Nanosilver Paste Research Articles

Flexible transparent electromagnetic interference shielding films with silver mesh fabricated using electric-field-driven microscale 3D printing

In order to address the challenging issue regarding the high-efficiency and low-cost fabrication of high-performance flexible transparent electromagnetic interference (EMI) shielding films, a novel approach is proposed to produce flexible transparent EMI shielding film with silver mesh based on electric-field-driven (EFD) microscale 3D printing. The manufacturing principle and the reasonable process parameters are revealed with a series of experiments. Following this fabricating scheme and self-developed EFD micro-scale 3D printer, three flexible transparent EMI shielding films having a size of 60 mm × 60 mm and a line width of 26 μm are achieved utilizing the low-temperature nano silver paste (75% silver content and 350 dPa·s (25 °C) dynamic viscosity). The experimental result shows that the adhesive force between the sintered silver mesh and the polyethylene terephthalate (PET) substrate is measured to be 5B with 3 M scotch tape. The bending experiment proves the excellent mechanical flexibility of the flexible transparent EMI shielding film. In different chemical environments and ultrasonic vibration environments, the silver mesh flexible transparent EMI shielding film can still maintain good electrical properties. When the pitch of the silver mesh is 500 μm, the optical transmittance is 90.5% and the EMI shielding efficiency for the common medium-high frequency electromagnetic wave is greater than 26 dB. When the pitch is 300 μm, the optical transmittance is 84% and the shielding efficiency is higher than 32 dB. When the pitch is 150 μm, the optical transmittance is 69% and the shielding efficiency is higher than 34 dB. As a result, the proposed method provides a promising solution for mass producing high-performance silver mesh flexible transparent EMI shielding films at low cost and high throughput.

Low-pressure micro-silver sintering with the addition of indium for high-temperature power chips attachment

Sintered silver paste is a popular material for die attachment technology in power electronics. However, using traditional nano-silver paste when fabricating sintered joints has intrinsic material problems that cannot be overcome, such as the high cost of nano-silver particles and their potential health hazards. In this study, a novel micro-silver paste was utilized for sintering and bonding to overcome the limitations of nano-silver paste. Although the micro-silver paste is an excellent candidate to replace nano-silver paste for sintering processes to reduce the potential harm to humans, the oxidation at copper substrates on both sides of the pure silver joint at 300 °C causes mechanical reliability issues in long-term high temperature applications. Therefore, a micro-silver paste was sintered with the addition of indium to address the Cu oxidation problem in this study. It was found that Ag–In intermetallic compounds (IMCs) formed through a transient liquid phase reaction. The results demonstrated that sintered joints comprising Ag–In IMCs and Ag–In solid solution phases could effectively resolve the oxidation issues and significantly enhance the high-temperature reliability. Furthermore, the Ag–In IMCs exhibited excellent mechanical properties, withstanding the thermal stress induced during the thermal cycling test.

Low Sintering Temperature Nano-Silver Pastes with High Bonding Strength by Adding Silver 2-Ethylhexanoate.

A silver precursor (silver 2-ethylhexanoate) and silver nanoparticles were synthesized and used to prepare a low sintering temperature nano-silver paste (PM03). We optimized the amount of silver 2-ethylhexanoate added and the sintering temperature to obtain the best performance of the nano-silver paste. The relationship between the microstructures and properties of the paste was studied. The addition of silver 2-ethylhexanoate resulted in less porosity, leading to lower resistivity and higher shear strength. Thermal compression of the paste PM03 at 250 °C with 10 MPa pressure for 30 min was found to be the proper condition for copper-to-copper bonding. The resistivity was (3.50 ± 0.02) × 10−7 Ω∙m, and the shear strength was 57.48 MPa.

Development of ecoflex based nano silver paste through photonic sintering process

Development of ecoflex based nano silver paste through photonic sintering process

Preparation and sintering characteristics of nanosilver-tin core–shell paste

Nanosilver paste, an interconnect solder, is a common choice in the electronic packaging industry; however, higher sintering temperatures and lower sintering strength limit its application. At present, core–shell nanoslurry has been studied and applied to chip interconnection. Based on the mechanism of heterogeneous flocculation, we have developed a new nanosilver wrapped tin paste (Sn@Ag paste), and according to the decomposition temperature of the organic dispersant in the slurry, a corresponding sintering process with a temperature of 300 °C was developed. The Sn@Ag core–shell structure makes Sn have good dispersibility and oxidation resistance, and the sintered product of the slurry is a mixture of a solid solution of Ag and an Ag3Sn phase. Among them, the hard and brittle phase Ag3Sn acts as a dispersion strengthening effect in the Ag matrix phase, and the solid solution of Ag acts as a replacement solid solution strengthening. With the increase of doping Sn content, the sintering strength is significantly improved. When the Sn content is 5%, the joint shear strength reaches the highest value of 55 Mpa, which is higher than the pure nanosilver paste by 10 Mpa. This new nanosilver wrapped tin paste technology has the characteristics of low-temperature sintering and high-temperature service.

Thermo-elasto-plastic phase-field modelling of mechanical behaviours of sintered nano-silver with randomly distributed micro-pores

Nano-silver paste is an emerging lead-free bonding material in power electronics, and has excellent mechanical properties, thermal conductivity and long-term reliability. However, it is extremely challenging to model the mechanical and failure behaviours of sintered nano-silver paste due to its random micro-porous structures and the coupled thermomechanical loading conditions. In this study, a novel computational framework was proposed to generate the random micro-porous structures and simulate their effects on mechanical properties and fracture behaviour based on the one-cut gaussian random field model and the thermo-elasto-plastic phase-field model. The elastic modulus, ultimate tensile strength and strain to failure are computed statistically, showing good agreement with the experimental results. Further, the framework was applied to model the fracture of sintered nano-silver paste under thermal cyclic conditions, demonstrating the formation of distinctive crack patterns and complex crack networks. The cracking behaviours observed in the experiments and simulations are remarkably similar to each other. The framework was implemented within Abaqus via a combination of subroutines and Python scripts, automating the process of model generation and subsequent computation. This study provides an efficient and reliable approach to simulate the mechanical and failure behaviours of sintered nano-silver paste with random micro-porous structures.

Size effect on the fracture of sintered porous nano-silver joints: Experiments and Weibull analysis

Nano-silver paste is a promising alternative of high temperature solder material for the next generation electronic devices, which is composed of organic solvent and silver nanoparticles/sheets. The mechanical properties of nano-silver interconnections are essential for the bonding between chip and substrate by sintering. During sintering process, volatilization and combustion of organic solvent in nano-silver paste lead to development of abundant voids in the joint, forming a three-dimensional network structure, which has strong influence on the mechanical properties. Sintering temperature and cross section area can affect the distribution of voids in solder joint. In the current study, effects of sintering temperature (200 °C, 250 °C, 300 °C) on the tensile and shear failure strength of sintered nano-silver joints were investigated, the size effect caused by different cross section area (i.e. (0.5, 1, 2, 3) × 5 mm2) was studied. The volatilization of organic solvent in nano-silver paste is the main reason for the porosity diversity, and the difference of porosity is one of the key factors causing size effect. It also leads to dispersion of experimental data of failure strength, thus, statistical analysis was performed to the experimental data. Four universal estimators and Weibull distributions were adopted to analyze the tensile and shear failure strength of sintered nano-silver joints. Based on the Gurson-Tvergaard-Needleman model, the critical porosity equation of fracture was developed. Furthermore, the relationship between critical porosity and size effect was established considering porosity increases with the increasing of cross section area, and a modified Weibull model containing size effect was proposed, which showed good agreement compared with the experimental data.

Evaluation of Thermal Contact Resistance in Nano-Silver Paste under High Heat Flux

Evaluation of Thermal Contact Resistance in Nano-Silver Paste under High Heat Flux

A Way to Reduce Leakage Current and Improve Reliability of Wire-Bonds for 300-A Multichip SiC Hybrid Modules

In this article, pressureless sintering of nanosilver paste is proposed to enhance the reliability of wire-bonds with SiC chips by both alleviating thermomechanical stresses and enhancing thermal coupling of bonding wires and chips. A multichip 1200-V/300-A SiC hybrid module with six Si IGBTs and 12 SiC Schottky barrier diodes (SBDs) is demonstrated. The lifetime of the wire-bonds with the SiC SBD bonded by the pressureless sintered nanosilver is ~27.9% longer than that by the high-temperature solder under power cycling with constant temperature swing. The lifetime of the wire-bonds with the IGBT also bonded by the pressureless sintered nanosilver is ~46.2% longer than that by the high-temperature solder under power cycling with constant conduction current. Furthermore, not only the cost of 1700-V SiC SBDs is quite similar to that of 1200-V ones but also the leakage current of the 1200-V/300-A SiC hybrid module can be reduced greatly using 1700-V SiC SBDs as free-wheeling diodes instead of the regular 1200-V ones. Considering the much larger leakage current of a SiC SBD compared with that of a Si p-i-n diode. It is feasible to use a SiC SBD with higher blocking voltage to reduce the significant leakage current of the free-wheeling SBD with almost no cost increase.

Mechanical and Microstructural Analysis of an Ultra-Flexible Nano-Silver Paste Sintered Joint

Soldering using common lead-free solder alloys is still one of the main die attach technology, in particular for applications in power electronics where high temperatures have to be met. However, some newly developed attach technologies promise to offer more interesting features in terms of both mechanical and thermal properties. Among these new methods, sintering of nano-silver particles allows to obtain a high thermal conductivity needed in the assemblies of electronic or optical components, as well as a relatively low elastic modulus for better stress accommodation and enhanced thermo-mechanical reliability. The sintering processing parameters, mainly the bonding pressure, the sintering temperature profile, and the sintering atmosphere, are known to have a critical effect on the properties of the sintered layer, such as its mechanical strength and electrical/thermal performances.In this study, copper substrates are fabricated and assembled by sintering using a nano-silver paste. The objective is to obtain a bonding joint with high mechanical flexbility, capable of addressing the thermomechanical stresses for systems operating under high temperatures. The measured mechanical properties of the sintered material show on the one hand low elastic modulus of the joint which is appropriate for strong difference in thermal expansion between components, and on the other hand sufficient mechanical strength for the assembly. Microstructure analyses reveal a highly porous silver network structure of the joint, with submicrometric silver grains and large micrometric porosities homogeneously distributed.

Zinc antimonide thin film based flexible thermoelectric module

Zinc-antimonide is an encouraging alternative thermoelectric material to bismuth telluride based material for medium temperature range applications. In this work two fabrication concepts are proposed to build flexible modules using P-type zinc-antimony thin film and constantan straps, where the constantan was used as flexible electrical interconnect and N-type thermoelectric element. Nano-silver paste was applied as the bonding material and adhesive substance to tolerate a higher range of temperatures. The thin film specimen consisted of a 600 nm thin layer of zinc-antimonide deposited by magnetron co-sputtering on a 350 µm thick glass substrate. The proposed device configurations generate peak power of 3.5 μW and 13.5 μW at hot side temperatures of 250 °C and 330 °C, respectively.

ITO and graphene-covered Ag grids embedded in PET substrate by thermal roll imprinting for flexible organic solar cells

The development of a low-resistive flexible transparent conductive film (TCF) was demonstrated by showing thermal roll imprinted and an embedded Ag grid. The Ag-embedded TCF shows excellent optical and electrical properties when the secondary layer of ITO and graphene is coated onto the flexible embedded Ag grid substrate. The TCF showed an extremely high transmittance of 77.56% with ITO and 77.73% with graphene; moreover, it showed a very low sheet resistance of 4.05 Ω/□ and 14.0 Ω/□ with ITO and graphene, respectively. This high performance is achieved by thermal imprinting of channels at 15 μm wide so that the DI-based nano silver paste filled in the narrow channels using Dr. Blade's method, thus providing the embedded pattern of Ag grid in the flexible PET substrate. The succeeding TCF performance was validated by fabrication of an OSC (organic solar cell) that exhibits excellent power conversion efficiency (PCE) of 2.649% and 2.551% for the ITO-Ag grid and graphene-Ag grid, respectively. This indicates that the hybrid flexible electrode using an intaglio method can be applied to transparent conducting electrodes for highly efficient opto-electronic devices.

Mechanical properties and microstructure of low temperature sintered joints using organic-free silver nanostructured film for die attachment of SiC power electronics

In this work, an organic-free silver nanostructured film (SNF) was applied to bond SiC chips and ceramic substrates, which was fabricated by ultrafast pulsed laser deposition (PLD). Unlike the commercial nano silver paste which contains 10%–30% organics, the bonding temperature of SNF could be reduced to only 180 °C, with the average shear strength of 18 MPa, ~3 times higher than the standard MIL-STD-883 K. The average shear strength of sintered joints reached 40 MPa when sintering temperature increased to 250 °C. The shear strength of joints was strongly dependent on their microstructure, especially the porosity and pore distribution of sintered layer. It can be tuned by size distribution and aggregation mode of particles in deposited SNF. Sintering mechanisms and strategies for obtaining appropriate mechanical property and porosity were discussed.

Corrosion effects on sintered nano-silver joints and the secondary biological hazards

Corrosion can affect the service life and reliability of electronic devices, in addition, corrosion products may flow out with sweat and enter the body through skin. In the current study, mechanical and biological corrosion experiments were performed to explore the mechanical properties and secondary biological hazards of nano-silver paste in the corrosive environment. The effects of corrosion time on shear strength and corrosion products of sintered nano-silver joints on biological organism were investigated. The survival rate of hamster lung cells was measured by MTT assay and flow cytometry after cultured in nutrient solution containing different concentration of nano-silver particles. Experimental analysis reveals that the shear strength of sintered nano-silver joint decreases drastically with the increasing of corrosion time, and the fracture mode changes from interlayer to interfacial fracture. A modified Weibull statistical model was proposed to predict the average failure strength and probability of sintered nano-silver joints at different corrosion time. In addition, biological experiment demonstrates that with increasing of nano-silver particles concentration, the survival rate of hamster lung cells firstly increases and then decreases.

A variable-order fractional model of tensile and shear behaviors for sintered nano-silver paste used in high power electronics

Next generation power electronics demand not only miniaturization and integration, but also higher power and harsher operation conditions. However, the conventional lead-free solders can't meet these requirements. Sintering of nano-silver paste has already become one of popular substitutes, as it can achieve low temperature packaging and high temperature operation. The mechanical performance of sintered nano-silver paste is of great importance for its applications in high power electronics. In this study, a variable-order fractional constitutive model is adopted to characterize tensile behaviors of sintered nano-silver paste at different strain rates and ambient temperatures. A comparative study with the well-known Anand model is conducted to present the advantages of the proposed model with simpler formulation, higher accuracy and fewer parameters. The fractional order is also found to well indicate the evolution of mechanical properties along with varying strain rates or temperatures. Furthermore, the model is firstly extended to describe shear experimental data at different temperatures, especially those with strain softening stages. All simulation results reveal that the variable-order fractional model is an effective tool in characterizing both tensile and shear behaviors and demonstrating the evolution of mechanical properties.

Low-temperature copper bonding strategy via hierarchical microscale taper array fabricated by femtosecond laser

In this study, a facial and effective method is proposed to improve interfacial bonding strength via a hierarchical microscale taper array fabricated by a femtosecond laser. Copper interfaces with microstructures can be easily sintered by nano-silver paste under low bonding temperature and additional pressure. In order to analyze the sintering quality, the interconnected cross-section is characterized after a shear test. The shear strength of copper with microscale taper arrays under different sintering pressures is also investigated. Experimental results show that the shear strength of the interconnected Cu interface with a microscale taper array is greatly improved, reaching up to 65.53 MPa at a low bonding temperature of 260 °C. It is demonstrated that the enhancement of shear strength is mainly due to the increase of contact area and mechanical locking. This technology could provide more possibilities for electronic packaging interconnection under low-temperature and low-pressure conditions.

Improvement of Sintering Performance of Nanosilver Paste by Tin Doping

Nanosilver paste, an interconnect solder, is a common choice in the electronics packaging industry. However, higher sintering temperature and lower sintering strength limit its application. At present, doped nanosilver paste has been studied for use in chip interconnection. In order to improve the sintering properties and shear strength of nanosilver paste, we have developed a new tin-doped nanosilver paste (referred to as silver tin paste), and according to the decomposition temperature of the organic dispersant in the slurry, a corresponding sintering process with a maximum temperature of 300°C was developed. The product after sintering of the silver tin paste is a mixture of a solid solution of Ag and an Ag3Sn phase. Among them, the hard and brittle phase Ag3Sn diffuse distribution in the silver matrix for strengthening, and the solid solution of Ag acts as a replacement solid solution strengthening. As the content of doped Sn increases, the sintering strength increases remarkably. When the Sn content is 5%, the joint shear strength reaches the highest value of 50 MPa. When it exceeds 5%, the sintering strength gradually decreases, which may be caused by the excessive formation of the intermetallic compound IMC as the dopant content increases. This new tin-doped nanosilver technology has the characteristics of low-temperature sintering and high-temperature service, so it is expected to be widely used in semiconductor power devices.

Feasibility investigation and characterization of low-pressure-assisted sintered-silver bonded large-area DBA plates

PurposeThis paper aims to use nano-silver paste to design a new bonding method for super-large-area direct-bonded-aluminum (DBA) plates. It compared several frequently used bonding methods and proved the feasibility of an optimized low-pressure-assisted double-layer-printed silver sintering technology for large-area bonding to increase the thermal conductivity of power electronic modules with high junction temperature, higher power density and higher reliability.Design/methodology/approachThe bonding profile was optimized by using transparent glasses as substrates. Thus, the bonding qualities could be directly characterized by optical observation. After sintering, the bonded DBA samples were characterized by nondestructive X-ray computed tomography system, scanning electron microscopy equipped with an energy dispersive spectrometer. Finally, bonding stress evolution was characterized by shear tests.FindingsLow-pressure-assisted large-area double-layer-printed bonding process consisting of six-step was successfully developed to bond DBA substrates with the size of 50.8 × 25.4 mm. The thickness of the sintered-silver bond-line was between 33 and 74 µm with the average porosity of 12.5 per cent. The distribution of shear strength along the length of DBA/DBA bonded sample was from 9.7 to 18.8 MPa, with average shear strength of 15.5 MPa. The typical fracture primarily propagated in the sintered-silver layer and partially along the Ni layer.Research limitations/implicationsThe bonding stress needs to be further improved. Meanwhile, the thermal and electrical properties are encouraged to test further.Practical implicationsIf nano-silver paste can be used as thermal interfacial material for super-large-area bonding, the thermal performance will be improved.Social implicationsThe paper accelerated the use of nano-silver paste for super-large-area DBA bonding.Originality/valueThe proposed bonding method greatly decreased the bonding pressure.

Preparation of Nano Silver Paste and Applications in Transparent Electrodes via Electric-Field Driven Micro-Scale 3D Printing.

Nano-silver paste, as an important basic material for manufacturing thick film components, ultra-fine circuits, and transparent conductive films, has been widely used in various fields of electronics. Here, aiming at the shortcomings of the existing nano-silver paste in printing technology and the problem that the existing printing technology cannot achieve the printing of high viscosity, high solid content nano-silver paste, a nano-silver paste suitable for electric-field-driven (EFD) micro-scale 3D printing is developed. The result shows that there is no oxidation and settlement agglomeration of nano-silver paste with a storage time of over six months, which indicates that it has good dispersibility. We focus on the printing process parameters, sintering process, and electrical conductivity of nano-silver paste. The properties of the nano-silver paste were analyzed and the feasibility and practicability of the prepared nano-silver paste in EFD micro-scale 3D printing technology were verified. The experiment results indicate that the printed silver mesh which can act as transparent electrodes shows high conductivity (1.48 Ω/sq) and excellent transmittance (82.88%). The practical viability of the prepared nano-silver paste is successfully demonstrated with a deicing test. Additionally, the experimental results show that the prepared silver mesh has excellent heating properties, which can be used as transparent heaters.

Dynamic Resistance Monitoring of Nano Silver Paste during Sintering and Thermoelectric Aging Process

Dynamic Resistance Monitoring of Nano Silver Paste during Sintering and Thermoelectric Aging Process