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Owing to its cost-effectiveness and low coefficient of thermal expansion (CTE), micron Si is incorporated into sintered Ag matrix to develop an Ag@Si composite sintering strategy. The Si integration helps reduce cost and alleviate CTE-mismatch of Ag-sintered die attachments. An innovative Ag@Si composite sintering structure is achieved by low-temperature and pressure-less sintering process, where a possibly slight diffusion of native SiO 2 on the Si surface toward Ag is indicated by TEM observation, enabling the integration of Ag and Si into one continuous network. Owing to the robust well-bonded composite sintering, the Ag@Si joining strategy provides mechanical/microstructural reliability far beyond the pure Ag sinter joining, demonstrating significant prospects in high-temperature interconnection applications. During the harsh thermal cycling (−50–250 °C), the mitigating effect of the Si addition on CTE mismatch is manifested through the substantial suppression of microstructure deterioration in Ag@Si joint that occurs in pure-Ag-sintered joint, while the shear strength retention rate is doubled. Detailed investigation into the mechanism for elevated performance was conducted by material property and Missies stress analysis. The incorporation of Si helps modify the CTE, elastic properties, and stress distribution of Ag@Si-sintered material, synergistically contributing to the satisfactory joining reliability. [Display omitted] • The Ag@Si composite sinter joining was developed for power modules, where Si addition not only contributed to cost reduction but also helped alleviate CTE-mismatch issues in modules. • The Ag@Si sintering was revealed to be a well-integrated network between Ag and Si due to the slight diffusion of native SiO 2 on Si, offering good mechanical stability for the composite joining layer. • The integrated matrix endows Ag@Si sinter joint with much superior reliability to pure Ag sintered joining, both in terms of mechanical and microstructural stability during thermal cycling. • The impact of Si addition on alleviating CTE-mismatch was systematically validated through analyses of thermal expansion, tensile properties, and finite element method (FEM) simulation. [ABSTRACT FROM AUTHOR]

Silver (Ag) sinter-joining is an ideal connection technique for wide bandgap (WBG) power electronics packaging due to its excellent high-temperature stability and excellent thermal conductivity. In this work, we applied Ag sinter-joining to die attach for a WBG power module and focused reliability of Ag sinter-joining under harsh thermal and power cycling conditions. The die attach structure using a Ag flake paste had an initial shear strength of over 45 MPa due to the excellent sinter-joining ability of the paste. Variation of die attach shear strength and failure mode under a harsh cycling condition (−50~250 °C) have also been systematically discussed. Thermal diffusivity of sintered Ag and thermal resistance of the die attach structure were also measured, showing a superior thermal performance to solder materials. Meanwhile, a simple SiC diode module was assembled via Ag sinter-joining and aluminum (Al) ribbon-bonding for evaluation of Ag sinter-joining reliability during a severe power cycling condition. A power cycling test with a high junction temperature of 200 °C was conducted to evaluate the reliability of Ag sinter-joining. It is found that the main failure of the SiC diode module was located at ribbon-bonding rather than the Ag sinter-joining layer degradation, based on the variation of forward voltage and junction to case thermal resistance. This investigation indicates that the Ag sinter-joining has a long lifetime under a severe operating condition of power electronics. [ABSTRACT FROM AUTHOR]

An Ag–Au joint developed by Ag paste joining on electroless nickel/electroless palladium/immersion gold (ENEPIG)-plated direct-bonded aluminum (DBA) substrate was employed in SiC (Silicon carbide) power modules. The ENEPIG plating was modified to possess high mechanical strength by thickening the Ni layer to 20 μm. The reliability of SiC/DBA die-attached module by Ag–Au joining was evaluated during a long-term thermal shock test (TST) from − 50 to 250 °C up to 2000 cycles. The shear strength of as-sintered Ag–Au joint was evaluated to be 37.6 MPa, but it showed a significant decrease after 1000 thermal cycles and maintained stably from 1000 cycles to 2000 cycles. Based on the microstructural evolution via EBSD observation, it was confirmed, by modifying ENEPIG, the Ag–Au interfacial deformation derived from Al plastic deformation was successfully suppressed even after 2000 cycles. In this case, the mechanism for shear strength degradation was found to be the interfacial delamination between Ag paste layer and ENEPIG substrate. This can be ascribed to the large thermal stress caused by different coefficients of thermal expansion (CTE) of power module components. This study not only realized the deformation-free structure for Ag–Au joint during long-term thermal cycling but also provided fundamental insights for fracture behaviors of Ag–Au sinter joint. [ABSTRACT FROM AUTHOR]

Ag particle paste sintering has been developed and shown a good performance in areas such as high temperature reliability and high electronic conductivity. Recently, it was found that the microstructure of a sintered Ag layer exhibits a coarse-dense inhomogeneous distribution after sintering, which depends on the loading speed of a die during the chip mounting process due to the flow characteristics of the Ag particle paste. In this work, the effect of the die mounting speed and the push-in amount (push depth) in the die mounting process on the microstructure of the sintered Ag layer, shear strength and thermal cycling reliability of Ag sinter joint structures were investigated. The results show that the shear strength of the sintered Ag joints was largely influenced by the speed and push depth during mounting process. The fast push speed exhibited a better shear strength, and the push depth can be optimized to obtain a better shear strength. In addition, the reliability during the thermal cycling of the Ag sinter joint structures with different the die mounting speed and the push depth were evaluated during a thermal cycling test from − 40 to 175 °C for 500 h. Cracks propagated after the thermal cycle test at the high porosity area near the die edge when the die was mounted with a slow speed, leading to a shear strength quickly decreasing after the thermal cycle test. The die attached structure showed better thermal cycling reliability in the case where the die was mounted with a fast speed. [ABSTRACT FROM AUTHOR]

This study was carried out to develop a DBA (direct bonded aluminum) substrate with Ni/Ti/Ag metallization to achieve highly functional thermal shock stability of Ag sinter joining in GaN (Gallium Nitride) power modules. GaN /DBA die-attached module structures by Ag sinter joining was performed during harsh thermal shock cycling tests within a temperature range of − 50/250 °C. In the case of DBA without a Ni metallization layer (Ti/Ag), severe degradation occurred at the interface between the sintered Ag and Al due to significant plastic deformation of the Al layer. The shear strength decreased from an initial value of 33.1 MPa to 22.3 MPa after 500 cycles. With EBSD investigation, it was determined that the Al layer underwent sub-grain rotation recrystallization during thermal shock cycles. This led to a non-uniform grain orientation distribution at center and corner locations. On the other hand, Ni/Ti/Ag metallization showed that it can prevent severe Al deformation due to the superior rigidity achieved by Ni metallization. The die-shear strength maintained almost the same value as its initial value, even after 500 cycles. In addition, a numerical simulation analysis determined that the Ag sinter joining structure on the DBA substrate with Ni/Ti/Ag metallization had high functionality in stress relaxation. This study provided a novel approach to design thermal shock stability Ag sinter joining for next-generation power modules in high-temperature applications. [ABSTRACT FROM AUTHOR]

We studied the thermal fatigue behavior of submicron silicon carbide particle (SiC)-doped silver (Ag) microflake sinter joints for die attachment in next-generation power devices. Si dummy chips and direct bonded copper substrates with various metallization schemes were bonded using SiC-doped Ag microflakes under mild conditions (250°C, 30 min, 0.4 MPa). The SiC was distributed homogeneously in the porous Ag network and inhibited morphological evolution during thermal cycling tests. The shear strength of as-sintered pure Ag and SiC-added joints was ∼50 MPa and 35 MPa, respectively. Thermal cycling tests from −40°C to 250°C were conducted for up to 1000 cycles (hours) to characterize the thermostability of the bonded joints. After 1000 cycles, joints with and without SiC experienced bonding degradation, with shear strength of ∼25 MPa and 20 MPa, respectively. Thus, after 1000 cycles, the shear strength of pure Ag and SiC-doped joints decreased by 58% and 42%, respectively, compared with their maximum value. Coarsening of porous Ag occurred in pure Ag joints. SiC addition inhibited morphological evolution of SiC-doped joints during thermal cycling. However, vertical cracks generated by thermal stress were observed in joints both with and without SiC, which may limit long-term reliability. [ABSTRACT FROM AUTHOR]

The fracture behaviors and Ag–Au joint interface evolution of sintered micron-sized Ag particles paste joined on an electroless nickel/electroless palladium/immersion gold (ENEPIG)-plated direct-bonded aluminum (DBA) and direct-bonded copper (DBC) substrates are evaluated during an extreme thermal shock test (TST) from −50–250 °C. The die shear strength of the as-sintered Ag joint on the DBA substrate is evaluated to be 33.5 MPa at a sintering temperature of 200 °C without any assisted pressure, which decreased gradually with an increase in the thermal cycling number. The shear strength declined slightly but remained at approximately 20 MPa; subsequently, it decreased considerably to 11.2 MPa after 1000 cycles. Coarsening of the sintered Ag layer is observed as the microstructure inhomogeneity and vertical cracks increased after 1000 cycles. In addition, the Al layer induced a greater undulate deformation, resulting in a sintered Ag layer exhibiting partial compression and tension after a TST. The sintered Ag layer became dense with a significant decrease in porosity at the compression parts and large horizontal cracks appeared at the tension parts. Both of horizontal cracks and vertical cracks led to fracture mode change and shear strength decrease. The Ag–Au joint interdiffusion layer became thicker during thermal shock with the gradual diffusion of the Au atoms into the sintered Ag layer. The die shear strength of the as-sintered Ag joint on the DBC substrates is evaluated as 34.4 MPa at 200 °C sintering but decreased to 0 MPa after 250 thermal shock cycles owing to the stress-induced delamination between the Ag and Au interdiffusion layer and sintered Ag layer. This study provides insights into the interface reaction and evolution of sintered Ag on ENEPIG-finished DBA and DBC substrates for applications at high temperatures. ga1 • Ag-Au joint with 33.5 MPa shear strength was achieved by micron-sized Ag particle at 200 ℃ pressure-less. • Ag particle with nano-grains may play an important role in low temperature pressure-free sintering. • Ag-Au joint on DBA substrate exhibit a good thermal shock stability by relax stress on Al deformation. • Interface delamination occurred for Ag-Au joint on DBC substrate after 250 thermal shock cycling. [ABSTRACT FROM AUTHOR]

The thermal cycling life of direct bonded aluminum (DBA) and active metal brazing (AMB) substrates with two types of plating—Ni electroplating and Ni–P electroless plating—was evaluated by thermal shock tests between −50 and 250 °C. AMB substrates with Al2O3 and AlN fractured only after 10 cycles, but with Si3N4 ceramic, they retained good thermal stability even beyond 1000 cycles, regardless of the metallization type. The Ni layer on the surviving AMB substrates with Si3N4 was not damaged, while a crack occurred in the Ni–P layer. For DBA substrates, fracture did not occur up to 1000 cycles for all kind of ceramics. On the other hand, the Ni–P layer was roughened and cracked according to the severe deformation of the aluminum layer, while the Ni layer was not damaged after thermal shock tests. In addition, the deformation mechanism of an Al plate on a ceramic substrate was investigated both by microstructural observation and finite element method (FEM) simulation, which confirmed that grain boundary sliding was a key factor in the severe deformation of the Al layer that resulted in the cracking of the Ni–P layer. The fracture suppression in the Ni layer on DBA/AMB substrates can be attributed to its ductility and higher strength compared with those of Ni–P plating. [ABSTRACT FROM AUTHOR]

Negative thermal expansion not only challenges the traditional lattice concept, but also provides new opportunities for regulating the thermal expansion coefficient and addressing the increasing reliability demands in power device packaging. In this study, ZrW 2 O 8 nanorods were firstly introduced into the micron Ag paste via a facile low-temperature (≤ 300 ℃) low-pressure (< 10 MPa) sintering. The pinning and negative thermal expansion mechanisms contributed by the homogeneously dispersed ZrW 2 O 8 nanorods significantly mitigate the thermal expansion mismatch and suppress the microstructure deterioration in SiC power module, which was also verified by finite element (FE) simulation. The Ag@2%ZrW 2 O 8 (2% of the total weight of Ag) specimen possessed outstanding long-term reliability with a die-shear strength of 29.63 MPa after 1000 thermal shock cycles from −50–250 ℃. The novel findings can be inspiring on interconnected material optimization and selection in electric packaging application as well as reliability evaluation in the service condition. [Display omitted] • Ag/ZrW 2 O 8 pastes were synthesized and can be sintered in low-temperature low-pressure. • The CTE of sintered Ag paste was adjusted by addition of ZrW 2 O 8 nanorods. • The deterioration of joint structure during thermal shock test was suppressed by Ag/ZrW 2 O 8 paste. [ABSTRACT FROM AUTHOR]

Micro-via plays an important role in high density interconnect printed circuit boards, which provides electrical conduction among different ICs. Recently, it has been found that the micro-vias suffer reliability problems like cracking and delamination due to the poor quality of the electroless Cu layer. In this work, we compared two different electroless Cu depositions, a traditional electroless Cu deposition method that uses Ni as a stress-regulating additive and a newly developed "OPC-FLET" Cu deposition method without Ni additive. These two Cu depositions were comprehensively investigated by using SEM and TEM characterizations. It is found that the traditional electroless Cu method can induce nanovoids in the deposition layer, whereas the OPC-FLET method can create a nanovoid-free electroless Cu layer. The OPC-FLET method is regarded as a more reliable method for micro-via preparation due to its flawless structure. According to the EDS analysis results, the incorporation of Ni can be regarded as the main culprit for the nanovoids, which can speed up the electroless Cu reaction and thus induce abundant hydrogen bubbles. Meanwhile, 5 times reflowing processes (220 °C, 5 min) were implemented to observe the effects of nanovoids on the micro-via structure and a thermal cycling test ranging from −55 °C to 150 °C was also conducted to investigate the reliability of these two micro-via structures. • Micro-via structures with traditional and OPC-FLET electroless Cu layers were investigated. • Thermal reliability of micro-vias was also studied by reflowing and thermal cycling tests. • Ni effect on the electroless Cu deposition was elucidated. [ABSTRACT FROM AUTHOR]