect of multiple reflows on the IMC growth and morphology. Results have shown that the IMC formed at the interface of SA/Ni and SAC/Ni was Ni3Sn4 and (Cu,Ni)5Sn6, respectively. (Ni,Cu)3Sn4 IMC was formed at the interface of SA/Ni–Zn alloy film. No spalling was detected at the SA/Ni–Zn solder joint. On the other hand, it has been observed that (Ni,Cu)3Sn4 and (Cu,Ni)6Sn5 layer with continuous non-uniform morphology were formed on the SAC/Ni–Zn alloy film after 1× reflow. As the number of reflow increased, (Cu,Ni)6Sn5 layer spalled from the interface leaving only (Ni,Cu)3Sn4 IMC at the interfacial region.

Influence of trace alloying elements on the ball impact test reliability of SnAgCu solder joints

In this work, we present ball impact test (BIT) responses and fracture modes obtained at an impact velocity of 0.8 m/s on SAC (Sn–Ag–Cu) package-level solder joints with a trace amount of Mn or RE (rare earth) additions, which were bonded with substrates of OSP Cu and electroplated Ni/Au surface finishes respectively. With respect to the as-mounted conditions, the Ni/Au joints possessed better impact fracture resistance than those with Cu substrate. Subsequent to aging at 150 °C for 800 h, multi-layered intermetallic compounds emerged at the interface of the Ni/Au joints and gave rise to degradation of the BIT properties. This can be prevented by RE doping, which is able to inhibit the growth of interfacial IMCs during aging. As for aged Cu joints, the Mn-doped samples showed the best performance in impact force and toughness. This was related to the hardened Sn matrix, and most importantly, a greater Cu 3Sn/Cu 6Sn 5 thickness ratio at the interface. Compared to Cu 6Sn 5, Cu 3Sn with a similar hardness but greater elastic modulus possessed better plastic ability, which was beneficial to the reliability of solder joints suffering high strain rate deformation if no excess Kirkendall voids formed.

Microstructure of eutectic 80Au/20Sn solder joint in laser diode package

Laser diodes (LD) are usually bonded onto heat sinks for the purposes of heat dissipation, mechanical support and electrical interconnect. In this study, energy dispersive X-ray analysis (EDX) and electron backscatter diffraction (EBSD) are employed to investigate the microstructure evolution of 80Au/20Sn solder joint in LD package. During reflow, Pt–Sn and (Au, Ni)Sn IMCs were formed at the respective LD/solder and solder/heatsink interfaces, while δ, β and ζ′ phases of Au/Sn intermetallics were found in the solder joint. The Au-rich β and ζ′ phases in the solder joint limit the growth of interfacial IMCs. Chip shear testing showed that the failure occurred within the LD, with partial brittle fracture at the GaAs substrate and partial interfacial delamination at the GaAs/SiN interface. The strong solder bond can be attributed to the high mechanical strength of 80Au/20Sn solder, which provides improved stability for high temperature applications.