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Source publication
Purpose
Crack and stress distribution on dies are key issues for the pressure-assisted sintering bonding of power modules. The purpose of this research is to build a relationship among stress distributions, sintering sequences and sintering pressures during the sintering processes.
Design/methodology/approach
Three sintering sequences, S(a), S(b)...
Contexts in source publication
Context 1
... sintering process is conducted by a pressure sintering equipment as shown in Figure 2(a). Before the sintering process, the Ag film is laminated to the Ag-coated Mo layer at 130°C under 5 MPa for 2 min. ...
Context 2
... the sintering process, the Ag film is laminated to the Ag-coated Mo layer at 130°C under 5 MPa for 2 min. Figure 2(b) and (c) shows the morphology of the surface of the Mo layer before and after being laminated. The power chip used in this study is the dummy Si chip with Ag coated on the surfaces as shown in Figure 2(d). ...
Context 3
... 2(b) and (c) shows the morphology of the surface of the Mo layer before and after being laminated. The power chip used in this study is the dummy Si chip with Ag coated on the surfaces as shown in Figure 2(d). The sintering process is conducted at 250°C under 30 MPa for 3 min. ...
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Citations
... In recent times, some suppliers have developed pressure-assisted sintering equipment, and the sintering pressure and temperature range from 0.5-30 MPa and 220-270 ℃, respectively [33] . The selection of sintering pressure, which is an important factor for sintering efficiency, yield and cost management [34][35] , highly depends on the scale of the silver particle in the silver-sintering materials [36] . Tab. 2 lists the recommended pressure and cost estimation for the silver-sintering materials with scales of different particles [18,[32][33][37][38][39][40][41][42][43][44][45][46][47][48][49][50] . ...
... Pressure-assisted sintering could ensure the reliability of sintered silver attachment effectively. However, compared to bonding the discrete devices, the pressure-assisted sintering would lead to lower yield for fabricating high-density power modules integrated with multiple bare devices because it is difficult to obtain a uniformly distributed auxiliary pressure for each bare devices [34,56] . In addition, the pressure-assisted sintering requires a large investment in the sintering equipment and customized molds for different packaging cases. ...
... Therefore, those SiC modules with the pressure-less sintered nanosilver are believed to be approximately 40% better in heat-dissipating capacity than that of the traditional wire-bonding case. Considering that expensive SiC-based devices have higher Young's modulus than Si-based devices [15] , the pressure-assisted sintering is prone to damage the power devices, resulting in a low yield for multi-chip SiC power modules [34] . Therefore, using the pressure-less sintering for bonding SiC-based power chips with the small chip size is preferred for massive production. ...
Silver sintering is receiving increasing attention due to its novel die-attach technique for high-temperature power electronics. Excellent thermal conductivity, high melting point/remelting temperature and low-temperature sintering behaviors of the silver sintered attachment meet the requirements of high-temperature applications for power devices, specifically SiC devices. The merits and demerits of the existing pressure-assisted sintering and pressure-less sintering techniques using nano-scale, micro-scale and micro-nano-scale hybrid silver sintered materials are separately presented. The emerging rapid sintering approaches, such as the electric-assisted approach, are briefly introduced and the technical outlook is provided. In addition, the study highlights the importance of creating a brief resource guide on using the correct sintering methods.
... The microelectronic packaging industry has developed rapidly in the recent decades [1][2][3]. Due to reliability concern, the requirements for the Pb-free packaging materials are getting increasingly higher [4][5][6]. SnAgCu (SAC) alloys are the most widely used lead-free solders due to their comprehensive performances for industrialization [7][8][9]. ...
... The miniaturization of electronic devices causes the chips to face increasing heat density, which leads the solder joints to fail at high temperature. Improving the thermal property of solder joints plays an important role in enhancing the reliability of solder joints [3][4][5][6][7]. Eutectic Sn58Bi (SnBi) alloy with a melting point of 139 °C is widely used in low temperature packaging [8,9]. ...
This paper aims to examine the thermomechanical response of sintered silver die attachments in power electronics using finite element analysis (FEA). In this work, several material parameters of the sintered silver bonds are investigated. Additionally, two common solder creep constitutive laws including Anand and Garofalo models are also studied. To ensure the fidelity of the simulation procedures, the finite element (FE) models are first correlated with digital image correlation data. Afterward, the FE models are utilized to examine the influence of the material and creep models on the die attach stresses, strains, and plastic works. The expected fatigue and lifetime predictions of the sintered silver layer are thoroughly discussed, accordingly. The results proved that the die attach layer mechanical response is highly driven by the material parameters and creep modeling procedures considered throughout the simulations. Thus, the resulting fatigue life is evaluated. Finally, a general modeling guideline for simulating thermomechanical response of sintered silver die attachments in power electronics are provided in great detail.
Finite element analysis (FEA) is perhaps the most popular technique used for simulating the thermally induced failures of sintered silver die attachments in power electronics. The accuracy of the stress-strain relationships estimations of power electronics is highly influenced by the material mechanical properties and the creep constitutive models used throughout the simulations. Therefore, current paper aims to investigate several Anand-based material properties of the sintered silver bonds considering several mechanical creep constitutive models effect of thermal fatigue life of sintered silver bonds using extensive three-dimensional FEA thermomechanical simulations. In this investigation, the FEA models are first correlated with the displacement results of the digital image correlation experiments. Furthermore, the effect of the material parameters and creep models on the solder stresses, strains, and inelastic strain energy densities and hence on the lifetime predictions of the die attachment layer is discussed in detail. The results showed that the solder behavior is highly dependent on the material parameters as well as creep modeling. Finally, a detailed discussion on the effect of such discrepancies on the predictions and evaluations of sintered silver die attachments fatigue life is also presented.
With the rapid development of nano/micro technology for commercial electronics, the typical interconnection method could not satisfy the high power-density packaging requirement. The 2.5D/3D integrated packaging was seen as a promising technology for nano/micro systems. The gold (Au) bump was the frequently used bonding method for these systems because of its excellent thermal, electric, and mechanical performance. However, relatively little work has been performed to analyze its height uniformity. In this study, the simulation and experimental methods were used to analyze the Au bump height uniformity. Firstly, the electroplating process of Au bump under different flow field parameters was simulated by COMSOL software. The simulated results indicated that the Au+ concentration polarization was the significant reason that caused the non-uniform distribution of Au bump along the wafer radius. Meanwhile, the flow field parameters, such as inlet diameter, inlet flow, titanium (Ti), wire mesh height, and Ti wire mesh density, were optimized, and their values were 20 mm, 20 L/min, 12 mm, and 50%, respectively. Subsequently, the Au bump height uniformity under different current densities was analyzed through an experimental method based on these flow field parameters. The experimental results showed that the increases of current density would decrease the Au bump height uniformity. When the current density was 0.2 A/dm2, the average height, range, and deviance values of Au bump were 9.04 μm, 1.33 μm, and 0.43 μm, respectively, which could reach the requirement of high density and precision for 2.5D/3D integrated packaging.
Metal foam with excellent ductility was added into nano-Ag sintered joint to obtain the composite sintered joint with a sandwich structure of sintered Ag/metal foam/sintered Ag. The microstructure, shear behavior and fracture morphology of the composite sintered joint were investigated in this study. Experimental results indicate that the addition of ductile metal foam enhances the plasticity of composite sintered joint. As the number of pores of Cu foam increased from 110 to 500 per inch, the shear strength increased from 8.28 to 11.26 MPa. The composite sintered joint with 110ppi (pores per inch) Ni foam showed a higher shear strength than the other composite sintered joints did because of the higher Young’s modules and shear modules of Ni foam. In the Ni foam@nano-Ag composite sintered joint, cracks appeared at the interface between the metal foam and the nano-Ag sintered structure because of the mismatch of coefficient of thermal expansion (CTE). Compared with the Ni foam, the addition of Cu foam effectively depressed the generation of cracks at the interface between the metal foam and the nano-Ag sintered structure.
Cu foam (Cu-F) and Ag-coated Cu-F were added into nano-Ag paste to obtain Cu-F@nano-Ag composite sintered joint. The microstructure, hardness, and shear behavior of the sintered joints were investigated. Experimental results indicated that the addition of Cu-F and Ag-coated Cu-F suppressed the generation and propagation of cracks at the interface of the sintered joint. As the thickness of the Cu-F increased from 0.1mm to 0.2mm, the deformation ratio of the Cu-F sheet raised from 12 % to 50 %. Thereby, the hardness and bonding strength of the sintered joint was improved due to the microstructural densification. The bonding quality between Cu-F and sintered Ag is enhanced by the Ag-coating treatment. Therefore, the Ag-coated composite joints show higher shear strength than the others.
Copper foam (Cu-F) was added into nano-Ag paste to obtain nano-Ag@Cu-F composite sintered joint. The microstructure, hardness, and shear behavior of the joints were investigated in comparison with the nano-Ag sintered joints. Experimental results indicated that the addition of Cu foam significantly decreased the void percentage at the sintered interface. The average hardness of the nano-Ag joints sharply increased from 0.64 to 1.46 GPa as the sintering time extended from 5 to 15 min. In contrast, the nano-Ag@Cu-F sintered layers were condensed within 5 min and the hardness reached 1.41 GPa. Further extension of the sintering time led to slow increase of the hardness. The shear strength of the sintered joints was enhanced due to the addition of Cu foam. Compared with the nano-Ag sintered joints, the composite joints showed greater shear distance to failure during the shear test. The shear fracture occurred in the sintered layer instead of the interface in the nano-Ag@Cu-F sintered joints since the bonding interface was enhanced by Cu foam addition. As the sintering time prolonged, the bonding quality of the sintered joints was improved and led to the increasing of shear strength.
Purpose
The purpose of this paper was to investigate an influence of a low temperature pressureless sintering process of silver paste on the quality of sintered joints.
Design/methodology/approach
The authors analyzed various curing conditions of the paste during its sintering process: 175°C/90 min, 200°C/60 min, 250°C/30 min, 250°C/60 min, 350°C/30 min and 350°C/60 min. They analyzed an influence of the surface plating applied on a ceramic substrate/layer (Cu, Ag, AgPt and Au thick film) on the joints quality. The authors analyzed microstructure and electrical resistance of the joints. They evaluated these properties from the point of view of thermal aging process and changing resistance, after a constant current loading of the sintered joints.
Findings
The nanoscale pressureless silver paste can be applied for replacing a pressure-assisted micro-sized silver paste. It was found that the quality of the metal plating applied on the ceramic substrate/layer has a significant impact on the quality of the sintered joints. Copper and AgPt plating have better impact on quality of sintered joints in compare with Ag plating.
Originality/value
This investigation of the quality of the pressureless sintered joints at the silver-silver interface reveals an evident cracking immediately after the silver paste curing. Rapid sintering process typical for silver-based films on the substrate is because of the inter-diffusion between the micro and nanoparticles of silver at interfacial interface.
