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Ag sinter joining technology has gained increasing attention for its excellent thermal and mechanical properties, especially for high-temperature applications. This study focuses on the lifetime prediction of a SiC power module by Ag sinter joining based on mechanical properties including tensile, fatigue, and creep properties from room temperature to 200°C, as well as thermal properties including thermal conduction and the coefficient of thermal expansion. These mechanical properties and thermal properties of sintered Ag paste were evaluated in the study and the results show that mechanical properties of sintered Ag largely depend on the test temperature. The sintered Ag paste tends to soften at high temperature, and the fracture changed from nearly brittle to totally ductile with the testing temperature increase. From the S–N curve, the fatigue is close to the Morrow equation but not the Coffin–Manson law at room temperature. The finite element simulation of the lifetime based on Morrow’s equation for the sintered Ag layer shows that there has a crack occurrence with one fourth the side length after 10,000 cycles from − 40°C to 200°C but the crack extension area is less than one tenth of the sintered Ag layer. This study will add to the understanding of the high temperature properties and high temperature reliability as well as the lifetime of Ag sinter joining in high-temperature applications.

Ga and Ga-based alloys have received significant attention due to their potential application in the liquid state for low-temperature bonding in microelectronics. This study investigated the interfacial reactions between liquid Ga and pure Cu substrates at room temperature. The directional thermal expansion behaviour of the resulting CuGa2 was analysed by synchrotron x-ray powder diffraction with supporting observations of single crystal foils in high-voltage transmission electron microscopy. The mechanical properties of CuGa2 were evaluated by nano-indentation. CuGa2 was found to have advantages over other intermetallics that are present in assemblies made with current generation lead-free solders, including Ag3Sn, Cu6Sn5 and Cu3Sn. In addition to enabling lower process temperatures, solder alloys that form CuGa2 at the interface with Cu offer the possibility of providing more reliable connections in the very small joints that play an increasingly important role as the trend to miniaturisation of electronics continues.

Whiskering is a spontaneous filamentary growth of material, and it is a major long-term reliability issue affecting microelectronic packages comprising Sn plating and Sn-rich solders. In particular, whisker growth out of Sn-plated surfaces has been studied extensively in recent years due to the advent of next-generation, environment-friendly, Pb-free microelectronic packaging. Here, we review this scientifically challenging and technologically important problem, especially in the light of relatively new insights gained in the recent past, intending to provide a quick overview of the important results and stimulating future studies. In particular, we discuss the mechanisms of whisker growth by critically examining the roles of stress and its regeneration, oxide layer, diffusion conduits, and crystal anisotropy in creating conditions conducive for whiskering. We also discuss the recent proposals for effectively mitigating whisker growth in Sn coatings. Finally, an outlook is provided, with details of important unresolved issues related to whisker growth.

The coarsening of Ag 3 Sn particles occurs during the operation of joints and plays an important role in failure. Here, Ag 3 Sn coarsening is studied at 125°C in the eutectic regions of Sn-3Ag-0.5Cu/Cu solder joints by SEM-based time-lapse imaging. Using multi-step thresholding segmentation and image analysis, it is shown that coalescence of Ag 3 Sn particles is an important ripening process in addition to LSW-like Ostwald ripening. About 10% of the initial Ag 3 Sn particles coalesced during ageing, coalescence occurred uniformly across eutectic regions, and the scaled size distribution histograms contained large particles that can be best fit by the Takajo model of coalescence ripening. Similar macroscopic coarsening kinetics were measured between the surface and bulk Ag 3 Sn particles. Tracking of individual surface particles showed an interplay between the growth/shrinkage and coalescence of Ag 3 Sn.

Wafer-level solid liquid interdiffusion (SLID) bonding, also known as transient liquid-phase bonding, is becoming an increasingly attractive method for industrial usage since it can provide simultaneous formation of electrical interconnections and hermetic encapsulation for microelectromechanical systems. Additionally, SLID is utilized in die-attach bonding for electronic power components. In order to ensure the functionality and reliability of the devices, a fundamental understanding of the formation and evolution of interconnection microstructures, as well as global and local stresses, is of utmost importance. In this work a low-temperature Cu-In-Sn based SLID bonding process is presented. It was discovered that by introducing In to the traditional Cu-Sn metallurgy as an additional alloying element, it is possible to significantly decrease the bonding temperature. Decreasing the bonding temperature results in lower CTE induced global residual stresses. However, there are still several open issues to be studied regarding the effects of dissolved In on the physical properties of the Cu-Sn intermetallics. Additionally, partially metastable microstructures were observed in bonded samples that did not significantly evolve during thermal annealing. This indicates the Cu-In-Sn SLID bond microstructure is extremely stable.

This study attempts to join copper (Cu) and aluminium (Al) sheets in micro-thickness by using friction stir welding. These materials are being used as current collectors in lithium-ion (li-ion) battery which are employed as power sources for electric vehicles. Several experiments have been carried out, followed by the measurement of electrical conductivity by using a 4-probe setup and electrochemical analysis by using a potentiodynamic polarization test and an electro impedance spectroscopy test in lithium phosphorus hexafluoride (LiPF6), an electrolytic medium. The welded samples have been found to achieve an electrical conductivity of 9% less than the base Cu and the corrosion resistance of the welded samples has been found to be increasing because of the formation of inter-metallic compounds such as Al4Cu9, AlCu4 and AlCu at the weld interface. Among them AlCu4 has the highest hardness and the recovery elastic modulus than the rest.

Antimony is attracting interest as an addition to Pb-free solders to improve thermal cycling performance in harsher conditions. Here, we investigate microstructure evolution and failure in harsh accelerated thermal cycling (ATC) of a Sn-3.8Ag-0.9Cu solder with 5.5 wt.% antimony as the major addition in two ball grid array (BGA) packages. SbSn particles are shown to precipitate on both Cu 6 Sn 5 and as cuboids in β-Sn, with reproducible orientation relationships and a good lattice match. Similar to Sn-Ag-Cu solders, the microstructure and damage evolution were generally localised in the β-Sn near the component side where localised β-Sn misorientations and subgrains, accelerated SbSn and Ag 3 Sn particle coarsening, and β-Sn recrystallisation occurred. Cracks grew along the network of recrystallised grain boundaries to failure. The improved ATC performance is mostly attributed to SbSn solid-state precipitation within β-Sn dendrites, which supplements the Ag 3 Sn that formed in a eutectic reaction between β-Sn dendrites, providing populations of strengthening particles in both the dendritic and eutectic β-Sn.

Creep of directionally solidified Sn-3Ag-0.5Cu wt.% (SAC305) samples with near-  orientation along the loading direction and different microstructural lengthscale is investigated under constant load tensile testing and at a range of temperatures. The creep performance improves by refining the microstructure, i.e. the decrease in secondary dendrite arm spacing ( λ 2 ), eutectic intermetallic spacing ( λ e ) and intermetallic compound (IMC) size, indicating a longer creep lifetime, lower creep strain rate, change in activation energy ( Q ) and increase in ductility and homogeneity in macro- and micro-structural deformation of the samples. The dominating creep mechanism is obstacle-controlled dislocation creep at room temperature and transits to lattice-associated vacancy diffusion creep at elevated temperature ( T T M  > 0.7 to 0.75). The deformation mechanisms are investigated using electron backscatter diffraction and strain heterogeneity is identified between β -Sn in dendrites and β -Sn in eutectic regions containing Ag 3 Sn and Cu 6 Sn 5 particles. The size of the recrystallised grains is modulated by the dendritic and eutectic spacings; however, the recrystalised grains in the eutectic regions for coarse-scaled samples (largest λ 2 and λ e ) is only localised next to IMCs without growth in size.

(Bi0.25Te0.75)2Te3 (p-Bi2Te3) is thermoelectric material that can harvest waste heat into useful electric power. A severe reaction between p-Bi2Te3 and Sn-based solder decreases the reliability of thermoelectric modules. Sn/p-Bi2Te3 and Sn3.0Ag0.5Cu (SAC305)/p-Bi2Te3 with and without electroless Co-P at the interfaces were investigated in this study. Without a Co-P layer, brittle SnTe, Sn3Sb2, and Bi precipitates formed at the interface. A thin layer of SnTe after reflow results in growth of a layer-type Sn3Sb2 instead of a strip-like Sn3Sb2. The addition of a Co-P layer to both systems successfully inhibited the formation of brittle intermetallic compounds. Shear test results confirmed that the Co-P diffusion barrier also effectively increased the joint strength.

Low-temperature and pressureless silver (Ag) sintering was applied to a 1200 V/200 A silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (MOSFET) power module with a Ag-finished silicon nitride active metal-brazed substrate, and the results were evaluated for applicability in electric and hybrid electric vehicles. The sintering was performed at 220–240°C, 90 min in vacuum under nitrogen gas conditions; the bonding strength, bonding layer thickness (BLT), void content, and densification of the as-sintered Ag joints were 39 MPa, 71.4 µm, 2%, and 90.5%, respectively. The shear strength, BLT, densification, and microstructure of the Ag-sintered joints were compared before and after the thermal cycling test (− 50–150°C, 1100 cycles, TCT) and high temperature storage test (200°C, 1000 h, HTST). To simultaneously compare the electrical properties of the SiC power module with lead (Pb)-free solder joints, the same SiC MOSFET power module was manufactured using a Sn-3.0Ag-0.5Cu (SAC305) Pb-free solder. The shear strength and densification after TCT and HTST were 35.5 MPa and 39.7 MPa, as well as 92.8% and 94.8%, respectively. The on-resistance and total switching efficiency of the SiC power module with the Ag-sintered joint were also compared to those of the SAC305 solder joint module, which evinced maximum values of 7.3 mΩ and 10.7 mJ that were superior to those of 8.5 mΩ and 11.3 mJ for the SAC305 solder joint, respectively. Under the same measurement conditions, the maximum generated current and voltage values are lower than those of the solder joint module, so it is envisaged that stable power module operation is realizable for long-term use. The Ag-sintered joint surpassed the SAC305 solder interconnects in terms of the electrical and mechanical reliability of the power module. When a SiC wide band gap device was used, it was discovered that Ag sintering was superior to Pb-free solder interconnects to increase the power conversion efficiency of the power module.